Contents...spallation and dissolution in the glass melt, resmct their use. The best combination of properties for use in the molten glass environment are provided by the platinum group

UK ISSN 0032-1400

PLATINUM METALS REVIEW

A quarterly survey of research on the plat inum metals and of developments in their application i n industry

VOL. 37 APRIL 1993

Contents

Advanced Coating Technology A.C.T.TM

Availability of Platinum, Palladium and Rhodium

Ultra Micro Glutamate Sensor

Rhodium and Palladium Compounds

Supported Palladium Catalysts

Aluminium-Ruthenium High-Temperature Alloys

Knitted Platinum Alloy Gauzes

Some Diverse Aspects of the Platinum Metals

The Modification of Superconductors

A Selective Review of Metal-Hydrogen Technology in the Former U.S.S.R.

Reduction of Nitrogen Oxides by Hydrocarbons

Nanoscale Platinum Technology

Early Studies of Platinum in Spain

Abstracts

New Patents

NO. 2

62

70

70

71

72

75

76

85

86

97

101

101

102

108

119

Communications should be addressed to The Editor, Platinum Metals Review

Johnson Matthqr Public Limited Company, Hatton Garden, London ECl N 8EE

Advanced Coating Technology A.C.T.TM MORE EFFECTIVE USE OF THE PLATINUM METALS WILL BENEFIT THE GLASS MANUFACTURING INDUSTRY

By D. R. Coupland Johnson Matthey Technology Centre

The glass industry manufactures a multitude of products ranging fiom domestic glass table- ware to “high tech” optical glass. In its most basic form, such glass is a combination of soda lime and silica with additions of modifiers and refin- ers, and when molten it is a very aggressive substance. During product manufacture much of the process equipment is subjected to severe environments, which may involve high temperatures, or corrosive chemicals, or both, and equipment will be in contact with both liquid glass and the glass vapour. In view of this, difficulties are encountered in the containment, handling and processing of glass. A need therefore exists for materials which have excellent corrosion resistance and good stability at high temperatures; such properties are typical of the platinum group metals.

At first sight, transition metals, such as nickel and iron, and the refkactory metals molybdenum and tungsten, with their excellent mechanical properties and modest cost, make ideal candidates for use in the glass industry. The rehctory metals, notably molybdenum, are very useful in the molten glass environment, but only under strictly controlled conditions. The poor resistance to oxidation of transition metals and their alloys, however, results in apparatus having only a limited service life, leading to premature failure and colouring of the glass, see Figure 1.

By comparison, the rehctory oxides (ceramics) have high temperature stability but they suf- fer fiom relatively poor mechanical properties, notably brittleness and poor thermal shock resistance, and moderate resistance to corrosion by molten glass. The intrinsic disadvantages of lim-

A.C.TTM is a trade mark of Johnson Matthey PLC.

ited thermal shock resistance, combined with spallation and dissolution in the glass melt, resmct their use.

The best combination of properties for use in the molten glass environment are provided by the platinum group metals and their alloys, which are characterised by high melting points and excellent chemical nobility. Platinum is one of the most inert of the group, and it is relatively non-reactive with most glass melts up to approximately 1450°C; however, the service life of conventional platinum alloys may be limited at higher temperatures by grain growth. Over many years, a range of zirconia grain stabilised (ZGS) alloys, which contain very fine, uniform dispersions of oxide particulates, has been developed by Johnson Matthey (1). Such dispersions restrict mimstructural degradation and &ectively mend the operating life at these higher temperatures. The manufacturing process for ZGS alloys pro- motes the formation of a high aspect ratio grain structure. This elongated structure is extremely stable even at very high temperatures and results in alloys which exhibit the highest tensile strengths, creep properties and general durability levels of all comparable platinum group metals and alloys, see Figure 2; thus they are emi- nently suitable for use in the glass industry (2).

The use of ZGS platinum group metals and alloys has enabled cost effective solutions to be achieved for a wide range of industrial problems. There are, however, a number of other applications for which the platinum group metals would provide the ideal technical solution, but where, because of their intrinsic value, the advantage gained would be insufficient to just@ their use in bulk.

In some instances, alloying platinum group metals with base metals can be used to obtain

Platinum Metals Rev., 1993,37, (2), 62-70 62

Fig. 1 Two examples of nickel- chromium alloys shown after partial immersion glass testing at 1200°C for 100 hours. The use of unprotected nickel can result in the early failure of equipment and discoloration of the glass being p r d (a) shm eorroBive attack at the air/sulmtrate/glaaa interfa- and (b) shows build-up of oxide resulting from gross oxidation of the nickel alloy in the glass vapour

improved mechanical properties and decreased costs, but there is a related reduction in resistance to the harsh conditions encountered in service.

For components of relatively simple shape one solution has proved to be the use of platinum group metal claddings on ceramic or base metal

substrates in place of bulk platinum group metals. This has resulted in reduced cost components with appropriate properties.

Now, new Advanced Coating Technology (A.C.T.TM) (3), which is being introduced by Johnson Matthey, will allow the advantageous properties of platinum group metal claddings,

Fig. 2 The stre%e rupture properties of platinum ZGS alloys are shown at 140O0C. The microstructures of ZCS platinum group metals and alloys are stable at high temperatures

i d propertiea make them emi- nently suitable for use in the glass industry

and th& mechanical end &em-

I 10 too moo

TIME TO RUPTURE, hours

Plarinum Metals Rev,, 1993,31, (2) 63

currently available for only a small mnge of products, to be used in both traditional and new areas of application, especially on more complex shapes. This A.C.T.TM platinum group metals coating technology will extend the existing fused salt and aqueous Q-salt plating (4) capability of Johnson Matthey,

Coating Technology The prime objective of a coating is to achieve

a combination of the best properties of the substrate and the coating, while diminishing their less favourable characteristics. In the case of platinum coatings, the aim is to retain the mechanical properties of the substrate and confer on it the beneficial environmental resistance provided by platinum. By coating with platinum, the poor corrosion resistance of the substrate is improved, while the high density and the cost are lowered relative to those of bulk platinum. Mechanically cladding a substrate with platinum goes part way towards this ideal, but the lack of an integral bond between the substrate and the cladding means that the two materials act independent- ly. However, the intimate nature of A.C.T.TM coatings enables them to develop synergistic characteristics with the substrate.

At high temperatures the use of coatings or claddings is potentially limited by their interaction with the substrate. This interaction is predominantly controlled by dif€usion and can lead to rapid degradation of the coating, with significant loss ofproperties (5). The whole A.C.T.TM process has been modelled by computer using available diffusion data (6) and standard equations. This enables predictions to be made of the likely behaviour of various combinations of materials, over chosen temperature ranges and times, although these can only serve as a general guide to the actual performance of the materials under service conditions.

One example of a computer modelled prediction of how nickel and chromium could be expected to diffuse through a platinum coating is shown in Figure 3. The prediction indicates that after only 24 hours at 120OOC there would be extensive diffusion of both base elements into a 10 pn platinum layer. Actual nickel-chromium

A k y substrate

THICKNESS, PIT

Fig. 3 Schematic of nickel and chromium diffusion through a platinum coating, ae predicted by computer modelling for a temperature of 1200OC and a time of 5 hours

substrates, plated with 15 and 25 pm of platinum, are shown in Figure 4 after partial immersion for 24 hours in molten glass at 1200°C. The platinum coatings have been degraded by the outward diffusion of nickel (indicated by the green coloration) and also by the effects of thermal stress, leading to total disruption in the case of the thinner coating. Thus experimental behaviour was comparable with the predictions of the model, which was subsequently used to develop more complex coating systems able to overcome the problem of diffusion. Following extensive laboratory experiments and trials of systems selected on the basis of predictions h m the mod- els, a complex coating system designed to overcome the effects both of diffusion and differential thermal expansion between substrate and coating has been developed.

The make-up of the coating system is depen- dant upon the substrate to be protected and the intended service environment. For example, to protect nickel-chromium type substrates the coating consists of several distinct layers, each of which has one or more functions:

(i) To o s e t any mismatch between substrate and protective outer layer, which results from variations in thermal expansion characteristics. The strains ar is ing fiom such differences can be large and must be accommodated by the ductil- ities of the interlayers together with their thermal expansivities.

(ii) To slow interdiffusion between the

Platinum Metah Rev., 1993, 31, (2) 64

Fig. 4 The effects of 24 hours partial immersion in molten glass, at 12OO0C, on a nickel alloy coated directly with platinum; (a) shows glass line disruption of a 15 pm platinum canting and (a) shows *ion

a 25 pm coating of platinum ofnickeldchromiumthmugh

constituents of the outer protective coating and or a platinum group metal, although this could the underlying substrate material. Such inter- be varied significantly depending on the W s i o n is usually deleterious. specific service requirements.

(iii) To key the other layers together in order to improve mechanical integrity. Testing the Coatings

The total coating thickness may be as low as The A.C.T?' coating system was designed to 250 pm, but it can be substantially greater. Of enhance the surface properties of substrates with this thickness, 150 to 200 pn is usually platinum inherently good mechanical properties andor

Fig 5 The working end of a platinum A.C.T.I" coated tri- level thermocouple assembly after 2800 hours of forehearth service at 1200OC

Platinum Metals Rev., 1993,31, (2) 65

thermal stabilities at high temperatures. Considerable laboratory testing of such coatings was undertaken before the work was extended to include field trials of protected nickel-chromium alloys. This work was performed in forehearths of major glass container companies in the U.K. and in Australia. With typical molten glass temperatures of between 1 100 and 12OO0C, substrate protection was achieved for up to the maximum test time of 4500 hours, Figure 5.

It was recognised that this technology was limited by the strength of the substrate material at high temperatures, which in the case of nickel- chromium alloys imposed an upper temperature limit of 1200 to 1250°C. This temperature maximum would limit the applications of the coated materials to only a hction of their potential uses in the glass industry. Attention was therefore transferred to the development of protection for higher temperature substrates, namely the rehctory ceramics.

A.C.T.m Coatings on Ceramics The technology developed to provide protec-

tive coatings for nickel based alloys was extended further to allow its application to some of the many varieties of refractory ceramic substrates (7). Mullite tubes, closed at one end, were used as substrates in the first mals, which were performed at temperatures up to 135OOC. During this phase of laboratory testing the thickness of

the platinum in the protective coating system was between 150 and 400 p. Failure of the alumina crucibles used to contain the molten glass limited the duration of tests to about 500 hours at 1200”C, and to 100 hours at 1350°C.

Components coated using the A.C.TJM system were subjected to extensive investigation and analysis in tested and untested conditions. Only after this were field tests undertaken using A.C.T? on tri-level thermocouple assemblies, see Figure 6. The early field tests were undertaken in a forehearth operated by a glass container manufacturer, and the first components were subjected to temperatures ofup to 1200°C in molten flint, amber and green glasses, in suc- cession. Sufficient confidence was gained in the performance of these coated tri-level thermocouples to allow their use as part of an integrated system for glass temperature control. Now in its eleventh month of use, the A.C.T.TM coated assembly is still “problem free”.

An example of a mullite substrate protected by a 10 per cent rhodium-platinum A.C.Tm system is shown in Figure 7.

Following the first field tests, further components have been tested in forehearths at various glass plants located around the world. These trials have involved mullite substrates, and various thicknesses and compositions of platinum group metal A.C.T.TM coatings have been used to pmvide the protection over Werent lengths of the

Fig. 6 A sehematic repreaenta- tion of a tri-level thermoeouple assembly showing the furnace roof, gaa space, glass and furnace floor. The exploaea view shows the g l d a i r thermocouple interface

Platinum Metals Rent., 1993,37, (2) 66

Fq. 7 The working end of a tri- level thermocouple assembly with part of the mullite tube A.C.T.m coated with 10 per cent rhodium-platinum, shown after lo00 hours of forehearth service

component. All have performed extremely well, and have even shown some unexpected additional benefits. For example, one user has observed significant reductions in the “noise” associated with thermocouple readings, compared with that from conventional products having the same protected length.

Although much of the research and development work used mullite as a substrate, other rehctories have also been successfully protected by A.C.TTM systems. These have ranged firom high purity alumina to almost pure silica, including materials such as zircon-mullite and alumina-silicates. Work to extend the variety of substrates which can be protected by A.C.T.TM systems is now being undertaken.

Within the glass industry this technology could be applied to the protection of a wide variety of components including the rotors for fibre glass production, bubbler tubes, electrodes, skimmer blocks, flow control devices, gobbing units, stir- rers, orifice rings and other special delivery-forming equipment and furnace furniture. Commercialisation has now begun, primarily for thermocouple sheathing.

The Tri-Level Thermocouple Aeeembly Design

The protection of thermocouples is the starting point for the commercial application of A.C.TTM technology. This is particularly directed at the arduous service environments associated

with the intrusive monitoring of glass temperatures either in forehearths or in melting furnaces (8 ,9) . One important sub-group of thermocouples is the m-level thermocouple.

In this particular application the benefits resulting from the use of A.C.T? on thermocouple assemblies in preference to conventional cladding include the ability to cwtomise a standardised basic assembly design with:

variable assembly length variable coating length variable coating thickness profiles variable composition of the coating material.

Thus the specific requirements of a customer can be rapidly fulfilled.

The Financial Benefits of Using A.C.T.m In addition to the technical benefits resulting

h m the integration of the substrate and the protective metal coating, the A.C.T? system also confers the potential for significant financial benefits to accrue from the more effective use of the platinum group metals. First, protective A.C.Tm coatings can be prepared at thicknesses down to 175 p, which compares favourably with the lower limits for conventional cladding procedures, which are about 350 to 400 p. Secondly, platinum group metal layers of 400 p thick, or more, can easily be achieved by A.C.T?‘ over critical areas of components where enhanced durability or other specific properties a~ required for a particular application. Importantly, AC.TTM

Platinum Metah Rev., 1993,31, (2) 67

Comparison of mid Thicknese Profilea for an A.C.T.m Coated and a Conventionally Clad Tri-Level Thermocouple Sheath

I

Length of segment for coating, cm

A 15 B 5 c 10

Thickness, p n

A.C.T.TM

E 175 G 350 F 200 d Substrate diameter 1.4 cm

Clad

350 350 350

1.4cm

i I

technology enables the thickness of the platinum group metal coating, and thus the protection provided, to be matched to the various service conditions encountered at Merent parts of the same component.

Qpical dimensions of A.C.T? and conventional coatings used on a traditional design of tri-level thermocouple sheath are shown in the Table, while the cost benelits, see Figure 8, which may result from the more effective use of the platinum group metals can be deduced h m the Table by a comparison of the relative weights of the metals used.

Gathering Balls The transfer of molten glass into moulds can

be accomplished by a number of techniques, with the selection being based on the volume and speed of the required transfers. At low rates a gathering or transfer ball is used (10); this utilis- es the rotation of the ball and the viscosity of the melt to achieve “carry over” of the glass. Traditionally iron balls were used - a natural extension of the blowing iron, but more recently ceramic balls were introduced, mainly to elim- inate problems resulting h m contamination of the glass with iron. These balls are available in a

Platinum Me& Rev., 1993,37, (2)

wide range of sizes and compositions but all have some basic disadvantages, such as being sus- ceptible to corrosion, the severity of which depends on the composition of both the ball and the glass. This corrosion may result in the production of blisters and perhaps even stones in the glass. The gathering balls also tend to be sus- ceptible to sudden failure due to thermal shock or thermal cycling, so they must be carefdly pre- heated before use and maintained hot between campaigns. The operatingregimes required, even when successful, cause considerable loss of production time.

Recent trials of gathering balls made of selected ceramic substrates clad with A.C.T?‘ platinum coatings, see Figure 9, have shown that considerable progress has been made in overcoming the problems discussed above. In addition to overcoming corrosion, gathering balls with coatings of 200 pm nominal thickness have demonstrated excellent glass transfer characteristics, have enabled start-up times to be min- imised and have shown tolerance to repeated stopstart cycles.

To date trials have been performed in borosil- icate glasses and in lead crystal, with operating temperatures in the range 1200 to 1400OC. To enable the gathering balls to be examined, trials have now been curtailed after several weeks of operation. An evaluation of the potential for using A.C.T? on transfer balls is sti l l being carried

Fq. 8 A comparison of reletive mhiosic UH~S of platinum group metals used in conventional claddings #Z and Johnson Matthey A.C.T.m coatings clearly demonstrates the benefits of th is technology

68

Fig. 9 A platinum A.C.T."' coated ceramic gathering ball streaming molten glass, during service trials

out, and the potential benefits of using platinum p u p metal alloys as alternatives to platinum are also being examined and assessed.

Other Components One of the exciting aspects of the A.C.T.TM

coating technology is its versatility. It can be applied to a wide range of component shapes. Indeed the major benefits of the technology to users are expected to occur &om the elimination or reduction of component failure, which otherwise d t s in major production downtime. Many of these components are complex in shape and

therefore not amenable to cladding by the traditional techniques. On such shapes A.C.T.TM will allow the utilisation of platinum group metals, and their use wil l be readily justified by the ensuing extension of component operating life andor improvement in product quality.

A large component coated with 10 per cent rhodium-platinum alloy by A.C.TTM has been supplied to a major European glass manufacturer.

Summary and Conclusions Despite their inherent disadvantages, notably

brittleness, poor thermal shock resistance and poor resistance to molten glass corrosion, the rehctory ceramics have for many years been the preferred materials of choice for equipment used in the glass industry. In many of their applications satisfactory performance is achieved by regular replacement. In other situations, platinum and its alloys, which are also accepted as essen- tial materials for the fabrication of crucial components, are used to clad the rehctory ceramics with a protective coating. The use of cladding is, however, limited by the complexity of the shape of the subsmte which can be satisfactori- ly clad, and by the minimum thickness which can realistically be applied.

These restrictions can be overcome by A.C.T.TM, so there will be opportunities for A.C.T.TM platinum group metal coatings on ceramics to progress into areas of glass production technology where the cost of bulk platinum group metals has inhibited their use, or where the process of cladding is too unwieldy, or indeed technically non-feasible.

Platinum group metal A.C.T.TM coatings have several advantages over cladding:

Easier and more effective protection of diB- cult-to-clad intricate shapes

Thinner platinum group metal layers, leading to lower metal costs

Thickness profiling of platinum group metals Elimination of cementing or mechanical fixing

of protective layer to substrate Elimination of welding platinum group metals Use of alloys which are not amenable to

cladding. As in any industry, the glass manufacturers

Platinum Met& R a . , 1993,31, (2) 69

are not only looking to improve the quality of their product but also to achieve economies in production.

To these ends, the benefits which users of A.C.T.TM coatings should derive will include

improved reliability of the coated component, i m p d thermal shock mistance, reduced down times, and generally maintained or improved quality of the glass end product, with respect to both defects and to dimensional tolerances.

References 1 R B. McGrath and G. C. Badcock, Mmimm2 Metals

Rea, 1987,31, (l), 8; and the reference therein 2 J. Stokes, Platinum M e 4 Rev., 1987,31, (2),54

4 P. E. Skinner, Platinum Metals Rev., 1989,33, (3),

5 D. Ott and Ch. J. hub, PIaninUn M&als Rev., 198

6 “Metals Reference Book”, Smithells, 5th Edn.,

7 pending European Appl., 931300,823

9 D. A. Toenshoff, G h s , 1992,69, (l), 21

Butterworths, 1976, London

Johnson Matthey pLc> AHz. 471,505A 8 R.W. M Marshall, Glass, 1989,&, (6)

102

31, W,64 10 W. Lindner Maschinen, Glassmachinery Pkznts &

Accessories, 1992, V, (4), 43

Availability of Platinum, Palladium and Rhodium In view of their widespread use in the auto-

motive, chemical, electronic and petroleum industries the platinum metals are regarded as strategic materials in the United States of America. For this reason the US. Bureau of Mines collects and evaluates information relating to their availability and demand. A previous report from this organisation was published in 1982, based on data - from the so-called market economy countries - available up to 1980 (1). Since then major changes have occurred in the supply of these metals as the industry prepared to satisfy the increased demand expected to result from new anti-pol- lution legislation, particularly in countries of the European Community.

This earlier study has now been updated following a complete re-evaluation of resources, industry structure and costs (2). Based on 1989 data, the new report commences with an overview of supply and industrial demand for platinum, palladium and rhodium. A further section considers the resources, cost and economic factors that affect the availability of the platinum metals, and includes pricing and price proportion analysis, and availability analyses. Data are presented in a total of thirty-four figures and tables, and this main part of the report is supported by 106 references.

In an appendix, demand and uses for the platinum metals are summarised. Environmental uses are regarded as some of the most critical of the many industrial applications; demand for jewellery and investment are also considered. In other appendices the methodology employed in this study is explained, the major mining properties in Southern Africa and North America are described, and mining, treatment

and autocatalyst recycling processes are summarised briefly.

This most informative fifty-four page report is available without charge from: Chief, Branch of Minerals Availability; U.S. Bureau of Mines; 810 7th Street, Nw, Washington, DC 20241- 5202; U.S.A. For technical information, contact Catharine T. Fogg or Joseph L. Cornellisson at the Minerals Availability Field Office; U.S. Bureau of Mines; Building 53, Denver Federal Center; Denver, CO 80225; U.S.A.

References 1 T. F. Anstett, D. I. Bleiwas and C. Sheng-Fogg,

“Platinum Availability-Market Economy Countries”, IC 8897, U.S. Bureau of Mines, Washington, 1982,16pp

2 C. T. Fogg and J. L. Cornellisson, “Availability of Platinum and Platinum-Group Metals”, IC 9338, US. Bureau of Mines, Washington, 1993, 54PP

Ultra Micro Glutamate Sensor Microbiosensors based on semiconductor

fabrication technology are of the order of mil- limetres in size, but significantly smaller electrodes are required for insertion into the brain or nerve tissue. Now researchers in Japan have constructed an integrated ultra micro enzyme sensor with a 7 pm diameter platinised carbon fibre disc electrode and a platinum thin film counter electrode (E. Tamiya, Y. Sugiura, T. Takeuchi, M. Suzuki, I. Karube and A. Akiyama, Sens. Actuators B, 1993, 10, (3),

The surface of the carbon fibre electrode was platinised electrochemically, which increased the electrode activity sufficient for the sensor to be used for the determination of glutamate, an important neurotransmitter.

179-184).

Platinum Memk Rev., 1993, 31, (2) 70

1 R B. McGrath and G. C. Badcock, Mmimm2 M& Rea, 1987,31, (l), 8; and the reference therein

2 J. Stokes, PlatinumMetrJcRev., 1987,31, (2), 54 3 Johnson Matthey PLC, European Appl. 471,505A 4 P. E. Skinner, Platinum Metals Rew., 1989,33, (3),

5 D. Ott and Ch. J. hub, FIaninun M& Reu, 1987, 102

31, W,64

Rhodium and Palladium Compounds - Transition Metal Organometallica for Organic Synthesis BY F. J. MCQUILUN, D. G. PARKER AND G. R. STEPHENSON, Cambridge University Press, Cambridge, 1992,594 pages, ISBN 0-521-33353-9, LlOO, U.S. $200.00

Interest in the application of transition metal organometallics towards organic synthesis has been growing steadily over the past twenty-five years, and this book is directed at newcomers to the field. It highlights the major synthetic methods which employ organometallic reactions and covers the literature up to the end of 1988.

The h t chapter provides an introduction with an emphasis on the reactivity of ligands co-ordinated to metals. The next eleven chapters deal with application by reaction or complex type, and form the bulk of the text.

A chapter on isomerisation includes the application of rhodium to carbon-carbon double bond isomerisation, which is used industrially in 1- menthol synthesis. The relevance of palladium and rhodium in other rearrangements, such as the ring opening of cyclopropanes and epoxide rearrangements, is also discussed.

The oxidation of alkenes is dominated by the palladium catalysed Wacker process, and this, the extension of the chemistry to natural product synthesis and the introduction of masked ketones into molecules, is examined in Chapter 4. This is followed by a section on co-ordinated alkenes and alkynes as synthetic intermediates where the addition of nucleophiles to alkenes may be facil- itated by palladium reagents or catalysts. The next chapter describes palladium x-ally1 complexes. After dealing with their stoichiomemc formation and alkylation, their catalytic applications, including reaction stereochemistry, asymmetric synthesis and types of nucleophile for use in allylic alkylation, are discussed.

Carbonyl insertion is discussed in Chapter 9. The indusmal importance of the hydroformylation reaction is illustrated by cobalt and rhodium catalysts and the development of the low pressure rhodium 0x0 process to produce butanal. The application of this chemistry to form: per- fumery chemicals, such as homocitronellol, ketones, lactones and asymmetric carbonyls with

related rhodium catalysts is described. Carbonylation using palladium reagents is exemplified by the synthesis OfpSUbstituted carboxylic acid derivatives, dicarboxylates and the application of intramolecular variants of carbonylations to the synthesis of lactones. However, the preferred industrial route to acetic acid, by rhodium catalysed carbonylation of alcohols, occupies only as much space as discussion of the rhodium catalysed reaction of carbon monoxide with hydrogen to form ethylene glycol, which received much attention in the early 1980s.

Further insertion and coupling reactions are examined in Chapter 10. The use of complexes of rhodium and ruthenium, containing phosphine ligands for hydrogenation reactions, especially carbon-carbon multiple bonds, is described as are platinum and rhodium complexes for hydrosilation. Palladium reagents and catalysts are useful for a myriad of coupling reactions involving unsaturated hydrocarbon fragments.

Chapters on organomedic cycloaddition reactions and carbene complexes provide more examples of the versatile palladium and rhodium reagents, such as palladium compounds to effect annulation reactions, and rhodium carboxylates to close the J-lactam ring in the synthesis of methylcarbapenums.

The fmal three chapters cover special topics, and subjects dealt with elsewhere in the-book are pulled together. The synthetic strategies to be achieved using the unusual reactivity profiles of organotransition metals are emphasised. These different strategies are exemplified by the Wilkinson rhodium catalyst in achieving depro- tection via isomerisation of alkenes, in natural product syntheses where palladium reagents can aid the synthesis of pheromones via oxidation.

Cross-referencing deals adequately with topics covered in more than one chapter, and the book is illustrated by clear diagrams with over 1700 references. M.J.H.R

Platinum Met& Rev., 1993, 37, (2), 71 71

Supported Palladium Catalysts A COMPARISON OF SOLVATED METAL ATOM IMPREGNATED AND CONVENTIONALLY PREPARED CATALYSTS

By X.-Z. Jiang’

S.-J. Yang and S.-H. Wu

Department of Chemistry, University of Zhejiang, Hangzhou, P.R. China

Department of Chemistry, University of Nakai, Tiangin, P.R. China

In the last fifteen years a promising new method for preparing highly dispersed supported metal catalysts, called solvated metal atom dispersion (SMAD), has been developed by Klabunde and co-workers (1-9). This method employs the metal vapour technique, where metal atoms, such as nickel, cobalt, iron and magnesium, are solvated at liquid nitrogen temperature, 77 K, in toluene or some other appropriate solvent. Upon being warmed, the solvate decom- poses and metal clustering begins. The nucle- ation process competes with a “reaction channel’’ where the growing clusters react with the host solvent. These growing clusters incorporate

carbonaceous fragments, resulhg from the cleav- age of organic solvent, and are stabilised as arnor- phous “pseudo-organometallic” powders. The powders represent a special new class of materials which behave as novel heterogeneous catalysts. The incorporated carbonaceous fragments do not poison the catalysts, but instead aid their catalytic activity (1 0) and apparently provide a better means of attaching the metallic particles to the catalyst support surfaces (5,7, 11).

In the present work, which is based on the SMAD method, a modified technique, called SMAI - solvated metal atom impregnation - and described in the Scheme, has been used

correspondence to Hangzhou Semiconductor Company, Hangzhou, Zheijiang, P R. China

SMAI Method

4hoys -A*C 1 su-

Sequences for the preparation of supported palladium eatalyste by sobated metal atom impregnation (SMAI) and by conventional impregnation ( C I ) methods

Platinum Metals Rev., 1993, 31, (2), 72-75 72

Table I

Elementary Analysis of the Carbon and Hydrogen Content in the Samples I

Sample Carbon, per cent

0.42% Pd/SiO, (SMAI) 0.42% Pd/Si02 (CI) 1.39% Pd/AIzOs (SMAI) 1.39% Pd/AIzO3 (CI) 1 SO% PdRrOz (SMAI) 1 SO% PdRrOz (CI) 1.56% Pd/MgO (SMAI) 1.56% Pd/MgO (CI) 1.65% Pd/liOz (SMAI) 1.65% PdlliOz (CI)

Hydrogen, per cent

0.9 No 2.0 No 1.5 No 1 .o No 1.2 No

0.8 No 1.5 No 0.9 No 0.6 No 1 .o No

for preparing various supported palladium catalysts. The reactions chosen for study are the methanation of carbon dioxide in a flow system under a pressure of 10 atmospheres and the hydrogenation of benzene in an autoclave, the latter yielding mainly hexamethylene. For comparison corresponding supported palladium catalysts prepared by conventional impregnation, CI, are also shown in the Scheme.

Results and Discussion Catalysts were prepared by the solvated metal

atom impregnation method using purified toluene as the solvating medium. The purified supports, of silica, y-alumina, magnesia, zirconia and titania were introduced into the system by a spe- cially designed Schlenk Operating Line. The occurrence of carbonaceous fragments in the supported palladium SMAI catalysts was confirmed by elementary analysis and by the pyrolysis of a catalyst under a stream of hydrogen. The carbon and hydrogen contents in the SMAI samples are given in Table I. It can be seen that the SMAI catalysts contain a small amount of organic fragments which were formed during the preparation, and result from the decomposition of toluene. Furthermore, Figure 1 shows methane release upon pyrolysis of a 1.39 per cent palladium supported on alumina (SMAI) catalyst under hydrogen, as a function of temperature. This indicates that the supported palladium SMAI catalyst is rich in carbonaceous species

which are mainly in the form of C, species, such as C, CH, CH,, etc. These C, species contribute to the formation of methane only under a hydrogen stream. Thus at this stage the small palladium crystallites in the SMAI samples are sur- rounded by a layer of residual carbonaceous species, and then the tiny crystallites combine to form clusters of metal particles which then attach to the support surface through carbonaceous link- ages. Therefore as a catalytic centre, the small palladium cluster is pseudo-organometallic in nam, as well as being present in a -dispersed form.

The average size of palladium particles in SMAI catalysts is less than 2.0 nm, which is about ten times smaller than those in the corresponding CI catalysts, see Table II. Such high dispersions of metallic particles (clusters) in SMAI

950 200 2w a TEMPERATUR 350 400

'C

Fig. 1 The rate of methane released upon pyrolysis on a 1.39 per cent palladium supported on alumina catalyst under hydrogen

Plazinum Meralc Rev., 1993,31, ( 2 ) 73

Table II

Comparison of Palladium Particle S i z e s and Extent of Reduction for Supported SMAI and CI Catalysts

TEM

1.4

1.6

1.7 6.8

15

11

Catalyst reduction, per cent Oxygen titration

95 58 98 45 95 52

I Particle size. d. nm I Extent of

0.42% PdSiO, (SMAI) No 0.42% PdSiO, (CI) 1.50% Pd/ZrOz (SMAI) No 1.56% PdlMgO (SMAI) No

1 1.65% PdlTiOz (SMAI) No ~ 1.65% Pd/liOz (CI)

H,, 400°C, 3 h

1.56% PdlMgO (CI) H,, 400"C, 3 h

H,, 4OO"C, 3 h

Hydrogen adsorption

0.42 % Pd/SiO, (SMAI) 0.42 % Pd/SiO, (CI) 1.39 % Pd/Al,03 (SMAI)

1.56 % PdlMgO (SMAI) 1.56 % PdlMgO (CI)

1.39 % Pd/AIzOa (CI)

1.8

1.6

1.8 6.9

19

14

samples are attributed to their extremely mild preparation conditions, whereas the metallic particles on CI samples are formed under high temperature hydrogen treatment conditions and only achieve a low dispersion. In addition to the dispersions, Table II also shows another important feature, which is the extent of the reduction of the supported metal in the SMAI samples. The percentage reduction of palladium particles on these SMAI catalysts, measured by oxygen titration, reaches 95 per cent, which is almost twice that of the corresponding CI catalysts.

Since the supported palladium SMAI catalysts possess such novel characteristics they behave differently, for example during carbon dioxide methanation and benzene hydrogena-

tion, in their catalytic activity and selectivity. Comparisons of these catalytic behaviours are illustrated in Tables 111 and IVY respectively. From Table III it can be seen that the rates of methane formation on the SMAI catalysts are much higher than those on CI catalysts, especially for palladium supported on titania. The existence of a support effect on the reactivity for methane formation is ,observed, with the order titania > zirconia > magnesia > silica. For benzene hydrogenation, however, no obvious support effect is observed and the supported palladium SMAI catalysts exhibit unusual reactivity and selectivity compared with the corresponding CI catalysts.

In short, comparing the catalytic behaviours

Tabk 111

Cornpariaon of Catalytic Activity of Supported Palladium Catalysts Prepared by SMAI and CI for Carbon Dioxide Methanation'

Catalyst Treatment Rate of methane formation, mmoVg of Pd/h

44 6

482 143 30

1712 42

Carbon dioxide conversion, per cent

5

18 16 6

21 8

-

'Reaclion COndMons: total flow rate = 80 rnl/min, HJCO, = 4, reaclim pressure = 10 atm. reaction temperature = 300°C

Platinum Metah Rev., 1993,37, (2) 74

Table IV

Comparison of the Reactivi of Sup rted Palladium SMAI and CI Catalysta for%enzene%ydrogenation*

Rate of benzene hydrogenation, per cenWg of Pd

696 0

66 0

498 20

599 0

Catalyst Conversion of benzene, per cent

13.5 0

1.3 0

9.8 0.4

12.0 0

1.39% Pd/Alz03 (SMAI) 1.39% Pd/AIz03 (CI) 1.50% PdiZrOz (SMAI) 1.50% Pd/zrO, (CI) 1.56% Pd/MgO (SMAI)

1.65% Pd/TiO, (SMAI) 1.65% P a 0 2 (CI)

1.56% Pd/MgO (CI)

‘Readon CondMns: inbal hydrogen pressure 30 atm. reaction temperature 140°C. reaction bme = 4.5 h. Reactor autoclave (1 70 cm’)

of SMAI and CI catalysts leads to the conclusion that the SMAI catalysts exhibit a much higher reactivity and selectivity than CI catalysts for the hydrogenation of benzene and the methanation of carbon dioxide. The highly active properties of the SMAI catalysts can probably be attributed to the presence of residual carbonaceous hgments which surround the small metallic crystallites, highly dispersed particles in metallic form and a higher degree of reduction of the

Refei 1 K. J. Klabunde, H. F. Eher, T. 0. Murdock and R

2 S. C. David and K. J. Klabunde,J Am. C h . Soc.,

3 K. J. Klabunde, S. C. Davis, H. Hattori and Y.

4 K. J. Klabunde, D. Ralston, R Zoellner, H. Hattori

5 K.Matsuo and K. J. Klabunde, J Org. Chem.,

Ropple,J Am. Chem. Soc., 1976,98, 1021

1978,100,5973

Tanaka, J C a d . , 1978,54,254

and Y. Tanaka,J C a d . , 1978,SS, 213

1982,47,843

supported palladium. However, for carbon dioxide methanation, a study of catalytic stability shows that the highly active SMAI catalysts have very poor stability compared with the corresponding CI catalysts. The explanation for the shorter life of the SMAI catalysts ranains obscure, however, it may be related to the adsorbed acidic carbon dioxide species which affect the decomposition of metallic form particles (clusters) during the reactions.

rences 6 K. Matsuo and K. J. KMnmde,J C d . , 1982,73,216 7 K. J. Kkb\mdeandY. T+J M d Cad., 1983,21,57 8 H. Kanai, B. J. Tan and K. J. Klabunde, Lungmuit-,

9 K. J. Klabunde, flmiman Me&&&., 1992,36, (2), 80

conference m, CarahFiS’; Houston, T a s , 1981, Nov. S11, pp. 83,107

11 B. A. Scott, R. M. Plecenik, G. S. Cargill, T. R. M d h k and S. R Hed, I w . Chem., 1980,19,1252

1986,2,760

10 G.ASomoriai,“- . o f d l e w l c h ~

In a continuing search for materials that combine strength, toughness and oxidation resistance at high temperatures, a variety of intermetallic compounds have been considered. A simple screening test identified aluminium- ruthenium, iridium-niobium, ruthenium-scan- dium and ruthenium-tantalum as worthy of investigation and some of the properties of these tough binary alloys were presented here in July 1992.

A further communication on the properties of aluminium-ruthenium alloys has now been

Aluminium-Ruthenium High-Temperature Alloys published (RrL. Heischer and D. WI McKee, “Mechanical and Oxidation Properties of AlRu- Based High-Temperature Alloys”, Metall. Tmns.

The authors confirm the interesting properties of A ~ . , R U ~ ~ and Al,,Ru,,Y, which combine low oxidation rates at 1 1 OOOC with good mechanical properties at room temperature. AI.,RU&~ has good high-temperature mechanical properties, and at 135OOC the oxidation rate is only marginally unacceptable, indicating that the alloy may be useful at lower temperatures.

A, 1993, 24, (3)y 759-763).

Platinum Metals Rev., 1993, 37, (2) 75

Knitted Platinum Alloy Gauzes CATALYST DEVELOPMENT AND INDUSTRIAL APPLICATION

By B. T. Horner Johnson Matthey, Materials Technology Division, Royston

The introduction of knitted catalyst gauzes into the nitric acid industry has had a major impact on both that industry and on the catalyst production procedures employed by Jdtnson Matthey It is now two years since this technological advance wasfirst reported and, because of this time interval, a summary ofprevwus work is included here to serve as a background to this significant technical progress and the commercial acceptance that has taken place over the past few years.

The production of nitric acid is achieved by passing an ammonia-air gas mixture over a catalyst and absorbing the resultant gas in water. Most indusuial plants use a platinum group metal catalyst, generally either rhodium-platinum or rhodium-palladium-platinum, to promote th is reaction. The process is carried out at temperatures in the range of 800 to 940°C and at pressures of between 1 and 14 atmospheres. In order to realise optimum performance the catalyst is usually in the form of gauze, woven from wire. This structure was developed in 1909 (l), and until very recently little change in design had taken place.

Platinum behaves well as a catalyst, and early catalyst development involved the use of pure platinum (2) a relatively weak material. Among the first alloys considered for ammonia oxidation was platinum-iridium (2) and platinum containing 10 to 20 per cent palladium. Economic appraisal of these catalysts showed that none of these alloys was suitable for use in nitric acid plants, but platinum-rhodium alloys containing 5 to 10 per cent rhodium were subsequently found to have the best combination of properties in terms of ammonia conversion efficiency and economic performance; the rhodium increasing the relatively low tensile s m g t h of pure platinum. That was 60 years ago.

Now platinum-rhodium alloys are at the heart of the nitric acid production process and as such have been the subject of much discussion. The sharp increase in the price of rhodium during

the period 1989-1991, see Figure 1, led many nitric acid producers to consider reducing the rhodium content of their catalysts. The use of 10 per cent rhodium-platinum woven 1024 mesh gauze was well established (3), however, and alloys with lower rhodium content had reduced strength and a potential for increased metal loss.

The introduction of knitted catalyst gauzes had a major impact on catalyst producers and users. The production of knitted gauze and its performance, compared with that of traditional woven gauze, is discussed here.

Rotary Knitting Machine Development

After successful commercial trials of knitting gauzes, a full-scale production system was developed (3).

The circular knitting frame on the first production machine was 76.2 cm in diameter, with

J J A J O J A J O J A J O J A J O

1989 1 9 9 0 1991 1992 YEAR

Fig. 1 The sharp increase in rhodium pr im during 198%1991 led producers to assees the rhodium content of the Mum-platinum alloy catalyst gauze

Platinum Merals Rev., 1993,37, (2), 76-85 76

Fig. 2 One of the four knitting heads on the first production machine for knitted gauze showing the clispoeition of the needles as the platinum alloy wire and polyestex carrier are eo-knitted

approximately 1990 needles around the circumference, see Figure 2, the size being determined by the need to reduce wastage and min- imise seam fabrication. Having already determined the optimum density of the cloth on the earlier development machine, the needle spacing and stitch length were maintained to achieve continuity.

Although a single feed system could probably cope with the anticipated demand, it was decid- ed that a 4-feed system would give greater flexibility. Indeed, all Johnson Matthey machines are capable of accepting 8 feeds although a require- ment for such production rates is unlikely.

The cloth is produced by co-hitting the platinum group metal wire with a multi-strand polyester yarn carrier which almost completely covers the wire and provides support during the knitting process (4), see Figure 3. The fabric is lmitted in the form of a tube then split to give a cloth 2.4 metres wide which is cut to size. The polyester carrier is next removed and the catalyst is flamed with hydrogen to activate the surface. The carrier is not removed until th is late stage of the process in order to give protection during storage; last minute cleaning also min- imises the potential for contamination by dust. Any contaminants that are present during flam- ing could diffuse into the surface of the catalyst and subsequently cause problems during use.

During the carrier removal process no residues are left behind, but its composition is such that even ifthe gauze was installed without its Temoval the catalyst would still function efficiently.

Scale-up of the development process highlighted the problem of supplying the correct volume of material, at identical rates, to each of the four knitting heads, in order to obtain a cloth of uniform tension and with homogeneous density, see Figure 4. The introduction of computer control completely solved t h i s problem. The reliability and efficiency of this knitting machine (which no longer resembles the original textile machine), together with the interest shown by customers has encouraged Johnson Matthey to

Fig. 3 The carrier is a multi-stranded polyester fibre which almost completely covers the platinum alloy wire during the knitting operation. The carrier is removed after the gauze is cut to s h e and before the catalyst is activated for uae

Platinum Me& Rev., 1993,31, (2) 77

purchase more machines for the production of knitted catalyst gauzes, as well as the catchment gauzes used in nitric acid production and in other similar chemical processes.

Industrial Application Demand for knitted gauzes from the nitric acid

industry has grown rapidly and is expanding so quickly that Johnson Matthey expects 80 per cent of its customers will have converted by 1994. It is anticipated that most catalysts which are now woven will be knitted in future. Other major catalyst manufacturers are already producing or planning to produce knitted catalysts either by rotary or flat bed knitting.

In a previous article the following list of potential benefits accruing from the use of knitted gauzes was given (2):

Increased conversion efficiency Reduced rhodium oxide formation Stronger material Greater surface area for catalysis Fabric flexibility providing greater resistance

Choice of alloy Lower stock levels resulting from quicker response times

Since then two other major benefits have been

Lower metal losses Fixtended campaign lengths.

These benefits will now be considered in greater detail to show why the adoption of knitted gauzes has been so rapid.

There are two main types of nitric acid production plants: a single pressure process performed at either medium pressure (4 to 6 atmospheres) or at high pressure (7 to 14 atmospheres); and a dual pressure process where ammonia oxidation is carried out at medium pressure, and absorption is completed at high pressure. The overall reactions are:

to damage by thermal shock

observed, namely:

4NH,+ 5 0 2 = 4NO + 6H20 2NO+02 = 2N0, ammonia oxidation

3N02 + H 2 0 = 2HN0, + NO absorption

The ammonia oxidation stage uses a catalyst pack containing up to 36 platinum group alloy

gauzes designed to optimise the efficiency of the reaction.

The whole process is fast, but a contact time of lO-'seconds is needed between gas and catalyst to maintain process efficiency. The catalysts have typical service lives of 50 to 300 days, depending mainly upon the pressure of the system.

Increased Conversion Efficiency Pilot plant trials indicated that a 4 per cent

increase in ammonia conversion efficiency was possible (3). Most industrial nitric acid plants c lah conversion efficiencies of 96 to 99 per cent, but if these figures are accurate then a 4 per cent increase in efficiency is clearly impossible. It is, however, important to appreciate that pilot plant trials only indicate potential.

The majority of nitric acid plants measure the conversion efficiency of the overall system, not of the burner. Following the installation of knitted gauze catalyst packs, detailed production information has not been made available but, without exception, all the plants have reported no drop in conversion efficiency, and some have recorded reduced ammonia usage, which indicates an improvement in efficiency. Indeed, an increase in conversion efficiency must occur because less rhodium oxide and lower impurity levels have been recorded.

Reduced Rhodium Oxide Formation Rhodium enrichment of a catalyst gauze occurs

as a consequence of the loss of platinum from the catalyst surface. Platinum oxidises and volatilises at high temperatures in oxidising atmospheres; rhodium also oxidises, but does not volatilise as readily. When a 10 per cent rhodium- platinum alloy is in use, platinum is lost at a rate approximately 19 times faster than rhodium, so resulting in a natural enrichment of rhodium. However, if the actual catalyst is PtO, and not platinum, then the need for replenishment and oxidation of the platinum is important.

When the initial composition of the gauze is 10 per cent rhodium-platinum, the final analysis of the bulk material can be 13 per cent rhodium-87 per cent platinum. An important factor in the catalytic process is the amount of Rhoz

Platinum Metak Rev., 1993, 37, (2) 78

Fig. 4 The four knitting heads are supplied with fib- at a computer-controlled conatant rate to prodnce a knitted tubular gauze, of uniform tension and homogeneow density. The 6rst production knitting machine was 76.2 c m in diameter and had approximately 1990 needlea around the circumference

present at the catalyst surface. Although rhodium enrichment is regarded as a natural phenomenon other factors also can influence its formation. For instance, if the platinum-rhodium gauzes are operated at low temperatures (< 800°C) then a decline in catalyst activity can occur. The formation temperature of Rhoz is 6OOOC and it dissociates over the temperature range 1050 to 1150°C. Poisoning causes a loss in activity which slows the kinetic processes relative to the rate of gas diffusion transfer; thus the gauze contaminated by poison, usually the lead gauze, only allows limited diffusion. Visual evidence that this is happening is the appearance of a dull patch on an otherwise bright gauze. This low operating temperature and the subsequent increase in the oxygen partial pressure stabilises the rhodium oxide, which then rapidly accumu- lates at the surface. Efforts to reduce the Rho, by raising the temperature of the gauze have only a limited success since, as stated above, the temperatures required to achieve this dissociation are high.

The structures of woven and knitted catalyst

are shown in Figure 5. The more open knitted structure achieves the same weight as the closer woven structure, due to its bulky three-dimensional nature. This open structure also offers less resistance to gas flow, which enables the reaction to take place further into the gauze and ensures a more even temperature profile across the catalyst.

This improved distribution of the catalytic activity reduces the metal loss per gauze, with a subsequent drop in the formation rate of rhodium oxide. The results given in Table I indicate significant reductions in Rhoz formation over the entire range of plant pressures, when using knitted gauzes. This is particularly significant since the major cause of campaign cessation in Example 3 (a high pressure plant) was the high levels of Rho, formation.

Another major factor contributing to the formation of rhodium oxide is the presence of contaminants, the most common of which is iron. High surface levels of iron reduce catalytic activity, promote the breakdown of nitric oxide and increase the surface concentrations of Rhoz. It

Platinum Me& Rev,, 1993, 31, (2) 79

Fq. 5 Typical structures of woven (left) and knitted (right) ga- used in nitric acid production. The more open structure of the knitted material b compeneated for by its bulky three-dimensional nature

is generally believed that the campaign life may be extended by increasing the number of gauzes in a pack, so that contamination of the leading gauzes results in the transfer of the reaction zone to a greater depth, without causing any loss of efficiency. This does not happen, however, since the ammonia is less selectively oxidised to nitric oxide; instead more is oxidised to nitrogen as the level of contamination increases.

The levels of iron impurity on the gauzes are listed in Table I. The improved gas flow through the knitted gauzes results in less solid particles being trapped and hence less Rho2 is formed due to iron contamination. Example 1 shows that there has been no drop in iron impurity levels (0.56 per cent during a woven campaign and 0.54 per cent during a knitted campaign) but the significant factor is the greatly reduced amount of impurity present on the surface of the knitted catalysts. This phenomenon is seen in all campaigns using knitted gauzes.

Stronger Material When woven catalyst gauzes are removed from

an oxidation rig they are often in a kaagile state, once the clamping supports and weights are removed. This does not occur with knitted gauzes, indeed many plant managers have commented on the catalyst integrity at the end of a campaign.

The strength of the catalyst is important, not only for high pressure plants but also for medi-

um and low pressure ones. Catalysts are designed to be supported horizontally, but in high pressure units the support basket often deforms to such an extent that the edge of the burner wall cuts into the catalyst, sometimes causing it to tear. This also happens in low and medium pressure units which usually employ rashing ring s u p port. During operation the rings may migrate to the centre, causing the catalyst to “dome”. This leaves the catalyst unsupported around its edge, which tends to result in tearing.

Tensile tests were carried out to determine the strength of knitted and woven catalyst gauzes, the results being given in Figure 6. Significantly more en- can be absorbed by the knitted structure than by woven gauze, as shown by the areas

I Knitted. /

1 4 . , , , . . . . . . ‘ I 10 20 30 40 % 60 70 80 90 1 0 0 110 120

DISPLACEMENT, mm

Fig. 6 Strips of knitted and woven gauze (25 mm x 180 mm) were subjected to tensile testing, with constant gauge length and cross-head speed. The knitted alloy was found to absorb mreenergy. Bothgau~osare 10 percent rhodium-platinum, 0.076 mm diameter wire; the gauze is 1024 mesh or equivalent


Table I Example 1: Low Pressure Plant

Knitted trial 1 Knitted trial 2

Typical woven gauze pack 3

Rhodium Impurity Impurity in Total kl surface, I on gauzes, 1 catchment. I impurity Gauze Platinum Rhodium per cent per cent per cent per cent

89.31 10.64 8.9 0.05 0.05 0.1 16 89.18 10.78 12.1 0.06 0.48 0.54 0.115

88.31 11.33 18.7 0.36 0.2 0.56 0.112

Metal loss, gramshonne

of acid produced

Woven Knitted Knitted )latinurn

Iron, per cent

0.2 0.2 0.1 0.1 0.1

trace 0.3

10% rhodium-platinum 5% rhodium-platinum

Rhodium, Iron, Rhodium, Iron. per cent per cent per cent per cent

28 0.1 10 trace 27 trace 7 0 25 0 8 0 30 0 8.5 0 32 0 8.7 0 32 0 10.0 0 34 0 10.0 0

5 6 7 8

Gauze number

76 75 68

1 2 3 4 5 6 7 8 9

10 11 12 13 14 15 16 17

0.1

Surface levels of rhodium oxide TvDe of aauze and Dosition in Dack

31 0 11.0 0

Woven 10% rhodium-i

Front 29.7 36.3 37.2 43.2 46.9 51.5 55.0 58.8 60.5 61.4 60.5 63.6 63.1 62.1 63.6 59.2 56.4

atinurn Back 38.2 59.9 61.9 66.0 63.8 63.6 62.5 63.8 61.3 65.9 64.9 61.3 65.1 64.3 64.5 60.0 54.3

Knitted 10% rhodium

Front 20.1 19.1 21.2 15.5 14.8 15.2 19.9 21.7 14.6 12.4 12.8 13.3 13.6 11.7 12.9 12.8 14.2

'latinurn Back 14.6 13.8 14.3 11.1 12.6 15.5 17.5 19.2 13.1 12.9 11.4 11.7 12.1 12.2 11.7 13.1 14.2


Example 2: Medium Pressure Plant

Rhodium, per cent

10 7 8

8.7 10.0 10.0

I 11.0

8.5

~~

Levels of rhodium and iron at the surface of the gauze

I 1

Woven

Rhodium, Der cent

Gauze number

56

61 62 68 76 75 68

58

)latinurn

Iron, per cent

0.2 0.2 0.1 0.1 0.1

trace 0.3 0.1

)e of aauze and comDosition

Knitted I Knitted 10% rhodiun

Rhodium, per cent

28 27 25 30 32 32 34 31

Aatinum I 5% rhodium-Dlatinum

Iron, Der cent

0.1 trace

0 0 0 0 0 0

Iron. Der cent

trace 0 0 0 0 0 0 0

Gauze type

Knitted trial 1 Knitted trial 2

Typical woven gauzepack 3

Woven 10% rhodium-olatinum

Example 3: High Pressure Plant

deliberately introduced into the knitted gauze with the aim of making the fkacture occur within the gauze length, but without success. A simple analogy is to try tearing a knitted jumper compared to tearing a woven shirt.

Greater Surface Area for Catalysis The knitted gauzes have more surface area

available for catalysis because of their bulky three- dimensional structure. In woven gauzes the potential area for catalysis is masked, when compared to the knitted structure. Mathematical modelling was used to estimate the surface area available for catalysis for both types of gauze, and values of 83 per cent (1 7 per cent masked) for woven and 93 per cent (7 per cent masked) for knitted gauzes were obtained. In knitted gauzes the gas circulates around the wire, which provides more active sites for catalysis. This increases the potential for oxidation and reduces localised metal loss (wire thinning), so the wire retains its strength, which results in a longer life.

Fabric Flexibility The flexibility of the knitted structure allows

the catalyst to remain essentially fluid when subjected to start-up and shut-down procedures.

Fq. 7 A tensile test sample of knitted gauze stretched siflcantly before hacture, which u ~ d y occurred at the clamping jaws

under the two curves. This is further illustrated in Figure 7; Figure 8 shows almost instant tearing of the herringbone - the strongest of all the conventional weaves -which results in rapid failure. A knitted sample stretches considerably before hcture, which usually occurs at the clamp is coosidered interface and not within the gauze length- Flaws to be one of the strongest conventional weaves, a ten- of different types, such as holes and cuts, were sile test sample tore aihrost instantly when under load

Platinum Merals Rev., 1993, 37, (2) a2

Fig. 8 Although the henhgbone structure is coosidered to be one of the strongest conventional weaves, a tensile test sample tore almost instantly when under load

When in use the catalyst gauze is held rigidly in a burner, but some distortion occurs with temperature change. The catalyst will contract or expand, which may cause deformation andor tearing at the edges; if this does not happen the gauzes may slip from under the clamp allowing ammonia to by-pass the gauze. The flexible nature of the knitted gauze enables the metal to expand and contract readily without affecting its physical and catalytic properties.

Gauze No. 3 woven standard

Choice of Alloy Historically the conventional alloy for ammo-

nia oxidation has been 10 per cent rhodium-platinum woven gauze. Before weaving can commence on a loom between 50 and 100 kg of wire must be available, whereas a knitting machine only needs 5 kg of wire. This permits a more flexible approach to alloy composition and also allows a faster response to market changes. There are now four standard alloys in production: 5 per cent rhodium-platinum, 8 per cent rhodium- platinum, 10 per cent rhodium-platinum and 5 per cent rhodium-5 per cent palladium-platinum.

Removal date Acid production Metal loss Metal losshonne of acid produced Surface rhodium

Lower Stock Levels Due to the different alloys which can be

accommodated and the reduced amount of wire required for start-up, the production of large quantities of “stock” catalysts has not been required, despite the increase in the number of alloys being supplied. It also follows that a

quicker response to a request for any lmitted alloy is possible. Knitting can commence as soon as wire is produced. Certain non-standard alloys have been and can be produced to suit particular customer requirements.

Lower Metal Losses The actual nature of the metal lost from cat-

alysts has been the subject of speculation for a number of years. There appear to be two main types of metal loss: platinum volatilisation and mechanical removal. The platinum which is lost as Pt02 can be collected by installing palladium- based catchment systems, which can recover up to 95 per cent of the total platinum losses. Platinum is also lost by mechanical removal caused by vibration during plant operation, and this can be further compounded on start-ups and shut-downs. There may also be temperature differences in a catalyst bed which can result in increased losses.

The general conclusion from many studies is that volatilisation is the main contributor to platinum loss (3, 5-7). In order for platinum to be volatilised it must come into contact with oxygen molecules; therefore volatilisation is dependent upon the conversion of ammonia and hence on the production of acid. Assuming constant conversion efficiencies, the metal loss should be fixed and therefore the only possible reason for reduced metal loss must be smaller losses due to mechanical removal.

Table It

m i c a l Production Data

Gauze No. 2 knitted

Removal date Acid production Metal loss Metal losshonne of acid produced Surface rhodium

31.1 2.90 11345, tonnes 20.07, per cent 0.032, grams 14.2, per cent

31.1 2.90 11345, tonnes 21, per cent 0.042, grams 34, per cent

Platinum Metals Rev., 1993, 31, (2) a3

Fig. 9 After use for ammonia oxidation both woven and knitted gauzes Show rea~ucturing of the surface. Fragile “cauliflower” like formatiom grow on both typea of cadyst but on knitted gaweu the struchmd rearrangement is widely clispersed throughout the catalyst pack l e a d q to a more even temperature distribution, lese mechanical damage and reduced metal loss, compared to the woven gauze

Metal losses from woven and knitted catalyst gauzes per tonne of acid produced are shown in Table 11. The differences in metal loss can be partly explained by the restructuring that takes place on all gauzes, see Figure 9. The cauliflower- like formations that grow on the catalyst are very w e , and become more so with increasing s k y clearly, the more fragile the structure the greater its susceptibility to mechanical damage. With knitted gauzes there is widespread structural rearrangement throughout the catalyst pack and therefore less susceptibility to mechanical damage. This widely distributed restructuring also leads to a more even temperature distribution, and the increased structural flexibility enables it to withstand thermal shock more readily, which accounts for the reduced metal losses.

In some industrial plants, however, little or no reduction in metal loss has been seen, and therefore it can be concluded that these plants do not experience any significant loss of metal by mechanical removal.

Extended Campaign Length One of the main requirements in ammonia

oxidation plants is long catalyst life which permits extended campaign lengths. There are three factors affecting the catalyst life: material slrength, rhodium oxide formation and contamination. Improvements in all these area have been observed as a result of using knitted gauzes. Various types of plant are now running extended campaigns. Typical examples are:

Low Pressure Medium Pressure High Pressure When ammonia oxidation plants are running

they are reasonably cost effective and reliable, but shut-downs to change the catalyst are cost- ly in terms of both money and manpower, and

from 180 to 240 days from 120 to 200 days

from 50 to 80 days

Platinum Metals Rev., 1993, 37, (2 ) a4

invariably cause other problems of a mechanical nature. For a medium pressure plant, it is estimated that having one less change in the yearly schedule can result in a saving of E60,000 on the metal costs alone.

Summary Knitting is rapidly gaining acceptance as

a gauze manufacturing technique, and material fabricated in this way is also being applied to areas other than nitric acid production.

Samples of knitted platinum group metals have been supplied for various specialist applications and to industries that deal predominantly in base metals.

Many of the early claims made for knitted catalysts have now been substantiated and, indeed, many other beneficial and unexpected results have been achieved. Further developments in the knitted structure and in the alloys involved are continuing, and the future for knitted gauzes looks assured.

References 1 K. Kaiser, German Parent 271, 517; 1909 4 Johnson Matthey PLC, European Patent 2 S. L. Handforth and J. N. Tilley, Id. Eng. Ind.,

5 H. Connor, PZaitzumMetolsRev., 1967,11, (2), 60 3 B. T. Horner, Plutinum Metals Rev., 1991, 35, 6 H. H O ~ ~ Y Chem.-lng.-T'Jb 1967,399 (21~89

7 H. Holrmann, I%aina Meralc Rev., 1969,13, (l), 2

36% 153B 1934 26, (12), 1287

(21, 58

Some Diverse Aspects of the Platinum Metals Noble Metals and Biological Systems: their Role in Medicine, Mineral Exploration, and the Environment

EDITED BY R R BROOKS, CRC Press, Boca Raton, 1992,392 pages, ISBN 0-8493-6164-8, U.S. $156, E94.50

The rise in interest in environmental issues over recent years has resulted in a significant increase in the number of papers related to the investigation of the distribution of materials in the environment, and particularly in biological systems. The above named book offers an extensive review of this literature in relation to gold, silver and the platinum group metals, with particular emphasis on exploration and medicinal use.

Because the noble metals occur at low concentrations in the earth's crust, trace analytical techniques are required for much of this work, and therefore the book begins with a chapter on the analysis of noble metals. This review is necessarily brief but highlights the improvements that have been made in recent years through the introduction of neutron activation analysis and inductively coupled plasma techniques, with emission or mass spectroscopy detection.

Much of the information g a t h d for this book deals only with silver and gold, due to their generally higher concentrations in the environment and their longer history of interest fkom exploration studies. Details and particularly interpretation of data on the platinum group metals is thus limited.

Two chapters discuss the determination of noble metal concentrations in biological mater-

ial as an aid to mineral prospecting. Plants and microorganisms concentrate the noble metals fi-om the soil, allowing evidence of underlying mineralisation to be obtained. Biological mobil- isation of noble metals by microorganisms is reviewed as is the relationship of animals and noble metals. This section is then summarised by a general discussion of noble metals in the environment.

The final part of the book, consisting of four chapters, deals with the role of noble metals in medicine. The use of gold therapy for arthritis and platinum-based chemotherapy for cancer is now well known and, although the reviews are well written, the interested reader will probably be aware of th is material already, or wish for a more detailed study as provided in numer- ous other specialised texts. Other chapters in this section deal with the use of osmium compounds in arthritis and ruthenium compounds for cancer therapy.

For those who have considered the role of noble metals in the environment and their interaction with biological systems, this volume should provide something of interest. It offers a guide to some of the less well known literature on this subject matter, much of which was originally published in Russian. C.F.J.B.


4 Johnson Matthey PLC, European Patent

5 H. Connor, PZadtzumMnOlsRev., 1967,11, (2), 60 6 H. Holzmann, Chem.-Zng-Tech., 1967,39, (2), 89 7 H. Holrmann,I%ainaMeralcRev., 1969,13, (1),2

364, 153B

The Modification of Superconductors PLATINUM GROUP METALS CONFER NOTABLE PROPERTIES

By Yu. M. Shul'ga, E. N. Izakovich, Y I. Rubtsov and B. E Shklyaruk Russian Academy of Sciences, Institute of Chemical Physics, Chernogolovka, Russia

Since the discovery of the f irst high temperature superconductor, YBaCuO, m a n y attempts have been made to improve i ts properties by the addition of modijiers; indeed almost all of the elements in the Periodic Table have already been tried in this w a y The present survey, covering both our own work and the published literature, examines the effects of adding the plat inum group metals to the superconductor, resulting in the formation of several new compounds, many of which are semiconducting and some of which may have potential value in engineering and chemical technoloa. The complex oxides formed are characterised and data on the superconducting properties of the modijied Y B a C u O oxide phases are presented.

Immediately after the discovery of high temperature superconductors (1) a series of papers appeared discussing their modification by other metals; now almost all the elements of the Periodic Table have been used as modifiers. The aims of this research were as follows: to produce a modification-induced increase in the critical temperature (TJ, to verify the hypothesis on the mechanism of superconductivity by substituting atoms of one type for those of another, to find the effect of additions to the initial mixture on the size of the particles formed, and to increase

the rate of formation of the main phase, for example, Y€3a2Cu 307-s.

The high reactivity of the components in the superconductor cause it to react with the container material, forming new phases which affect the properties of the superconductor. Such phenomena, observed for the YE!a2Cu307-s + platinum metals system, were discussed recently (2). In this review we present data from the literature and from our own work on the interaction of YBa,Cu,O,, with all the platinum group metals; and new phases containing platinum metals are characterised.

i i 6 6 lo -i2 i9 is NUMBER OF CYCLES

Fig. 1 The dependence of T-, the onset of the superconducting transition temperature, on the number of cooling-heating cycles for Y B a l l ~ O , ~ (sample No. 9, see Table I) is shown. From the m u d cycle onwards T. for cooling and heating coincide

The YBa2Cu307-a + Ruthenium System (3)

Compounds of the platinum group metals are known to be catalytically active for redox reactions, with ruthenium exhibiting the highest activity towards inorganic ions (4). In the absence of ruthenium, the synthesis of YBazC~307-a usually takes place at 92&95OoC and requires about 60 hours (5). However, the Y-Ba-Cu-Ru-0 system is characterised by two peculiarities: a short- ening of the synthesis time of YBa $& 3O7-8, by a factor of approximately six, and a decrease in the reaction temperature to 88OoC, which can be

Platinum Metals Rev., 1993, 37, (2), 8 6 9 6 86

c Sample number

1 2 3

4

6 5

7

9 8

10 11 12

13 14 15 16

explained by assuming that ruthenium a m as a catalyst for the synthesis. It should be noted that an increase in the duration of the synthesis causes degradation of the superconducting properties; thus, sample No. 15, whose composition is presented in Table I, required 10 hours to sinter, whereas sample No. 16 took 26 hours.

From Table I it may be seen that certain specific ratios of barium, ruthenium and copper are required to produce materials having a high superconducting mansition temperature, T, (see sample Nos. 2,4,6-9 and 11-15). The appearance of a superconducting phase with a lower T, is characteristic of samples Nos. 1, 3, 5, 10 and 16. Samples containing more than 0.5 moles of ruthenium per mole of yttrium loose their superconductivity. Thermal cycling of samples with high T. results

in hysteresis for practically all of these sintered samples after the first cycle (293-77 K and 77-180 K), the T, being 94 K on cooling and 107 K on heating. No hysteresis arises during

I R u ~ BaSu, Tc(R),K Tc(X).K

T, TC T O O I Tco, Too,

B&Cus 89 - 54 12 2 0.1 B&Cuzo 100 95 91 78 22

- 48 15 8 Ba, 8Cu3 -

B&CU, 8 95 92 88 85 68 Bar &u2 - - 77 18 5 Bar 8C~2p 94.5 93 86 78 47 Bar 8C~ra 95 92 92 75 59

B G u r 88 83.5 86 46 8 Ba, sCus 94.5 94 92 86 69

B&Cus 85 - 69 64 7 0.4 B&Cuzs 99 94 87 62 9

Bar 8Cu3 97.5 96 88 81 60

B&Cus 92 88.5 87 29 5 B & C U ~ ~ 90 89 88 71 16

0.5 Ba, Gus 94 93 89 88 77 Ba, scus 90 77 79 66 11

0.2

0.3

further cycling; T, first increases, then gradual- ly decreases (see Figure 1) before becoming stable at 94 K after the 17th cycle. Storing the samples in liquid nitrogen (6), as well as thermal cycling (7), is known to increase T,, which may be caused by some micro- or macrostructural phase transformation up to the quasiequilibrium state.

Samples with T, higher than the liquid nitrogen temperature were studied by X-ray phase analysis. Samples containing 0.1-0.7 moles of ruthenium (per mole of yttrium) appeared to be two phase (Figure 2a), the YBazCu30,.s phase was superconducting, while the other ruthenium-containing phase exhibited semiconducting behaviour. In the sample with a ruthenium content of 0.8 moles only the semiconducting phase was found to be present. Unit cell parameters are listed in Table II. When the ruthenium content was above 0.9 moles (per mole of yttrium) the sample was multiphase. However, the samples are superconducting, see Table 111 when the


Table I Superconducting Properties of yBa,Cu,Ru.O,A

0

0

O X 0

x x x x

d,nm I , per cent

0.2836 1 00 0.2700 43 0.2076 33 0.1470 19 0.1315 16

28, d e g r m

d,nm

0.2735 0.2333 0.1580 0.387 0.1363

Fig. 2 (a) The diffractogam of YBalrCur.,RUuO,~, where o is YBa,Cu,o,4 and x is Y,B&uRuZOl,, and (b) the diffrac- togram of YBa,cuJtlluo,

ratio of the intensities of the main peaks on the X-ray dfiaction pattern of the sample under study of the superconducting, Z&Zm non-superconducting (semiconducting) phases, is above 0.485. This provides evidence for the existence

of a “percolation limit” in the superconducting phase contents, below which superconductivity is not observed. This may be interpreted in terms of the infinite three-dimensional cluster (8) of Josephson junctions (9).

Using X-ray microanalysis the composition of the semiconducting ruthenium-contahhg phase, for all samples with ruthenium contents less than 0.9 moles was found to be YzBa,CuRuzO,. But in the sample with ruthenium content of 0.8 moles, only this phase was found to be present. The compound is brown in colour and its melting point was found by thermal gmvimetric analysis to be 1090OC. The valence states of ruthenium and the other elements were examined by X-ray photoelectron spectroscopy (XPS). The peaks of the elements contained in the Y-Ba-Cu- Ru-0, system are shown in the wide-scan spectrum, see Figure 3, where data for all the systems under investigation are summarised.

The oxidation state of the ruthenium on the surface of Y-Ba-Cu-Ru-0 samples can be evaluated h m the dependence of Eb(Ru3d,), where Eb is the binding energy, on n (1 0), where n is the coefficient in RuO.. However, before the localisation of the Ru3dvz, and the Ru3d line intensities, it is necessary to distinguish between the contribution from the Ru3d and Cls lines. The carbon may result kom surface contamination, residual gases in the vacuum system, non-

Table II

Measured Values of the d Spacing and Intensities, I, of the Major Peaks on X-ray Diffraction Patterns of Superconducting YBa2CuJ0,&) and

Semiconducting Ruthenium Phases (II)

I , per cent

100 40 31 25 18

88

Sample number

1 2 3 4 5 6 7 8 9

10 11 12 13

Table 111

Parameters of the Ruthenium-Containing Samples

Composition T C

97 97 95 97 96 90 99 97 94 - - - -

96.5 95 92 96.5 95 89 94 96 93 - - - -

L(0.2836 nm) L(0.2735 nm)

5.65 4.4 2.1 8 1.79 1.4 1.135 0.86 0.68 0.485 0.39 0.295 single-phase multiphase

reacting part of the starting powders, and so on, which overlap in the XPS spectrum for Y-Ba- Cu-Ru-0 samples, Figure 4. For th is purpose the intensity of a non-overlapping line, Ru3p, and the ratio Ru3p:Ru3d have been determined for Ru02 powder. The Ru3p:Ru3d ratio measured coincided with the value calculated to an accuracy of 3 per cent (1 1). In the case of RuO, it was not difficult to estimate the separate Ru3d and Cls contributions, since the most intensive

peak, R3dsa, did not overlap with the Cls spectrum, Figure 4.

The R~3d , ,~ peak position (284.7 ev> for two Y-Ba-Cu-Ru-0 samples provides evidence for the high oxidation state of the ruthenium atoms. The value for Eb(Ru3dsn) is 283.2-283.6 eV for RuO,, depending on the calibration method (1 0). Such high values of Eb(Ru3dY2) were obtained in the Y-Ba-Cu-Ru-0 samples for which the values Of Eb(Ol.9) and Eb(CU2pwz) Were Usual, that is,

UI - .- s ri b i 0

m 3 K

2 :: 3

Y Fq. 3 Wide-scan X-ray photo- z electron spectra of the Y-Ba-Cu- 6 M - 0 eamples, where M is a platinum group metal (aee Table 3 IV), (showing photoelectron g intensity diatribution against bmding energy)

500 0 lo00 500 0 BINDING ENERGY, eV

Platinum Me& Rev., 1993,3?, (2) 89

YBa1.8C~2.0R~0.107d YBal.8C~2.0R~l.607d Y Bal.eC~2.sR~o.207-s Y Bal.sC~2.0R~0.207d Y BazC~z7R~o.307-s YBazCu2sRuo.sOs Y B&Cuz.sRuo.D-s YBa,.sC~3R~o.4L+a Y Bal.sC~3R~0.60~+a Y Bal.aC~3R~o.,0s Y B&CU~RUO.&~ Y BazCu3Ruo.sOo~ Y B & C U ~ R U ~ . ~ O ~ O ~

293 289 2e5 281 277 BINDING ENERGY, eV

Fig. 4 X-ray photoelectron spectra of ~ ~ , C U , ~ R U , . , O ~ - ~ (I) and RuO, (11), within the Ru3d + Cls range

coincident with those for YBazCu307-s (12-14). Consequently, the oxidation state of ruthenium in the compositions under consideration is high, Run’ being most probable. Therefore, the final composition of the ruthenium phase may be represented as YzBa,CuRuzO,, (3, 15), a compound of sufficient stability under high

In Table lV the bulk and surface compositions of the samples are given, the surface composition being determined from the following formula:

vacuum.

where [C.] is the concentration (in atomic per cent) of element x, I is the integral intensity of the analytical lines and (T is the photo-ionisation cross-section. The summation was performed along the analytical lines for the metals. A comparison of the bulk and surface compositions showed that the surface of all the samples in the Y-Ba-Cu-M-0 system, where M is a platinum p u p metal, was barium enriched, as in the case

of YBazCu3074. (The Ba3& line of relatively low kinetic energy, about 470 eV, was taken to be an analytical one). The coefficient, y, where yx = [CX]”/[Cx]”, is presented in Table IV for the platinum group metals which, in our opinion, are the most interesting. (Values of [C.]“ were obtained by X P S , while values of [C,]” were obtained by chemical analyses).

The elements of the platinum group may be divided into three sub-groups: ruthenium and iridium, with y much greater than 1, constitute the first sub-group; the second sub-group contains platinum, rhodium and osmium, while palladium is the only representative in the third sub- group with y = 0, even at very high palladium concentrations.

Considerable enrichment of the surface by a modifying agent may take place when it is not incorporated into the lattice of the main crystal phase. When YBazCu307-6 is the main phase, the presence of a platinum group metal, My does not decrease the T. value, as shown by the measurements of the temperature dependence of the magnetic susceptibility, and as observed for the ruthenium containing samples.

The YBa2Cu30,-a + Rhodium System Like ruthenium, the other platinum group

metals are catalysts for the synthesis of YBazCu3074, which is shown by a faster reaction, the absence of a “green” phase, (Y2BaCu05) and a decrease in the reaction temperature.

The YBB~CU~O~.~ + rhodium system is very similar to that containing ruthenium, that is, its T, is dependent on the ratio of the components. The presence of only one rhodium-containing phase, Y,BaloCuRh,O,, is characteristic of the system (X-ray microanalysis data). The results of the X P S study of th is compound are presented below, its wide-scan spectrum being shown in Figure 3.

The Rh3dsn peak, which is the most hquent- ly used analytically for rhodium compounds, is easy to distinguish in the X P S spectrum of the Y- Ba-Cu-Rh-O composition. Its position at 309.4 eV is evidence for rhodium being in the 3+ oxidation state in the oxide matrix (1 6). It should be noted that the “typical” value of &(Rh3&) for

fieinurn Met& Rm., 1993, 37, (2) 90

Table W Bulk and Surface Compositions of Samples from

the Y-Ba-Cu-M-0 System, where M is a Platinum Group Metal

Sample

YBaCuz ~RuosO.' YBaZCu2 2Ru0 Y Ba2Cu,Rho ,O;

YBa&u,Pd 030X. YBa,Cu,Pd, 30.CI,"

YBazCu3PdomO.

YBazCuaPdoeO, Y BazC~jPdzO~ YBa2Cu30sO,O.'

YBa,Cu31ro 70.' YBazCu,Pto7O.'

Y z B ~ ~ C ~ z 0 ~ 0 i o . i

YzBa~c~zPtOio

Composition, at.%

Bulk

Y Ba Cu M

17 17 15 17 16 16 15 12 15 25 15 15 25

33 33 30 33 32 32 30 25 30 37 30 30 37

45 37 45 49 48 48 44 37 45 25 45 45 25

5 13 10 1 4 4

11 25 10 12 10 10 12

+he wide-scan X-ray photoelectron spectrum of the sample 1s shown on Figure 3

the Rh3+ complexes is 310.7 eV. However, the value of 308.9 eV has been reported elsewhere for the Rh,o, oxide (1 7).

Thus, the formal oxidation state of the rhodium modifyins agent in the Y-Ba-Cu-Rh-0 samples is 3+, however, the positive charge on the rhodium atom in the sample studied is notice- ably higher than for Rhzo,. These data allowed the refined formula of the rhodium phase to be determined as Y3Ba,oCuRh,02,.

The YBa,Cu,O,, + Palladium System The modification of the YBa zcU,o7.& system

by palladium of more than 0.001 atomic per cent results in the complete loss of superconductivity (18, 19). In subsequent literature palladium has been shown to substitute for copper in the superconductor lattice, forming YBaZCuz.,P&.,O7 (20). The absence of palladium on the surface of the Y-Ba-Cu-Pd-0 samples with high palladium contents is evidence of this (Table IV, XPS data), the copper content being somewhat increased (when compared with the other sam-

Surface

Y Ba Cu M

19 23 24 24 18 16 20 23 20 14 25 23 32

42 41 38 38 39 46 48 26 40 46 42 40 36

31 13 28 38 43 38 32 25 30 32 16 23 21

8 23 10 0 0 0 0

26 10 6

17 13 11

1.6 1.8 1 .o 0 0 0 0

1 .o 1 .o 0.5 1.7 1.3 0.9

ples containing the same amount of modifying agent M) .

Of the samples in the Y-Ba-Cu-Pd-0 system studied, only No. 8 had sufficient surface concentration of palladium to difFerentiate the Pd3& peak fhm the XPS background noise (Table IV). The &(Pd3d,,J value of 336.6 eV is evidence that the palladium oxidation state in the undersurface layer is 2+. For PdO the value of Eb@d3dw2) i s 336.5 ev (21), which is almost the same as obtained in our measurements.

Nevertheless, it seems unreasonable to expect the oxidation state of the promoting element to be the same as in sample No. 8.

By means of X-ray microanalysis three new phases were detected in the YBazCu3Pdz0,, sample annealed at 900OC.

The YBa2Cu30,-, + Osmium System This system was studied as thoroughly as that

of ruthenium. A series of YBazCu,Os,O, samples (with x = 0.1-1 .O) was synthesised according to the procedure described in (3).


NO.

- 1 2 3 4 5 6 7 8 9

10 11 12 13

TEMPERATURE, K

Fig. 5 The temperature dependence of magnetic susceptibility in YBa2Cu,0s,0, where x = 0.14l.8

All the samples, are multiphase compounds. In samples with x = 0 . 1 4 8 two superconducting phases are distinguishable, one having T. = 93 K, while the T, values of the other phase may vary from 62 K to 83 K (Figure 5). Samples with x = 0.9 and x = 1.0 are not superconducting. The XPS method was used to determine the oxidation state of the osmium (see Figure 3 for the

151ip , , , m

0 2 4 6 e OSMIUM OXIDATION STATE, n

Fq. 6 The dependence of the bmding energy Eb(&4f7n) on the osmium oxhbtion state n, in metal oomplaea The Eb(Os4f,o) dues for complex 2 - &[Os(CN),].4Hz0 and 5 - ~owI(pmeshu are talcem (22) and (2%

wide-scan spectrum). Since there is no information in the literature on the dependence of the most intensive osmium peak, 4f?izy on the osmium oxidation state, our data in Figure 6 may be of interest. The Eb(Os 4fin) values were found to be 53.5 and 54.3 eV for samples with x = 0.7 and 1 .O, respectively, which correspond to 0 s " ( x = 0.7) and 0 s " (x = 1.0). The osmium 4 j h e shape (a larger half-width) is evidence for the presence of states other than the main states of the osmium atoms in the sample under study (Figure 7).

X-ray phase analysis showed that samples with x = 0.1-0.8 consisted of the main phase: YBazCus07-i-s (Pmrnm, a = 0.3882, b = 0.3891, c = 1.1688 nm for the sample with x = 0.7), and an admixture phase: BaOsO, (InSm, a = 0.935 nm) (see Figure 8). Copper oxide and unidenti- fied compounds with diffraction peaks at d = 0.4833 and 0.4187 nm were also detected among the admixtw S.

The data &om X P S and X-ray phase analysis may lead to the conclusion that the compound with four-dent osmium, BaOsO,, is formed in samples with x = 0.1-0.8, see Table V.

The non-superconducting samples, with x = 0.9 and 1.0, consist of two unknown osmium phases (as the main components) and a small amount of YBazCu,07-s, Y,BaCuO,, BaCuOz

1 '.- 60 56 50

BINDING ENERGY, eV

Fig. 7 X-ray photoelectron spectra of the YBa,Cu,Os,.@, solid line, and metallic osmium, dotted line

Platinum Metals Ren, 1993,31, (2) 92

Fig. 8 X-ray powder diffraction patterm of YBa,Cu,Os.O, for osmium eontent r = 0.147, where o is YBa2Cu,07-~ and x is BaOsO,

F I

20 30 40 60

20, degrees

Obtained

d, nm I, Yo

0.2957 100 0.2090 46 0.1 706 52 0.1321 18

and YzCu20s. The unknown phases were iden- tifed as Y2Ba,CuzOsOz and YBa3Cu40so,,0x by X-ray microanalysis. Since the oxidation state of osmium in samples with x = 0.9 and 1.0 is 5+ (XPS data), the phases may be presented as YJ%~,CU~OSO,~.~ and ~ 3 C U 4 ~ 0 . 1 0 & & Attanpts to synthesise the phase Y2Ba,CuzOs010.s in its pure form were a failure and gave a mixture of compounds, such as YzBaCuOs (Pbnm; a = 0.7131, b = 1.2164, c = 0.5657 nm), BaCuOz (Tm3m, a = 1.8294 nm), and Y2Cu205. The other &&on peaks in the XRD pattern of this sample were attributed to the Y2Ba,Cu20s(V)0,0.s phase (Table VI). The synthesis of the other o h -

Ref. 24

d, nm I, %

0.2961 100 0.2078 10 0.1 708 50 0.1325 50

Table V

XRD Data of BaOsO, (24) and the Osmium Phase

in YBazCu,Os~,Oy

25 1 00 30 20 25 10 50

0.4810 0.41 32 0.3101 0.3013 0.2953

um phase, YBa3Cu40so.10,s, was not a success either. X-ray phase analysis showed the presence of YBazCu30,-s, BaCu02 and YzBaCuO,. The XRD data on the fourth phase are given in Table VI. They were thought to belong to YBa ,CU~OS~.~ (V)Os+s.

The YBa2Cu& + Iridium System This system is a close analog to the ruthenium

and rhodium systems. The dependence of T, on the ratio of the initial elements was also similar to

Table VI

Data on the X-ray Phase Analysis of Y&3aSCuzOsO, (I)

and YBasC~OsR108+a (II)

dab., nm

7.998 4.800 4.132 4.004 3.71 8 2.901 2.346

I,%

7 5 9

20 100

Plutinum Met& Rev., 1993,31, (2) 93

that of the ruthenium system (see Table I). X- ray phase analysis and X-ray microanalysis detected only one iridium compound in the system, which appeared to be Y3Ba6Cdr60,, with a face centred cubic F-cell (a = 0.8341 nm).

According to the X P S data the Eb(h4&) value for the Y-Ba-Cu-Ir-0 sample is 63.2 eV. It should be noted that the Eb(Ir4f,,2) values obtained for KJrCI, and K21rCI, complexes are 62.6 and 63.7 eV, respectively, (1 6) and the E @4f7J value for the main state of the I r / A 1 2 0 3 catalyst stored in air is 62.5 eV (25), and it was thought that the main iridium state on the catalyst surface was IrM (25). Therefore it may be expected that the Ir4+ oxidation state is highly probable in the Y-Ba-Cu-Ir- 0 system, at least in the undersurface layer. It is also noteworthy that the Ir4fline of the sample is rather narrow; consequently iridium is included in the composition of only one compound on the surface, which agrees with the X-ray microanalysis data. A high coefficient of surface enrichment, 'y, with iridium may lead to the supposition that the size of the iridium containing particles is smaller than that of the main phase present, namely YBarCu307_6.

Thus, from the above data the iridium compound Can be representeed Bs Y3Ba&Uh&.,.

The YBa2Cu307-, + Platinum System This system has been studied in the greatest

detail, and was considered in (2), and results of the X P S study are described here.

The main state of platinum in samples of the Y-Ba-Cu-Pt-0 system was found to be R4', since measurements gave Eb(F't4f7J = 74.4 eV, which is closer to 74.5 eV for PtOz than to 73.7 eV for PtO (26). However, considerable shoulders were seen on the Pt4fspectrum in the region of higher binding energies (Figure 9). At present it is difficult to find an unequivocal explanation of this phenomenon, although we considered two hypotheses: first, the influence of the Ka3,4 satellite of the Ba4d line and second, the presence of platinum ions in an oxidation state higher than 4+.

A careful examination of the spectral site of samples not containing platinum shows that the Ka3,* satellite of the Ba4d line does overlap with

:w ,I -. do 80 70

BINDING ENERGY, eV

Fig 9 X-ray photoelectron spectra of YBa2Cu,07A, dashed line, and YBatCu,PLO., solid line, within the Ba4d + Pt4f range

the Pt4fspectrum. The line shape of the Pt4f spectrum is very dependent on the PcBa ratio, so that at low values of the ratio the height of the Pt4fwz peak may be greater than that of the R4hn peak. It should also be noted that the shape of the Ka,,* satellite of the Ba4d line is rather smooth, and it seems impossible to explain the shoulder in the spectrum Pt4f (marked * in Figure 9) only by means of the contribution of this satellite. We now attribute this effect to the presence of Pt". However, we have not succeeded in observing this effect on the spectrum of the known Y2Ba3Cu2Pt0,, (27), which is evidence for the presence of as yet undetected phases with Pt6+ in the YBazCu307_s + platinum system.

Conclusion The following generalised conclusions have

been made from the data considered here: Superconductivity in YBa2Cu30F6 + M, where

M is a platinum group metal, depends on the amount of M in the system, the lowest values being characteristic of systems with palladium, which substitutes for copper in the superconductor structure. The highest amounts of M have been found for the osmium system, barium osmate being formed in this case. All platinum metals form new non-superconducting (semiconducting) phases, listed in Table W.

As seen from Table VII, ruthenium exhibits the highest oxidation state of 8+ in this compli- cated system, the existence of a Pt" compound

Platinum Me& Rev., 1993,31, (2 ) 94

Table VII

I

Composition valency X-ray data I References

YBa5CuRuzOn Y3Ba,oCuRh0, YzBaPd05

Nd2BaPdOs Y BazC~2.5Pd0.507

Y2BazCuPtOa

ErzBa,CuPtOa

HOzB&CUPtOa NdzBaPt05 YBazrCuo.zPtOs

Y2(Ba, Sr)2SrPtCu20,0

La, ,CaoBas7CuzaPt,O, ErBa, .aCuo.nPto a04.u

B&Pt&J&e (X4.5) La,.5Sro.5Cuo.75Pto.~04

LnBa,Cu,Pt,O,(Ln = Sc. Y, Pr, Nd, Tb, Tu, Yb, Lu) Er3BasPt4Ol7 Y b3BaBPt4Ol7 Tm3Ba8Pt,0,75 Sc3 BaaPt40175 Tb3BaaPt,01,

+8 +3 +2

+2 +2

+2 +2 +2 +5 +5 +4

+4, +6 +4

+4

+4

+4

+4 +2 +2, +4

-

- -

- -

- - - - -

tetragonal, PUrnbm, a = 0.6523, c = 0.5831 nm as above orthorhombic, Pmmm, a = 0.3841, b=0.3883, c=1.1617nrn

cubic, face-centred, F-cell, a = 0.8341 nm

monoclinic, CUc, a = 1.2518, b = 0.5828, c = 0.7362 nm monoclinic, Cam, a = 1.251 6, b = 0.5813, c = 0.7350 nm orthorhombic, Pnma, a = 1.31 91, b = 0.5680, c = 1.0301 nm rhombic, Pcmn, a = 1.0287, b = 0.5659, c= 1.3157nm as above

pseudocubic, perovskite, a=1.2316nm centrosymmetric, CUm a=1.2316nm

rhombic, Pcmm, a = 1.0287, b = 0.5655, c = 1.3157 nm hexagonal, a = 0.5803, c = 1 .a450 nm Abma, a = 0.541 6, b = 0.541 6, c = 1.2943 nm hexagonal, a = 1.0050-1.0078, c = 0.8320-0.8352 nm Prn3m, a = 0.83441 nm Pm3m, a = 0.83145 nm Pm3m, a = 0.83296 nm cubic, PmSm, a = 0.81531 nm cubic, PmSm, a = 0.8571 nrn

herein herein 32

32 20

herein herein herein herein herein herein

herein herein 2,27,28,29 29

30,31

31

31 32 33

34

35 36

37 38

39

40 40 40 41 41

is assumed, the oxidation state of osmium is 5+, and rhodium, iridium and palladium are all in their standard valence states. In addition, ruthenium, rhodium, and iridium form only

one compound with the Y-Ba-Cu-0 system, while the platinum and palladium systems are the most diverse. The ability to form perfect crystals (particularly iridium, platinum, osmium), their


YBaCusPd,Olo

YsBa5CusPd,0, YzBaCu20sOlo5 YBaCu,Oso YBaCulr,Ou

Y B&CUaPdrOm

YzBaCUPtOs

Nd2BaPdOs Y Ba2Cu2.SPd0.507

YBaCurPdrOlo5

semiconducting properties, ease of synthesis and stability in air and vacuum make these corn- pounds quite possibly suitable for engineering

Readers who wish to receive a copy of XRD data on Y,Ba,oCuRh,O,o, YBaCu,Pd,O,,,,, YBa,Cu,Pd,O,,, Y6Ba,Cu,Pd,0zo and Y,Ba6CuIr60~,,r established during these investigations should send their request to Dr. Yu. M. Shul‘ga, Institute of Chemical Physics, Chernogolovka, 142432, Moscow Region, Russia.

and chemical technology (as catalysts for oxidation and burn-off of waste gases, in fuel cells and for semiconducting techniques).

References 1 J. D. Bednorz and K. A. Muller, Z. Phys. E,

Conuhs. Mum, 1986,64,189 2 E. F. Maher, Plarinum Metals Rev., 1991,35, (l), 2

3 E. N. Izakovich, A. T. Mailybaev, G. D. Sokolmkaya, Yu. M. Shul‘ga, V. I. Rubtsov, Yu, M. Korolev, V. N. Spector and M. L. Khidekel, Phys. Status Solidi (a), 1991,124,525

4 B. R. James, “Homogeneous Hydrogenation”, Wdey-Intersci. Publ., New York, 1973

5 I. E. Graboi, A. P. Kaul and Yu. G. Metlin, “Itogi Nauki i Tekhniki. Ser. Khimiya Tverdogo Tela” (Russ.), 1988,6, 37

6 D. H. hhtthew, A. Bailey, R A. Vaile, G. J. Russell and K. N. Taylor, Nature, 1987,328,786

7 H. D. Tostarndt, M. Calf@, A. Freimuta and D. Wohllenben, Solid State Commun., 1989,69,911

8 M. Nunez Requeiro, P. Esquenazi, M. A. Izbizky, C. Duran, D. Castello, T. Luzuriaga and G. Nieva, PhyssiCa, 1988, C153,1016

9 S. R. Shenoy, Physka, 1988, B152,72 10 C. D. Wagner, W. H. Riggs, L. E. Davis, J. F.

Moulder and H. Mullernerg, eds., “Handbook of X-Ray Photoelecwn Spearuscopy”, Perkin-Elmer Corp., Minnesota, 1979, p. 190

11 J. H. Scofield, Livemore h h Rep, UCRL51326, 1973

12 N. Nuckel, J. Fink, B. Renkel, D. Ewert, C. Politis, P. J. W. Weijs and J. C. Fuggle, Z. Phys., 1987, B67, 1

13 H. Ihara, M. Hirabayashi, N. Terada, Y. Kimura, K Sensaky, A. Akimoto, K. Bushida, F. Kawashima and R Uzuha,M. J. AppZ. Phys., 1987,26, LA60

14 P. Steiner, V. Kinsinger, I. Sander, B. Siegwart, B. Hufher, C. Politis, R. Hoppe and H. P. Muller, Z. Phys., 1987,67,487

15 Yu. M. Shul’ga, V. I. Rubtsov, E. N. Izakovich and Yu. G. Borod’ko, S u r j a (Russ.), 1991,6, 121

16 V. I. Nefedov, “X-Ray Photoelecwn Spectroscopy of Chemical Compounds” (Russ.), Khimiya, Moscow, 1984, p. 284

17 M. N. Firsov, V. I. Nefedov and E. P. Domashevskaya, J. Snuct. Chem. (Russ.), 1979, 20,49

18 Y. Nishii, S. Moriya and S. Tokunaga, Phys. Len., A, 1987,126,55

19 T. J. Wagener, Y. Gao, I. M. Vitomirov, C. M. Aldao, J. J. Joyce, C. Capasso and J. H. Weaver, Phys. Rev. B, 1988,38,232

20 G. Ferrey, A. LeBail, Y. Laligant, M. Merkieu, B. Raveau, A. Suplice and R. Tournier, J. Solid State Chem., 1988,13,610

21 K. S. Kim, A. G. Goosmann and N. Winograd, Anal. Chem., 1974,46, 197

22 V. I. Nefedov, N. M. Spitsyn and Ya. V. Salyn, fiord. KhimGa (l?uss.), 1975,1,1618

23 G. J. Leigh and W. Bremser, J. Chem. SOC., D d m Trans., 1973, 1216

24 A. M. T. Bell, S u p e r d . Sci. Zchnol., 1990,3,55 25 A. V. Bulatov, T. P. Geidei, S. N. Usmtskii, I. Ya.

Turaev, M. L. Khidekel, Yu. M. Shul‘ga and N. M. Yaroshenko, Kinet. Kaml. (Russ.), 1988, 29, 238

26 K. S. Kim, N. Winograd and R. E. Davis,J. Am. Chem. SOC., 1971,93,6296

27 E. A. Genkina, 0. K. Melnikov, A. B. Bykov and B. A. Maksimov, fiidbgra$ya, 1989,34,1426

28 G. Calestani, C. Rizzoli and G. D. Andreorti, Solid State Commun., 1988,66,223

29 U. Geiser, L C. Porter, H. H. Wang, J. A. Allen and J. M. Williams,J. Solid Suue Chem., 1988,73,243

30 J. S. Swinnea and H. Steinfink, Acta Cryst., 1987, C43,2436

31 N. Toyota, I? Koorevaar, J. van der Berg, P. H. Kes, T. Shisido, Y. Saito, N. Kuroda, K. Ukei and J. Sasaki,J. Phys. C o h . Matter, 1989,1,3721

32 Y. Laligant, G. Ferrey, M. Hervieu and B. Raveau, Eur. J . Solid State Img. Chem., 1988,25,111

33 I? Guuzerh, F. Robert, J. Gouzerfi and H. Makram, J. Cryst. Growth, 1990, 102, 1059

34 M. Hiorth, Acta Chem. Scad., 1988,42A, 727 35 U. Amador, E. Mom, M. Alario-Franco, A. Vegas,

M. Martinez-Ripoli, J. Ibanez and J. B. Torrance, PhyssiCa C, 1989, C162,8731

36 I. Shishsido, T. Fukuda, N. Toyoto, K. Ukei and T. Sasaki, J. Cryst. Growth, 1987,85, 599

37 Z. Chen,Y. Qian,Y.wU,D. Sun,RLin,T Cheng, L. Niu, G. Zhou, Z. He, J. Xia, Y. Zao and Q. Zhang, J. Cryst. Growth, 1989,94, C277

38 H. K. Muller-Buschbaum and A. Teichert, J. Less- Common Met., 1989, 155,9

39 Y. Qian, Z. Chen, T. Chen, G. Pan, Q. Zhang, J. Xia, Y. Zhao, Z. He, G. Zhow, T. Cheng and L. Niu, M u m Res. Bull., 1988,23, 119

40 W. Gutau and H. Muller-Buschbaum, Z. Anorg. Ang. Chem., 1990,584,7

41 W. Gutau and H. Muller-Buschbaum, J. Less- Common Met., 1990,159,223


A Selective Review of Metal-Hydrogen Technology in the Former U.S.S.R. ADVANCED PAw;ADIUM APPLICATIONS FEATURED

Substantial mineral wealth and a long metallurgical tradition have made the states of the former Soviet Union highly developed in terms of advanced metals technologies. One particularly well developed technology concerns the interaction of metals with hydrogen. The First International Conference on Diffusive- Cooperative Phenomena in Metal-Hydrogen Isotope Systems, held at the Donetsk Polytechnic Institute, Donetsk, Ukraine from 15th to 19th September 1992, provided an opportunity to review some of the recent developments and the main themes in metal-hydride technology in the Confederation of Independent States (CIS). The conference included around 200 papers from all states of the CIS, with around forty concerned specifically with the platinum group metals.

Topics covered during the conference included fundamental research concerning the nature of metal-hydrogen systems, their physical and electrical properties, and phase transformations. The detrimental effects of hydrogen on construction materials such as steel and materials associated with nuclear engineering were considered in a series of paper contributions. Some thirty papers on cold fusion testified to the per- sistent and perplexing nature of this phenomena. Reported applications of metal-hydrogen technology included: hydrogen processing of materials, hydrogen generation and storage and hydrogen purification technology based on palladium alloy membranes.

Fundamental Physical Phenomena in Metal-Hydrogen Systems

Many of the contriiutions in this category were concerned with the changes brought about in the physical and mechanical properties of metals which can be brought about by successive hydrogenation-dehydrogenation cycles. V. A. Goltsov

of the Donetsk Polytechnic Institute has descn’bed this type of phenomenon using the Russian term “hydrogen phase naklep” (1).

Hydrogen Phase Naklep Much modern physical metallurgy is based on

the polymorphism of metals. It is the porymorphic character of steel which allows the regulation of mechanical and physical properties via heat treatments. However, a large number of metals are not polymorphic and therefore only plastic deformation and subsequent re-crystallisation can be used to modify and control their properties.

The basic premise of hydrogen phase naklep is that a metal is charged with hydrogen elearo- chemically or under gas pressure to form the hydride phase. The metal is then cycled through several hydrogenation-dehydrogenation cycles during which the material undergoes repeated volume expansion and contraction. This results in the development of internal stresses and defect generation. Under controlled conditions the de- gassed material may be transformed into a new, state, characterised by high strength and with modified physical and mechanical properties. The conditions for hydrogen phase naklep will vary according to the metal. Strong hydride forming metals such as palladium, niobium, titanium and zirconium may only require fractions of a bar of hydrogen in order to be processed by hydrogen phase naklep. Metals which absorb hydrogen less readily will require higher hydrogen pressures in order to achieve similar results. In principle at least, hydrogen phase naklep should be applicable to all metallic elements.

The fact that a very large number of metals will reversibly absorb hydrogen offers the opportunity of using hydrogen phase naklep to modify their properties without recourse to working. An example of a material which can be readily processed by hydrogen phase naklep is palladium.

Platinum Metals Rev., 1993,31, (Z), 97-101 97

Palladium is not polymorphic but occludes hydrogen easily at room temperature. Hydrogen phase naklep applied to palladium (35 to 40 hydrogenation dehydrogenation cycles) allows the ulti- mate tensile strength and yield limit to be increased by 1 to 3 times that of annealed palladium, which is equivalent to 80 per cent plastic deformation. A similar hydrogen treatment increases the microhardness of palladium by a factor of 2.5 compared to the annealed metal. Therefore, when applied to palladium, hydrogen phase naklep results in an increased strength, high plasticity state such that the ability of the material to withstand large deforming loads is significantly enhanced.

The effect of hydride transformations in palladium on electrical resistance was reported by A. P. Kusin, Donetsk Polytechnic Institute. An interesting conclusion of this work was that the effects of multiple saturation-degassing cycles do not simply accumulate in palladium. In fact after several cycles a very stable structure with an increased electrical resistance is formed.

Results detailing the kinetics and morphology of the a-B phase transformation in a series of palladium samples under a hydrogen pressure of 0.1 to 0.2 MPa and temperatures in the range of 20 to 3OOOC was presented by Yu. A. Artemenko, Donetsk Polytechnic Institute. One of the techniques utilised in this work involved the direct optical observation of palladium during the a-i3 phase transformation. Under isother- malmaric) conditions the phase transformation proceeds through “massive” precipitation. This is followed by a period of reduced growth before an explosion of “needles” heralds a further period of “massive” growth. This cyclic precipitate growth is a function of the diffusive flow of hydrogen towards the growing hydride phase. Migration of hydrogen towards the growing hydride occurs due to the stress field distribution produced by the volume differential between the hydride and solid solution phase.

The effect of hydrogen treatments on the physical and mechanical properties of several palladium-molybdenum alloys was reported by F. Bersenm and colleagues at the Ural Department of the Russian Academy of Sciences,

Ekaterinburg, Russia. The hydride phase was only detected in alloys with less than 6 atomic per cent molybdenum. Alloys containing larger amounts of molybdenum formed only dilute solid solutions with hydrogen. Those containing up to 10 atomic per cent molybdenum were strengthened during the initial stages of hydrogen charging, with the largest increase in strength occurring in alloys in which hydride formation took place. As the strength of the palladium- molybdenum alloys increased, alloys in which no hydride phase was formed became more plastic while hydride forming compositions became severely embrittled.

Hydrogen Processing of Metals Observations of various metal-hydrogen inter-

actions show that large changes can be wrought in the structures of metals by their reaction with hydrogen. In addition to the modified structures produced by hydrogen phase naklep, hydrogen has been shown to be capable of promoting and suppressing order-disorder phenomena in metals, and causing phase separation in some alloys (2). The accompanying changes in physical and mechanical properties resulting from the interaction of metals with hydrogen illustrates the potential for hydrogen as a useful tool for processing titanium and aluminium-silicon, for example.

Hydrogen Storage and Generation Interesting technology for the storage and pro-

duction of hydrogen was presented by R. G. Sarmunina of the Chemical and Metallurgical Institute, Academy of Science, Kazakhstan. Sarmurzina proposed a two-stage process in which multi-component alloys based on aluminium are first used to release hydrogen fiom water, with the residue from the reaction being later used as a dehydrogenation catalyst for the production of fkther hydrogen from hydrocarbon feedstocks. The result is a near wasteless process for hydrogen generation fiom water and fiom hydrocarbons, such as cyclohexane.

The process begins with an alloy of aluminium with gallium, indium and platinum. This material reacts spontaneously with water to evolve

Platinum Metals Rev., 1993, 37, ( 2 ) 98

hydrogen and produce aluminium hydroxide phases. Sarmunina presented a wealth of data detailing the hydrogen evolution process. The by-product of the hydrogen evolution reaction of the aluminium alloy with water is a mixed pseudo-boehmite and beyerite material impregnated with gallium, indium and platinum. The relative composition of the hydroxide phases appears to depend on the platinum content of the initial alloy. After calcining the mixed product, a platinum-gallium-indium on alumina catalyst is formed which is highly active for dehydrogenation of organics. Catalysts with 0.5 to 1 weight per cent platinum yielded 96 to 98 per cent benzene from cyclohexane, the dehydrogenation beginning at around 250°C. The reaction is entirely selective and at 35OOC conversion reaches 99.9 per cent. The high activity of the catalyst prepared in this way, from the reaction of a bulk alloy with water, was due to highly dispersed platinum promoted by gallium and indium on the developed alumina surface.

Hydrogen Purification by Diffusion through Palladium Alloy Membranes

Another technology which has reached an advanced state of development in the CIS is hydrogen purification using palladium alloy membranes. Although commercial examples of palladium alloy membranes exist outside the CIS these are generally limited to very small scale units passing between 1 and 50 cubic metres of hydrogen per hour. A recent publication in this journal highlighted a diffusion membrane plant developed by The State Nitrogen Industry (Moscow), capable of a hydrogen throughput of around 2000 cubic metres per hour (3). This represents a rare example of a medium-large scale application of palladium alloy membranes.

One of the striking aspects of palladium membrane development in the CIS is the attention which has been paid to alloy development. Whereas most membrane units outside the CIS use the standard palladium-23 per cent silver alloy, the range of materials used in the CIS is more diverse, centred around the so called B- series alloys (4). The %alloys are a range of multicomponent alloys often containing 4 to 6 ele-

ments, each composition designed for a particular set of operational requirements. Examples of the B-series of alloys include: B 1 (Pd-AgAu-Pt-

B6(Pd-Au-Fe). Alloys B2 and B4 have a high hydrogen capacity and hence a high hydrogen permeability, alloys B3, B9 and B11 are designed for high operating temperatures, while alloys B1 , B5, B9 and B11 are capable of withstanding large pressure drops. Alloys B1, B4, B5, B9 and B11 are relatively resistant to cycling, alloys B1, B4 and B5 have increased resistance to poisoning and alloys B1 , B2 and B5 show the largest isotope effects, useful for separating protium, deuterium and tritium. The alloys B2 and B3 are both capable of being strengthened in use, by hydrogen phase naklep (5).

The state of development of membrane technology in the CIS was illustrated at the Donetsk conference by more than a dozen papers.

The technological problems associated with the use of palladium alloy diffusion membranes for large scale applications were examined by V. M. Makarov, Ural Department of the Russian Academy of Sciences, Ekaterinburg, Russia. A crucial aspect of this technology is the selection of the membrane alloy. Makarov found complex alloys of palladium with other platinum group metals effective both in terms of high hydrogen throughput and high strength and durability.

The influence of local inhomogeneities, impurity elements and defects which alter the performance and durability of membrane systems was discussed by V. G. Sorokin of the St. Petersburg Technical University, Russia. In particular the segregation, accumulation and re-arrangement of small amounts of impurity elements such as potassium, calcium, magnesium, silicon, sulphur, titanium, iron and copper to the grain bound- aries was seen as contributing to the early failure of membranes.

Shortcomings of the widely used palladium-20 to 25 per cent silver diffusion membrane alloy, in terms of its low strength and tendency to coarsen its structure during long term operation was discussed by N. I. Timofeev and co-workers at the Ekaterinburg Plant for the Treatment of Non- Ferrous Metals, Russia. Multi-component

Ru-Al), B2(F'd-Ag-In-Y) , B4(Pd-Ag-Y-Yb) and


alloys based on palladium-silver and palladium- platinum alloys were reported to show considerable improvements in their mechanical characteristics compared with the simple binary systems.

The influence of hydrogen dilation on the deformation and early cyclic failure of palladium alloy membrane elements has been examined by A. I. Berezin and colleagues at the State Technical University of Chelyabinsk, Russia. In particular, non-homogeneous hydrogen concentrations led to differential expansion within membrane elements and the resultant high stress states caused early membrane failure.

Three stages of production of tubular and flat foil membrane elements, namely alloy preparation and working; heat treatment; and welding were described by V. A. Kon’kova of the Ural Plant of Chemical Engineering, Ekaterinburg, Russia. Membrane elements manufactured by the methods outlined are currenty being operated on an industrial scale. A large amount of data for these membranes under industrial conditions, were presented.

Eugene P. Chistov and co-workers of the State Scientific and Industrial Enterprise “Quantum”, Moscow, presented a compact hydrogen purification membrane based on the B1 alloy. The device was of sheet construction with a number of individual “flag” membrane elements stacked together to give a hydrogen flow of up to 30 cubic metres per hour, at 50OOC and 10 bar pressure.

A report of an examination of the behaviour of two membrane alloys, palladium-6 per cent ruthenium and B1, in a coke gas mixture was presented by V A. Kurakin, Lugansk E n g i n e Institute, Ukraine, and colleagues from the Ekaterinburg Plant in the Treatment of Non- Ferrous Metals, Russia. The work was aimed at studying the passivation processes which occur when membranes are exposed to impure gas streams.

Both alloy membranes suffered a decrease in permeation performance after 16 hours exposure to the coke gas at 0.1 MPa pressure and a temperature of 550°C. A higher surface activity was noted for the palladium-6 per cent ruthenium alloy, confirming the beneficial effect of ruthenium on the catalytic activity of palladium.

A second presentation on the separation of pure hydrogen from coke gas was made by A. P. Kusin, Donetsk Polytechnic Institute. The report stressed that while many of the problems of construction and use of palladium alloy membranes have been solved, the application of this technology to impure gas streams is not yet well studied. Within the CIS groups were working on this problem and specifically looking at “off-gases” such as coke gas. An important conclusion of this early work was that although impure gas streams slow down the flow of hydrogen, these membranes do remain permeable to hydrogen.

Two reports focused on the effects of carbon films formed on palladium alloy diffusion apparatus as a result of hydrogen separation from hydrocarbon containing gas streams (I. E. Gabis et al, Physics Research Institute, St. Petersburg University, Russia). Experiments were carried out on films produced by the decomposition of natural gas on the B 1 alloy. Graphite-like coatings, which formed under the conditions in which the purifiers operated, tended to slow down the permeation process. A model was developed to help optimise the operation of palladium alloy elements under such conditions.

Catalyst Membrane Technology The use of palladium alloy membranes in cat-

alytic devices is another technology developed within the CIS which has been the focus of international attention. An impressive body of literature exists largely due to V. M. Gryanov and co-workers, A. V. Topchiev Institute of Petro- chemical Synthesis, Moscow (6). The metals- orientated nature of the Donetsk meeting probably deterred many catalyst scientists from attending. However, the possible use of palladium metal membranes as catalytic devices was reported by B. Yu. Nogerbekov et al (Institute of Organic Catalysis and Electrochemistry, Alma- Ata, Kazakhstan). The absorption of hydrogen into a palladium membrane was achieved elec- trolytically fkom a 0.1 M sulphuric acid solution. The atomic hydrogen thus produced was used in the hydrogenation of various classes of organic compounds including acetylene spirits, benzoquinone and also aromatic nitrogen


compounds, with the catalytic activity dependent on the polarising current density.

Conclusion This conference provided an excellent oppor-

tunity for the international community to exam- ine the extent of the development of metal-hydrogen technology within the CIS. Hydrogen phase naklep, diffusion membrane and membrane catalysis technology based on palladium are examples where work carried out in the CIS constitutes the “state of the art”. These areas therefore appear likely to continue to attract growing international attention in the future.

Acknowledgement Grateful thanks are due to Professor V. A. Goltsov

and Valentina Garkusheva for the preparation and translation of the conference abstracts.

References 1 V. A. Goltsov, Manx Sci. Ens, 1981,49, 109 2 T. B. Flanagan and Y. Sakamoto, Platinum Metals

Rev., 1993,37, (l), 26 3 V. Z. Mordkovich, Yu. K. Baichtock and M. H.

Sosna, Platinum Met& Rev., 1992,36, (2), 90 4 Russian Patent 463,729; 1975 5 N. I. Timofeev, F. N. Berseneva andV. M. Makarov,

“Hydrogen Energy Progress M”, Proceedings of the 9th World Hydrogen Energy Conference, Paris, France, 22nd to 25th June 1992,1,207-209

6 V. M. Gryazanov, Platinum Met& Rev., 1992,36,

M.LD.

(21~70

Reduction of Nitrogen Oxides by Hydrocarbons PERFORMANCE OF PLATINUM METALS CATALYSTS INVESTIGATED

The removal of nitrogen oxides present in the gases emitted from sources such as electric power generation boilers, stationary internal combustion engines and gas turbine engines- all of which are likely to use excess oxygen to achieve maximum fuel efficiency-can be achieved by a selective reduction process using ammonia as the reducing agent, the reaction being carried out over a base metal oxide catalyst. It had been considered that hydrocarbons were ineffective for th is reaction but recent work has indicated that with suitable catalysts it may be possible to use them in a process which removes nitrogen oxides kom the exhaust gases of both diesel and lean-burn gasoline-fuelled engines. For practical application, high activity under high space velocity and also high selectivity would be required.

The activity and durability of a variety of catalysts have been investigated, but to-date there has been only little interest in using the platinum metals as catalysts for this purpose. Now, however, a team at the National Institute for Resources and Environment, Tsukuba, Japan, have investigated the performance of platinum, palladium, rhodium, iridium and ruthenium supported on y-alumina as catalysts for this application (A. Obuchi, A. Ohi, M. Nakamura, A. Ogata, K. Mizuno and H. Ohuchi, “Performance of Platinum-Group Metal Catalysts for the Selective Reduction of Nitrogen Oxides by Hydrocarbons”, Appl. Cutal. B: Environ., 1993, 2, (l), 71-80).

The addition of some hydrocarbons to the exhaust is necessary to compensate for the greater amount of nitrogen oxides generally emitted from combustors operating under net- oxidising conditions, and the properties of

propene favour its use as the reducing agent. With both model mixtures and real diesel exhaust gases it was found that platinum- rhodidy-alumina displayed high activity for nitrogen oxides conversion, at 200 to 35OOC. These catalysts are similar to the three-way catalysts used for controlling emissions from gasoline fuelled engines. It is concluded that platinum metals catalysts will find practical usage for this purpose, especially if their selectivity to nitrogen is improved.

Nanoscale Platinum Technology As microelectronic device and computer com-

ponents are reduced to sub-micron size there is a need for metal features of nanometre thickness. At the Naval Research Laboratory, Washington, a method has been developed for fabricating platinum patterns of varied geometry which may be as little as 20 nm thick and with heights of up to 700 nm. These are produced by thermal decomposition of a platinum precursor molecule, tetrakis-(trifluorophos- phine)-platinum, onto the surface of a contoured substrate. A detailed description of the fabrication process, and an analysis of the properties and morphology of the platinum film structures have recently been published @. S. Y. Hsu, N. H. Turner, K. W. Pierson and V. A. Shamamian,

The substrate is amorphous silicon, fabricated by lithographic techniques suitable for large scale processing, and this permits a very thin polycrystalline platinum film to be deposited, which in turn makes possible the production of ultranarrow patterns with 20 nm liewidths. It is suggested that further reduction in linewidth is possible by improving various parameters.

3 V~C. Sci. TechnoL B, 1992,10, (5), 2251-2258).


Early Studies of Platinum in Spain THE CONTRIBUTION MADE BY JOSEPH LOUIS PROUST

By R. Moreno Garcia Unidad Docente de Quimica, E.T.S.I. de Montes, Universidad PolitCcnica de Madrid, Spain

A critical study is presented here of the contribution made by Joseph Louis Proust, Professor of Chemistry and Metallurgy at the Royal Artillery School in Segovia, to the early investigation ofplatinum. His researches were carried out in Spain, muidy at the Segovian House of Chemistry during the latter ymrs of the eighemth century, and at theplatinum laboratory in Madrid in the earlyyears of the nine- teenth century. These investigations resulted in three papers about the metal; one of them is almost unknown, but it gives aprocedure which he had established for the possible purijication of platinum. In the other two, Proust incorrectly interpreted the results of his experimental work, but he showed a systematic approach to his scientifi investigations and paid great attention to detail, being the only investigator of platinum in Spain at that time to do so.

Following the formal announcement of the 1754 the Englishman William Lewis, in 1757 discovery of platinum by A. Ulloa in 1748 (l), the German chemist Andreas Segismund there was great interest throughout Europe in Marggraf, and the following year the Frenchmen the investigation of this substance. In 1752 the Pierre Joseph Macquer and Antoine Barn&, pm- Swedish scientist Henrik Theophil Scheffer, in vided the first important chernicaVmetallurgica1

Joseph Louie Prouet 17% - 1826

Born in Angers, France, Proust spent three years at Vergara in the Seminario Patri6tico. In 1788, he wm appointed h f m r of Chemistry and Metdhqy at the Royal Artillery School at !%?govia, by the King of Spain. In the laboratory in Segovia, which was reputed to be equipped with platinum apparatus, and later on in Madrid he established a working procedure for the purification of platinum. His laboratory in Madrid was destroyed in 1808 during the eiege of Madrid by Napoleonic forcea

Platinum Metals Rev., 1993,37, (2), 102-107 102

contributions to the systematic study of platinum, this new metal from South America (2).

Spain could not stand aside from the investigation of this “Exclusive Spanish Metal”, as it was referred to by Herrgen (3). However, the scientific facilities available in Spain at that time, especially in the field of chemistry, were hardly adequate for the adulteration of gold with platinum to be investigated in an effective way. This hudulent use of platinum was practised habit- ually in Spanish America (4), with unfortunate economic consequences for the Spanish Crown. None the less the botanists Cristobal Vklez and Pehr Lijfling, and the Irish naturalist William Bowles (1705-1780) investigated platinum in the early 1 7 5 0 ~ ~ although their investigations were not necessarily directly related to the problem of gold adulteration. Indeed, we think that they were probably carried out solely for scientific interest (5).

During the latter part of the eighteenth century, however, investigators in Spain achieved some success. In 1786, a young Frenchman named Pierre Francois Chavaneau (the Spanish spelling is Chabano) and his Spanish silversmith Francisco Alonso became the first people in met- ropolitan Spain to achieve purification of native platinum, so facilitating its industrial application and enabling smiths to manufacture platinum articles of fine quality. This epoch was named by Don Juan Fag& y Virgili as the “Platinum Age in Spain” (6), a most fortunate expression that has been revived in the definitive work on the history of platinum (7).

The conm%ution by Louis Proust was made at the end of the “Platinum Age in Spain”, that is in the last years of the 18th century and the early years of the 19th century. Three publications about platinum resulted: the first of these was published in 1795 in volume two of the A& del Real LaboratmM de Quimica de Segovia (€9, the second appeared in the A& a2 Historia Nanrml de Muddin 1799 (9) and, finally, a letter sent to Nicholas Louis Vauquelin (1763-1829) on 6th November 1803 was published in Paris in the Annales de Chimie the following year (1 0).

In the prologue to the first of these three communications, Proust had noted “To the Memories

that compound this notebook we could add a lot more about the animal analysis, about the platinum”. Clearly by that time Proust must have been knowledgeable about platinum, most likely because he had carried out investigations in Segovia during the early 1790s. Later, of course, he would have performed experiments in Madrid at the Turco Street laboratory where he was in charge during 1799, following the departure of Chavaneau in 1797 (1 1). Some of Proust’s observations were probably contained in the letter that he sent to Vauquelin, as certain manuscripts and documents relating to Proust are known to exist in the Indian Archive of Seville.

For the present, we shall ignore whether Proust was ordered to investigate platinum, or if the research was done by “motu proprio” (his own wish). However, on 27th April 1786 his great protector, the Count of Lacy requested the Marquis of Sonora to make some platinum available to Louis Proust, who the King of Spain had just appointed Professor of Chemistry and Metallurgy at the Royal Artillery School at Segovia.This was to enable Proust to increase his knowledge of platinum which he could then communicate to his students, as well as to assess the advantages that could be gained from the use of this metal (12).

The First of the Publications The brief note that he published in the “Anales

de Quimica de Segovia” can be translated as follows:

“Platinum. All the ones that I have examined contain copper. If a solution of platinum is precipitated by a plate of pure iron, and the nitric acid is applied to the precipitated platinum, the copper and the oxide of iron are taken out; and pouring hepatic water in this acid copper is precipitated”.

Thus he gives a practical and efficient method of eliminating the copper contained in the platinum by the use of “hepatic water”, an aqueous solution of hydrogen sulphide.He describes the procedure succinctly, but he does not give it as a method for refining platinum. The reported procedure, however, would have resulted in a substantial purification of the native platinum and it is possible that Proust would have used this

Plarinum Metak Rev., 1993,31, (2) 103

Native Platinum Ore

Chocd

Element

Pinto river

Pt Pd Rh Ir 0 s Ru Fe cu Mn 0s-lr

86.1 6 0.35 2.16 1.09 0.97 0.00 8.03 0.40 0.1 0 1.91

method to purify the inferior platinum sent to him from Chavaneau’s laboratory in Madrid. This view is supported by a communication h m the Segovia laboratory dated 1791, in which he asks for unpurified platinum to be sent to him so that he could use it for fabricating crucibles (1 3). This suggests that he had at his disposal a more adequate refining procedure than the one used by Chavaneau.

The procedure he describes consists of treating the solution of platinum in aqua regia by the cementation of the metals dissolved in it with an iron plate; the metallic powder obtained in this reduction was later treated with nitric acid, and the copper in this solution was detected with hepatic water.

The general composition of the native platinum from the Choco and the Pinto River, as given by Svanberg (14), is shown in the Table.

Treatment in aqua regia will dissolve all the platinum and palladium, as well as iron, copper and manganese; but because the rest of the platinum group metals are practically insoluble in aqua regia a very rehctory powder remains. By repeated attacks with this solvent, and with considerable difliculty, a partial dissolution can be achieved. Treatment of the platinum solution in aqua regia with an iron plate, as indicated by Proust, would give a precipitate in powder form, made up of a mixture of platinum, palladium and copper. The iron and the manganese would

84.34 1.66 3.13 2.58 0.19 0.00 7.52

traces 0.31 1.56

not be reduced by the metallic iron but would stay in the solution. Treatment of the powder mixture with nitric acid would dissolve the copper and the palladium as nitrates, while leaving the platinum powder in a practically pure form. Thus the procedure offered a worthwhile route for the elimination of iron, which was abundant in the platina ore. The elimination of iron con- stituted a major advance in the production of

A platinum crucible mneerved in the Artillery School of Segovia, the wmtruction and use of which is attributed to Louis Proust, although no documentary evidence for this exists. The height of the crucible is approximately &m


Composition, per cent

NATIVE PLATINUM ORE (platinum, palladium, rhodium, iridium, osmium, copper, manganese)

Treatment with aqua regia

3 Soluble bct ion Insoluble refractory powder

Pt, Pd, Fe, Cu, Mn, (Ir+Rh) in form of chlorides

secondary platinum group metals

Reduction or cementation with metallic iron

Soluble fraction Fe and Mn chlorides

Metallic powder residue Pt, Pd, Cu, (Ir+Rh)

Treatment with nimc acid

Soluble hction Pd and Cu nitrates

Residue pure Pt, (Ir+Rh)

The Procedure Used by Proust for the Purification of Platinum

fitinurn Metals Rev., 1993,3?, (2) 105

platinum metal; Chavaneau’s method of precipitation with potassium chloride or ammonia, as well as the techniques used by other investigators, resulted in the retention of a certain amount of iron which later decreased the mal- leability of the platinum. The procedure that we assume Proust used for the purification of platinum is shown here schematically.

This procedure has been, and indeed still is, very important in noble metals refining where the cementation of the platinum group metals by zinc or iron powders is employed at different stages in the separation.

The Second Publication The second of Proust’s publications about plat-

inum was a lengthy article divided into fifteen chapters which appeared in the Anales a2 Historia Natural in 1799. The more important aspects of this article, which is perhaps the least analysed of Proust’s work, are now considered:

In Chapter III he writes about the presence of gold in the platinum, evaluating the former at about 10 per cent and noting that he had already communicated this figure to the Ministry. This tends to confirm the inadequacy of the amalga- mation method of separation, as carried out in Spanish America during the eighteenth century and which continued until the end of the colonial period.

In Chapter IV Proust makes one of his more important mistakes when he assumes that the platinum occurs as a sulphide and therefore is bound to sulphur. He makes this major error because of his incorrect interpretation of the platinum calcination experiments, and in doing so he lost an opportunity to identify a new element.

By means of a blowtorch he heated the platinum on a coal support, reporting that “it exhales a penetrating steam of sulphur accompanied by smoke” and that when he made the experiment in a closed crucible this did not happen, but as the crucible was uncovered “you can detect this smell stronger”. Later on, he continues “I have not been able to know the character of this steam for a long time, but at the end of these experiments it would seem that what I have found is nothing other than concentrated sulphuric acid”.

When he obtained this penetrating steam of unknown character, Proust probably associated it with sulphur, but in fact the native platinum ore does not contain sulphur, neither does it appear to be accompanied by any sulphur-containing minerals. In all probability, therefore, the so- called “steam” was osmium tetroxide. Thus, we might say that Proust let an opportunity to discover osmium “evaporate into thin air”.

Another error occurs in Chapters VI and W, which relate to the insoluble residue of the platinum solution in aqua regia. He observes that the residue can vary from 1.5 to 3.5 per cent depending on the type of sample and, incomprehensibly, he believes it to be graphite. This is an inexplic- able association because in the text he reports that “in the course of the platinum dissolution it seems to be reduced to a black powder, not less heavier than the platinum”. If it was the same density as platinum, it is difficult to understand why he associated it with graphite, the density of which at 2.25 g/cm3 is less than one-ninth that of platinum. This error deprived him of a chance to discover the existence of another new metal, namely iridium. As with osmium, Proust let the opportunity “slip through his fingers”. He continued with this error until at least 1803 when in his letter to Vauquelin he again alludes to the insoluble residue as graphite; in fact it was Vauquelin who recorded in a footnote that the material which Proust referred to as graphite was a new metal.

In Chapter M and later, Proust describes the dissolution of platina in aqua regia and records that the platinum dissolutions in this solvent, when taken to total dryness, are only partially insoluble and that the portion which does not dissolve is a little known acid, “muriato” (chloride). This was probably caused by the formation of insoluble rhodium trichloride, but once again Proust did not consider the possibility of other metals being present in the native platinum, and therefore he did not investigate the fact that one portion of the precipitate was soluble while the other was insoluble. He observed that solutions of black platina were redder than those of white platina, but did not attempt to explain this. In fact, the black platina contains a


greater amount of palladium and rhodium; when dissolved, these metals give a strong red coloration.

Finally, he observed that the precipitation of insoluble potassium chloroplatinate in the platinum solutions in aqua regia, was due to “salt- petre” (potassium nitrate), which exists as a con- taminant in commercial nitric acid and was present in the collar of the retorts.

Proust did not refer to the possibility of using chloroplatinic acid as a selective reagent to distinguish bennreen sodium and potassium salts, as only the latter precipitate. However, the author of the preceding article in the 1799 issue ofA& de Hist6ria Nanrml(l5) acknowledged that it was Proust who proposed that the reagent of the platinum dissolutions could be used to distinguish between the sodium and the potassium salts.

The Letter to Vauquelin In the third of his publications about platinum,

in which he continued to refer to the insoluble residue as graphite, Proust made two important proposals:

First, that a mixture of nitric acid and marine salt could be used instead of aqua regia to dissolve platinum, giving a platinum chloride “barrillk” (sodium), and he commented that its crystallisation was very easy and useful for the separation of iron chloride. Although not the first time that this mixture had been proposed as a solvent

for platinum, the comment was very pertinent as the sodium platinum group metal salts formed would be easily crystallised and very soluble. In these circumstances, the rhodium forms a soluble sodium chlororhodite, and he would not find the insoluble fi-action which appeared when he took the platinum dissolution in aqua regia to dryness.

His second proposal for the precipitation of platinum concerned the use of soluble sulphides instead of ammonium chloride

“as the black precipitates that are formed with the platinum lose the sulphur very easily and give a pure platinum powder that it can be agglutinated and forged, as with the ammonium salt”.

Again Vauquelin made a very pertinent comment: that the procedure would not be appropriate because it did not take account of the new metal, by which he meant palladium; even though Proust knew of the recent publication which reported the existence of palladium, apparently he had not considered the possibility of separating the two metals.

Acknowledgements This paper is based, in part, upon a presentation

made to the International Congress on Louis Proust, held in 1992 to commemorate the bicentenary of the inauguration of the Segovian House of Chemistry. My thanks are due to Professor R. Ferdndez de Caleya and L. Fernandez Pacios who read this manuscript and made useful suggestions.

References 1 A. Ulloa and J. Juan, “Relacih Hist6rica del Viaje

a la h & c a Meridional”, Madrid, 1748, A. Marin,

2 See for example D. McDonald, “A History of Platinum”, Johnson Matthey, London, 1962; D. McDonald and L B. Hunt, “A History of Platinum and its Allied Metals”, Johnson Matthey, London, 1982

3 E. Maf€ei, “Centenario de la Escuela de Minas de Espaiia, 1777-1877”, ETSI de Minas, Madrid, 1977, p.14

4 A. Galan and R. Moreno, Pkatinum Metals Rev., 1992,36, (l), 40

5 A report of the investigations undertaken by the three named scientists has been prepared for publication elsewhere

6 J. Fages Virgili, “Los Quimicos de Vergara y sus Obras”, 1909, maiden speech at Real Academia & Ciencias Exam, F&m y Naturales, p.59

2 3 0 , p.606

7 D. McDonald and L. B. Hunt, “A History of Platinum and its Allied Metals”, Johnson Matthey, London, 1982, p.93

8 L. Proust, Anal. RealLab. @im. a2 Segovia, 1795, II, 114

9 L. Proust, Anal Hktdria Natural, 1799,1,51 10 L. Proust, A n d . G% Chim., 1804,49, 177 11 Archivo de Indias, Leg.835,1797, pp.323-362 12 Ibid., pp.141-186, doc.5j 13 Quoted by L. Silvan, Boletin Real SOC. Basmgada

de Amigos OW Paris, 1969, S . Sebastian, Aiio XXV, 1 er cuaderno, p. 183

14 F. Stohmann and B. Kerl, “Gran Enciclopedia de Quimica Indusmal”, Barcelona, 1930, Francisco Seix, Tom0 XI, p.457

15 D. Garcia Fernhdez, A d Hk& Natural, 1799, 1, pp.46-51


ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES

The Transitions (5d”+5d76s)-5d’6p of Pt III A. N. RYABTSEV, J.-I;. WYART, Y. N . JOSHI, A. J. J. RAASSEN and P. H. M. UYLINGS, PhyS. scr., 1993, 47, 45-58 The sliding spark and triggered spark spectra of Pt have been observed in the range 559-2020 A. More than 800 lines have been classified as transitions between 40 levels of 5da+ 5d76s and 93 levels of 5d76p in doubly ionised Pt, with the support of accurate predictions using energy parameter regularities in the isoelecwnic sequence Ir III-Bi VIII, and by transition probability calculations which include explicitly the configuration mixing in the (5d + 6s)’ and 5d76p + 5d ‘ 6 ~ 6 ~ .

The Magneto-Optical Kerr Effect of Multilayers FeRt and Copt s. ZHOU, H. ZHAI, J. SONG and H. ZHANG, p Appl. Phys.,

The magneto-optical polar Kerr rotation spectra of multilayers FePt and CoPt were calculated based on two assumptions; the spin polarisation of the Pt layer was assumed to be negligible, and the Pt layer was assumed to be polarised and to contribute directly to Kerr rotation in the multilayers. The calculated results for Fe/Pt and C o p t multilayers dco(pc)/dR = 1 showed the magnetooptical Kerr rotation at 300-800 nm increased with increasing modulation wavelength.

1993,73, (2), 986-988

Atomic In-Plane Disorder in CoRt Superlattices x. YAN, T. EGAMI, E. E. MARINERO, R F. c. FARROW and c.

Studies of 4 1 1 > and Cool> oriented Co(3A))Ipt(l8A) superlattices grown by molecular beam epitaxy via X-ray diffraction were made using synchrotron radiation. For the < 1 1 1 > oriented sample, the broaden- ing was characterised by a Lorenuian peak shape with a positional correlation length of the order of 50 A.

H. LEE, A@I. Phys. A, 1992, A55, (6) , 545-548

Thermodynamic Investigation of the Pt-Pb Binary Alloys A. AMZIL and R. CASTANET, Ber. Bunsenges. Phys.

The enthalpy of formation of the Pt-Pb alloys was measured at 923-1316 K with respect to composition by direct reaction calorimetry with the help of high temperature Calvet-type calorimeters. The thermodynamic behaviour of the melts was characterised by moderate negative deviations to ideality, suggest- ing some chemical short-range order at 923 K. The associates are very sensitive to temperature since the excess heat capacity is positive with a maximum of- 10.2 J/K.mol near mole fkaction x, = 0.71.

Ch., 1992,96, (12), 1872-1876

Effect of Temperature Gradient on Concentration Profile of Hydrogen in a Palladium Lattice w. M. LEE and H. s. UHM,J Appl. phys., 1993,73, (3),

The imposition of a linear temperature increase upon a one-dimensional Pd hydride rod caused a significant redistribution in H concentration. The induced concentration gradient was opposite to that of the imposed temperature gradient due to the positive heat of transport. A Pd hydride rod, in which the Q and l3 phase co-existed prior to imposition of the thermal gradient will have a discontinuous H distribution.

Changes in Film Structure and Increase in Coercivity for CoRd Multilayered Films with Atmospheric Annealing H. YAMANE, Y. MAENO and M. KOBAYASHI, J. Appl. Phys., 1993, 73, ( l) , 334338 Studies of changes in the film structure of Co/Pd multilayered sputtered films before and after atmospheric annealing showed that coercivity greatly increased to 2 kOe with atmospheric annealing at 300°C. However, this increase was only observed in atmospheric annealing but not in vacuum-annealing.

The Pd Polarization at the Pd/Fe Interface

and H. DREYSSE,~ Map. &Map. Marer., 1993,118,

Studies of the electronic and magnetic properties for a film of n adlayers of Pd grown on semi-infinite Fe(OOl), for Fe,/Pd./Fe, sandwiches and (Fe,/Pd.), superlattices were performed by a mean-field para- meterised tight-binding method. Antiparallel coup1 ing of the Pd layers was observed in PdJFe(001). Ferromagnetic polarisation of the Pd. layers were obtained up to n = 3. For n = 4, ferromagnetic polarisation of the nearest neighbour Pd overlayer was obtained, but negative polarisation was observed for the three other planes.

Strain Gradient-Induced Diffusion of Hydrogen in Palladium and Nickel Membranes Y. SAKAMOTO, H. TANAKA, F. A. LEWIS and x. Q. TONG, In?. J. Hydrogen Energy, 1993, 17, (12), 965-970 Studies of the “uphill” diffusion of H during permeation through flat sheets of Pd and Ni were made by an electrochemical permeation method at 303 K. For both annealed and “as cold rolled” Pd samples, uphill diffusion effects on H absorption and desorption were observed over a range of initial H contents from - H:Pd = 0.01, which is near or slightly less than the a- composition, up to H:Pd = 0.254.3.

1011-1017

H. NAlT-IAZIZ, S. BOUARAB, C. DEMANGEAT,A. MOKRANI

(3), 365-372


Magnetic Phase Diagram of N u u , S i , i n High Magnetic Field V. IVANOV, L VINOKLJROVA, A. SZYTUIA and A. 7XGMUNT, 3: A&YS Cmpd., 1993,191, (l), 159-163 The high field magnetisation and AC susceptibility of NdRh,Jh,Si, compounds were studied up to 140 kOe and the magnetic phase diagram was obtained as a function of concentration, x, and magnetic field. Increases in Y and in magnetic field caused changes in the magnetic properties of the NdRh,&u~i, compounds. A difference between values determined by neutron dfiaction and magnetic measurements was observed.

Magnetism and Growth of Ultrathin GI Films Grown Epitaxially on Ru(OOO1) c. LIU and s. D. BADER, J. Magn. 6 Magn. Muter.,

Ultrathin Co films were found to grow pseudomor- phicaUy on Ru(OOO1) at mom temperature in an island suucture, by evaporation h m a resistively heated Co wire in UHV. The expanded Co lattice relaxed to its bulk spacing after a 500°C anneal. No ferromagnetic hysteresis loops were detected in the first four Co monolayer equivalents (MLE), possibly due to super- paramagnetic effects, but ferromagnetic hysteresis loops with in-plane easy axes of magnetisation occurred for film thicknesses > 4 MLE.

1993, 119, (1&2), 81-86

Symmetry of the Gap in Superconducting URu,Si, K. HASSEIBACH, J. R. KIRTLEY and J. FLOUQVET, Phys. Rev. B, 1993,47, (l), 509-513

Synthesis and Structural Characterization of a Layer-Segregated Platinum-Ruthenium Cluster Complex that Exhibits Selective Coordination and a High Activity for the Catalytic Hydrogenation of Diphenylacetylene R. D. ADAMS, Z. LI, P. SWEPSTON, W. WU and J. YAMAMOTO, 3 Am. Chem. Soc., 1992, 114, (26), 10657-10658 The complex Pt,RuJCO),,(CI-H),(p3-H) w a s obtained in 83% yield &om the reaction of Ru,Pb(CO),, with H (1 a m ) in a refluxing heptane solution. The alkyne PhC,Ph was found to exhibit a co-ordination preference for a tri-Ru site in the monoalkyne derivative and also was highly active in the catalytic hydrogenation of PhC,Ph to (a-stilbene, Ph(H)C=C- O P h . The structure of this Pt-Ru complex consists of three mangular layers of nine metal atoms arranged in the form of a face-shared bioctahedron. The central layer consists of three Pt atoms while the outer layers are pure Ru.

New Molecular Superconductor,

H. KOBAYASHI, K. BUN, T. NAITO, R. KATO and A.

A new superconductor [MqEbN [pd(dmit)J, (where dmit is 4,5-dimercapto-l,3-dithiole-2-thione) was isolated with T, = 4 K at 2.4 kbar. X-ray studies showed that this superconductor is not isomorphous to neither a-[Me,Et,N][Ni(dmit),], nor to 5- [(CH,),NI [Pd(dmit),],. Its insulating phase emerged when the superconducting state was suppressed at high pressure.

[Me,E@I [Pd(dmit),ll

KOBAYASHI, chem. ,?A#. &n., 1992, (lo), 1909-1912

A Novel Chain Compound Composed of

Benzoflnone

The specific heat in the superconducting state of the heavy-fermion compound URu,Si, was modelled by

overall agreement between the modelling and exper- considering all symmeny-allowed gap functions. The Rhodium(11) PiValate Dimer and 194-

hem suggests a gap symmetry of either E. (1,l) or B,, with one or two lines of zeros, respectively.

M. HANDA, A. TAKATA, T. NAKAO, K. KASUGA, M. MIKURIYA and T. KOTERA, Chem. Lett. Jpn., 1992, (lo), 2085-2088 A chain complex [Rh,(O,CCMe,),.BQI. (I) (BQ = 1,4&nzoquinone) with the I&@) pivalate dimen con-

Preparative and Structural Chemistry of nected by the bifunctional ligation of the pquinone Chiral P,N-Bidentate Complexes of through its carbony1 0 or C=C double bond, was pre- Palladium(II) and Platinum(I1) pared by the reaction of Rh(I1) pivalate dimer

&(O,CCMe,), (II) with BQ in hexane. X-ray crystal

CHEMICAL COMPOUNDS

A. ALBINATI, F. JJANZA, H. BERGER, P. S. PREGOSIN, stIllctcve sNdies of showed that its suucture

H. RiieGGER and R. w. K m Z , Chem., 1993,322 is formed by an alternated arrangement of (n) and BQ, (4), 478486 The valine-derived chiral (L) P,N-bidentate ligand @-CH,C6H,),l'CH,CH(Pri)NHCH,C,H,) (I), PdCI,(I) (2) and PtCI,(l) (3) complexes, and the deprotonated dimeric compound [Pt(l-H)CI], (4), as well as the iodo analog of 3, were prepared. The results are discussed with the help of molecular mechanics calculations and solid-state "P-NMR methods which are shown to be useful for deter- mining 3-D structures of metal complexes in solution. The complexes exhibited different solution vs solid-state structures. The chiral pocket offered by the chelating ligand is likely to be rather flexible.

Magnetic Ordering in the New Ternary Stannide UsRh,Snls

GRAVEREAU and J. ETOURNEAU, 3 Magn. & M a p . Muter, 1993,118, (1 & 2), 187-192 Studies of structural and magnetic properties of U,Rh,Sn,,, which melts non-congruently, showed that it crystallises in the cubic Yb,Rh,Sn,,-type structure with a = 9.6416 A and it undergoes a magnetic transition near 17.5 K. At low temperature, U,Rh,Sn,, had an enhanced electronic specific heat coefficient.

F. MIRAMBET, B. CHEVALIER, L FOURNES, M. J. BESNUS, P.


Building Blocks for Polymetallic Ruthenium(lI) and Osmium(n) Polypyridine Luminophores s. K. SAHNI, M. G. B. DREW, T. w . BELL and B. s. BRUNSCHWIG,J. Chem. soc., Chem. Commun., 1993, (2), 123-125 X-ray crystallographic studies were performed on the three mixed ligand complexes of Ru and Os, prepared by refluxing aqueous ethanol solutions of cis- [Ru(bpy),Cl,] or cis-[Os(bpy),Cl,] and an excess of the tridentate ligand for 6-28 h under N,, and then precipitated as hexafluorophosphate salts. The complexes, of typical formula [Ru(bpY),bpW [PF61p PPY = 2,2’-bipyridine; bpaH = bis@icolyl)amine], have a “dangling” pyridine ligand and a luminescence life- time comparable with that of [Ru(bpy),]”.

Stabilizing of the RU: Core. Use of Highly Charged Ligands such as Sulfate and Phosphate F. A. COTTON, T. DA-ITA, L. LABELLA and M. SHANG, Inorg. Chim. Acta, 1993, 203, (l), 55-60 The new Ru~(I1,III) phosphate complex, K.,[Ru,(HPO,),(PO,)(H,O),] (l), has been prepared by a new synthetic route starting from an Ru,(II,III) carbonate complex to Ru,(II,III) sulphate and phosphate complexes, which were further transformed by electrochemical oxidation to the corresponding Ru2(III,III) complexes. Magnetic susceptibility measurements on &[Ru,(SO,),(H,O)$ at 10-300K confirmed the assignment of the ground state as one arising from an unusual configuration.

ELECTROCHEMISTRY Oxidation of Glucose at Electrodeposited Platinum Electrodes C. P. WLLDE and M. ZHANG, 3 Elecmanal. Chem., 1992, 340, (1 and 2), 241-255 Studies of the oxidation of glucose at low concentrations at electrodeposited Pt electrodes in 0.1 M HClO, were performed using an electrochemical quartz crystal microbalance (EQCM). Adsorbate, which derived from glucose through the removal of features associated with the presence of adsorbed anions in the background electrolyte, occurred in the region of potential which gave adsorbed H.

Reductions of Nitrite and NO on Pt Single Crystal Electrodes in Alkaline Solution s. YE, H. HATTORI and H. KITA, Ber. Bunsenges. Phys. Chem., 1992,96, (12), 1884-1886 The reductions of nimte and NO on Pt single crystal electrodes were studied by a voltammetric method in alkaline solution. The reductions of nitrite and NO were very structure sensitive in alkalme solution and proceeded exclusively in a potential region of 0 . 3 4 5 V (RHE) at pH > 8. Product analysis and the pH dependence showed direct reduction of nitrite and NO to NH, occurring on Pt(100) in alkaline solution with an efficiency of > 80%.

Impedance Measurements of Platinum Electrodes on a Solid Protonic Conductor

T. A. WHEAT and P. G. KOMOROWSKI, Solid State Ionics,

Impedance measurements were performed on an electrochemical system consisting of a Pt-paste electrode, a protonic conductor, hydronium-NASICON electrolyte, and a NJHJI-I,O gas phase, at room temperature. Dramatic changes in the electrode impedance with H partial pressure were shown. A comparison of the Pt-paste elemode morphology and reactions, with those of Zr0,-based cells is given. A rise in diffusion- controlled effects at low H partial pressure is seen.

Cyclic Voltammetric Investigation of the Cu- Histidine System at Platinum Conventional and Microelectrodes s. DANIELE and M. J. PENA, Ekcmchim. Acta, 1993,38,

Cyclic voltammetric studies of the reduction of C u m in solutions containing histidine (L) at Pt electrodes of conventional and microscopic size showed that the behaviour of the Cu-histidine system at the Pt working electrodes depended on the nature of the supporting electrolytes. When there was insufficient amount of ligand, LCu(I1) I 2, the voltammetric studies recorded with the macroelectrode displayed splitting or drawn out curves.

Methanol Oxidation at Carbon Supported Pt and Pt-Ru Electrodes: An on Line MS Study Using Technical Electrodes s. WASMUS and w. VIELSTICH, J. Appl. Electrochem.,

The oxidation of MeOH at highly porous Pt and Pt- Ru C-base electrodes, prepared by reduction of chloroplatinic acid and Ru(II1) chloride with K formate in the presence of the C slurry and bonded with PTFE was studied in 0.05 M H,SO, under acid methanol fuel cell conditions, by a combination of cyclic voltammetry and on line MS, which was found to be a very suitable method, especially for C”-labelled MeOH. Pt(5% on Norit BRX) and Pt-Ru (40/60; 30% on Norit BRX) were used as the C-supported catalysts. Pt-Ru showed the best performance.

The Mechanism of Electrocatalytic Hydrogenation of Organic Molecules at Palladium Black Cathodes S. J. C. CLEGHORN and D. PLETCHER, Elecrrochim. Acta, 1993, 38, (2/3), 425-430 The range of hydrogenation reactions possible at a Pd black cathode, prepared by electrodeposition onto graphite in an acid chloride bath, was assessed by voltammetry at rotating and stationary disc electrodes. Studies of the mechanism for the electrocatalytic hydrogenation of organic molecules at this cathode in MeOWethanoic acid showed that a Pd(H) species is the key intermediate and its electrogenated form causes reduction of the organic molecules.

S. F. CHEHAB, J. D. CANADAY, A. K. KURUKOSE, A. AHMAD,

1993, 59, (l), 125-132

(2/3), 165-174

1993, 23, (2), 120-124


Mechanism of Deuterium Cracking in Palladium D. SUN, Y. LEI, Y. CHEN, J. wu and Q. WANG, Acta MetaZl. Sin., 1992,28, (lo), 456-460 Optical and transmission electron microscopy studies of D, cracking in Pd after 290 h electrochemically D charging showed an increase in the density of dislocations in well-annealed Pd from 10*/cm2 to above 1 O'z/cmz, and a large amount of bubble-like structure or cracks. XRD data showed that the lattice constant of Pd increased fiom 0.3890 to 0.4034 nm. The mechanism of D cracking was considered to be the formation of D, which resulted from the segregation and recombination of D atoms around dislocations.

Electrochemistry of Colloidal Palladium. An Experimental Study of Sol Formation and Electrocatal ysis A.M.T.VONDERPWI-I-EN, ].-w. G. D E B A K K E R ~ ~ L. G. J. FOKKINK, 3 Electrochem. soc. , 1992, 139, (12),

Small colloidal Pd particles were formed in aqueous solution by electroless reduction of PdC&-- species by hydrophosphorus acid, both in the presence and absence of polymer. The presence of H,O-soluble polymers, such as polyvinylalcohol (PVA) and polyvinylpyrrolidone improved the colloid-chemical stability against flocculation and stabilised the particle size of the sols. PVA-stabilised Pd sols were highly cat- alytical for electroless Ni deposition, in contrast to conventional SnPd colloids.

Direct Electrosyntbesis of Halo and Mixed- Halo Complexes of Palladium(II and IV) by the Dissolution of a Sacrificial Palladium Anode in Aqueous Medium M. c. CHAKRAVORTI and G. v. B. SUBRAHMANYAM, Polyhedron, 1992, 11, (24), 3191-3195 Chloro and bromo complexes of Pd(I1 and IV), such as M,[PdX,] and M,[PdXJ (M = Rb, Cs, NH, and (CH,),N; X = C1 or Br), were elecwsynthesised rapidly in a single-step method by the dissolution of a Pd foil anode in chloride or bromide containing media. Electrolysis of dilute HX solution in the presence of pyridine, 2,2'-bipyridyl or 1,lO-phenanthroline yielded non-electrolytes, such as trans-[PdX,(py)J.

Electrode Kinetics of Oxygen Reduction at Carbon-Supported and Unsupported Platinum MicrocrystallitelNafionR Interface A. PARTHASARATHY, s. SRINIVASAN, A. J. APPLEBY and C. R. MARTIN, 3. Electroanal. Chem., 1992, (1 and 2), 10 1-1 21 Electrode kinetics of 0 reduction at the Pt micro- crystallite/NafionR interface was studied as a function of temperature and pressure, using porous gas-dfi- sion electrodes containing unsupported Pt or WC, in proton exchange membrane fuel cells, and H, and 0, as reactants. At current densities of 1-1000 &an2 the Tafel slope was -60 mV per decade and was independent of temperature and 0, pressure.

3475-3480

Kinetics and Mechanism of the Substitution Reaction of Ethylene Diaminetetra- acetatoruthenate(II1) with Cyanide in Aqueous Solutions M. M. TAQUI KHAN, D. CHATTERJEE, H. C. BAJAJ, K. N . BHATT and s. SANAL KUMAR, Indian 3 Chem., 1992, 31A, (9), 714-715 Studies of the kinetics of the ligand substitution of Rum (EDTA)/(H,O)- (EDTA = ethylenediamine- tetraacetate anion) with CN- were performed spec- trophotomemcally as a function of ligand concentration, pH (5.C11.0) and temperature (20-5OoC). The kinetic and activation parameters were consistent with an associative interchange mechanism. The substitution reaction was studied at four Merent temperatures.

Molecular Structure and Electrochemistry of Ru,(dpf),(CdXJI,), (dpf = N,N'- Diphenylformamidinate Ion): A Novel Ru(III)-Ru(III) Dimer J. L. BEAR, B. HAN and s. HUANG, 3. Am. Chem. Soc.,

The synthesis, structural characterisation, and spectroscopic and electrochemical studies were performed on the novel Ru? title complex. The Ru complex (1) was obtained from the reaction of Ru,(dpf),Cl with excess LiC=CC,H, in THF under Ar at room temperature. The red solution was opened to air, and the residue was dissolved in CH,Cl,. The product was purified on a SiO, gel column, and after evaporation of CH,CI, (1) was obtained in - 30% yield.

1993,115, (3), 1175-1177

Effect of Composition on the Point of Zero Charge of RuO,+TiO, Mixed Oxides L. A. DE FARIA and s. T R A S A ~ , 3 Electroanal. Chem.,

Studies of RuO,+TiO, mixed oxides prepared by thermal decomposition of RuCl,+TiCl, at 450°C were carried out. The point of zero charge (pzc) was measured by potentiomemc titration of oxide suspensions in KNO, solution. The charge-pH curves were transformed into capacitance values which were used at the pzc to estimate in-situ the real surface area and the inner layer capacitance. The rude form of TiO, has a pzc close to that of RuO, which results in a pzc vary- ing very little between 40 and 100% RuO,.

1992,340, (1 and 2), 145-152

PHOTOCONVERSION A Study of Ultraweak Luminescence in Evolution of Oxygen at Pt Electrodes z. WANG, x. JIN, s. CAI, Y. LIU and A. FUJISHIMA, Electrochim. Acta, 1993, 38, (2/3), 267-269 Studies of ultraweak photoemission at a Pt electrode in aqueous solutions containing no luminescer were made using a photon counter. Weak photoemission accompanied 0 evolution at the Pt electrode in solutions H,SO, or KOH, and borate or NaHCO, buffer systems. It is suggested that the uluaweak photo-emission comes &om the recombination of singlet 0.


Generation of Homogeneous Rhodium Particles b Photoreduction of Rh(II1) on TiO, Colloi& Grafted on SiO, A. FERNANDEZ, A. R. G O N Z h Z - E U P E , C. REAL, A. CABALLERO and G. MUNUERA, Laflgmuir, 1993, 9, (I), 121-125 Spectroscopic studies of photochemical deposition of metallic Rh on three TiOJSiO, samples, containing 3,6 and 12 wt.% TiO,, prepared by the reaction of OH groups and H,O on the SiO, surface with Ti(OCH(CH,),), showed the formation of Rh- TiOJSiO, composite materials. Small metallic particles with very narrow size distributions were formed which depended on the amounts of TiO, grafted on the SiO, and on the initial concentration of Rh.

Visible Light Induced Hydrogen Production with Cu(II)/Bi,O, and Pt/Bi,O,/RuO, from Aqueous Methyl Viologen Solution

IAN and M. v. c. SASTRI, Int. J . Hydrogen Energy, 1993,

The oxide semiconductor y-Bi,O, was doped individually with Cu(II) ions, or loaded with Pt a n d or RuO, (0.5 at.%) and used as a fine powder for photocatalytic production of H, fiom H,O in the presence of methyl viologen (MV’? as an electron relay. The aqueous slurry of the catalyst was irradiated for 90 min in the presence of MV” resulting in generation of 0.79 and 0.66 ml of H, by 4 at.% Cu(II)/Bi,O, and PtlBi,OJRuO,, respectively.

Study of Photoelectrochemical Cells: Micellar Effect on the [R~(bpy),]~’-Sensitized Photoreduction of Dyes by NhEDTA

Transition Met. Chem., 1992, 17, (6), 506-508 Studies on photoelectrochemical cells using [Ru(bpy),l2* as sensitiser in the presence of Na,EDTA reducing agent along with various dyes in various types of anionic, neutral or cationic micellar media were performed in order to find out the ability of the Ru sensitiser to generate photocurrents and photo- voltages. The yield of photocurrent was found to be dependent upon the dye and micellar medium.

P. MARUTHAMUTHU, K. GURUNATHAN, E. SUBRAMAN-

18, (l), 9-13

S . UNGAMURTHY, B. SETHURAM and T. N. RAO,

Photoresponsive Electrode Based on the Reaction between Oxygen and the Excited Ru(bpy)F Complex Incorporated in a Coated Nafion Film

and M. KANEKo, Elecrrochim. Acra, 1993, 38, (I),

A photoresponsive electrode was prepared by coating a Nafion film on an InSn oxide (ITO) electrode having the Ru(bpy),” complex in the film. A photocurrent was induced at the coated electrode dipped in an aqueous electrolyte in the presence of 0. Viologen molecules present as a solute or as the second film on the top of the Nafion[Ru(bpy);T film increased the induced photocurrent by - a factor of 2.

Y. UENO, K. YAMADA, T . YOKOTA, K. IKEDA, N. TAKAMIYA

129-133

Formation of a Stabilized Coordinatively Unsaturated Metal Carbonyl Cluster, H$u,(CO),,, by Photochemical Reaction of €I&,( CO),, Adsorbed on the Surface of Silica S. YAMAMOTO, K. ASAKURA, K. MOCHIDA, A. NITTA and H. KURODA, 3 Phys. Chem., 1993,97, (3), 656-660 Studies of the photochemistry of H,Ru,(CO),, ( 1 ) adsorbed on the surface of SiO, showed that during irradiation by W-visible light, ( 1 ) lost one CO lig- and, giving selectively co-ordinatively unsaturated H,Ru(CO),, on the SiO, surface. The initial photo- product, H,Ru,,(CO) ,, interacts weakly with surface hydroxyl groups, which are the only functionality available to act as a stabilising ligand.

ELECTRODEPOSITION AND SURFACE COATINGS Thermal Stability of a Platinum Aluminide Coating on Nickel-Based Superalloys H. M. TAWANCY, N. SRIDHAR, B. S . TAWABINI, N. M. ABBAS and T. N. RHYS-JONES, J. Mater. Sci., 1992, 27, (23), 6463-6474 The thermal stability of a Pt aluminide coating on the directionally solidified alloy MAR M 002 and its single crystal version alloy, SRR 99, was studied at 800,1000 and 1100°C. The morphology of the coating was characterised. In the as-deposited state the coating was two layers, most Pt was in the outer coating layer, which consisted of a fine dispersion of PM, in a manix of p-(Ni, Pt)AI containing Co and Cr.

Interdiffusion of the Aluminized and Pt-Aluminized Coatings on MAR-M247 Superalloy K.-L. m and c.-M. HWANG, sut$ Coat. Technol., 1992,

The interdiffusion behaviour of Pt-aluminised (1) and aluminised (2) coatings were investigated on MAR-M247 superalloy. A NiAl phase formed for the (2) coating, while the PtA1, phase was identified as well as the NiAl phase for coating (1). It was concluded that Ni diffuses outwards for coating (2) but for coating (1) Pt acts as the diffusion media, which enhances the outwards diffusion of Ni and the inward diffusion of Al to form the two phases.

The Roles of the Ruthenium Concentration Profile, the Stabilizing Component and the Substrate on the Stability of Oxide Coatings

NIKOUC and R. T. ATANASOSKI, p Electroanal. Chem., 1992,339, (1 and 2), 147-165 Electrochemical studies of oxide coatings with variable concentration profiles of RuO, as the active component, were performed on components obtained through a combination of separately applied layers of RuO,, TiO,, IrO,, RuO,”TiO,, and RuO,’IrO, on Ti and glassy C substrates. Both the stability of the coatings and their related charge depended strongly on the sequence of layers in the Ru0,-TiO, coating.

56, (l), 81-87

V. M. JOVANOVIC, A. DEKANSKI, P. DESPOTOV, B. Z.


APPARATUS AND TECHNIQUE Mediated Micro-Glucose Sensors Using 2 pm Platinum Electrodes

SUZUKI, T. TAKEUCHI, E. TAMIYA and I. KARUBE, Elecnoanalysis, 1992,4, (9), 859-864 Glucose-oxidase (GOD) and glucose-dehydrogenase (GDH) sensors, immobilised in a photocrosslinkable polymer, were fabricated on a cylindrical Pt microelectrode of 2 pm diameter, and characterised by using 1,4-benzoquinone and ferricyanide as electron mediators, respectively. For the GOD micro-glucose sensor, a calibration plot was obtained that was linear up to - 40 mM glucose, which is superior to values obtained with a disk electrode of 1 mm diameter.

"rimethylamine-Sensing Mechanism of Ti0,- Based Sensors. 1. Effects of Metal Additivea on Trimethylamine-Sensing Properties of TiO, Sensors Y. TAKAO, Y. IWANAGA, Y. SHIMIZU and M. EGASHIRA, Sens. Acruawrs B, 1993,10, (3), 229-234 Studies were performed of the effect of Pt, Pd, Rh, Ru, In or Au additives on the trimethylamine (TMA)- sensing properties of TiO,. The sensitivity to TMA was enhanced by the addition of 0.5 wt.% Ru, 2.0% In or 0.5 wt.% Au, while the addition of 0.5 wt.% Pt, 1.5 wt.% Pd or 1.5 wt.% Rh lead to a decrease in the sensitivity. Ru acted as a stronger electron donor from TiO, than expected from its work function.

K. YOKOYAMA, K. NAKAJIMA, S . UCHNAMA, S . SUZUKI, M.

HETEROGENEOUS CATALYSIS The Catalytic Effect of Platinum on the Oxidation of Carbon Fibres R G. IACOCCA and D. J. DUQUETTE, 3 M m . Sci., 1993,

The effects of Pt on the oxidation behaviour of PAN- based 5C carbon fibres has been investigated at 500, 550 and 600°C in air. Fibres oxidised in Pt holders had a higher activation energy than those oxidised in SO,. The pre-exponential term for fibres oxidised in Pt was six orders of magnitude larger than the fibres oxidised in the SiO, holders. Spheres formed along the longitudinal axis of many fibres and one fibre bifur- cated with a sphere forming on each remaining fibril.

28, (4), 1 11 3-1 11 9

Isomerization of Xylene Isomers on a PtRe- H-Mordenite Catalyst A. K. A B O U L & ~ , s. M. ABDEGHAMID and F. M. ABDEL HAY, A". C a d . A: Gen., 1993,93, (2), 131-140 Studies of the isomerisation of xylene isomers performed on a 0.35 wt.%Pt-0.35 wt.% Re/H-mordenite catalyst in a pulse catalync microreactor showed the presence of para-xylene as the highest C8 aromatic component of the hydroconversion of any xylene isomer, whereas orrho-xylene was the lowest. Trimethylbenzenes and ethylbenzenes were not detected in the reaction products. The results indicate an excellent shape-selectivity for paru-xylene production on the PtRe/H-mordenite catalyst.

Catalytic Activity and Characterization of Pt/SiO, Catalysts Prepared by the Sol-Gel Method M. ASOMOZA, T. LOPEZ, A. ZAMALLOA, R GOMEZ and E. GARCIAFIGUEROA, New J. Chem., 16, 1992, (lo),

Pt/SiO, catalysts were prepared by the sol-gel method by adding [PtCIJ* to tetraethoxysilane, followed by hydrolysis and condensation. The addition of H,PtC&.6HZ0 during the formation of the gel resulted in solids with surface area of up to 1,100 m2/g. The catalysts with a low metal concentration were active for the hydrogenation of alkenes but not for the hydrogenation of aromatics. Deactivation studies showed that sol-gel Pt catalysts were more resistant to poisoning by thiophene than impregnated ones.

High Catalytic Activity of Platinum-ZSM-5 Zeolite below 500 K in Water Vapor for Reduction of Nitrogen Monoxide H. HIRABAYASHI, H. YAHIRO, N. MIZUNO and M. IWAMO- TO, Chem. La. a n . , 1992, (ll), 2235-2236 A pronounced catalytic activity of Pt ion-exchanged ZSM-5 (SiO,/Al,O, = 23.3) zeolite is reported below 500 K for the selective reduction of NO by ethene even in the presence of 8.6 MI.% of H,O vapour. The most active temperature of Pt-MFI-97 (cation-zeolite structure-degree of exchange) in the absence of H,O vapour was 485 K and the conversion into N, and N,O were 18% and 36%, respectively. The conversion of C,H, at 485 K on Pt-Mm-97, Fe-MOR-7 1 and Cu-MFI-105 were 100,4 and 1 %, respectively.

959-963

Non-Faradaic Electrochemid M&cation of Catalytic Activity. M. The Case of Methane Oxidation on Platinum P. TSIAKARAS and C. G. VAYENAS, 3 catal., 1993, 140, (l), 53-70 The catalytic activity of Pt for CH, oxidation increased reversibly by up to 7000 % by depositing polycrystalline Pt films on Y,O,-doped ZrO,, and by polarising the Pt-solid electrolyte interface. The catalytic rate is increased by supplying and by removing 0'- to or from the Pt catalyst through the gas-impervi- ous solid electrolyte. The rate of CH, oxidation depended exponentially on catalyst potential and work function, e$, over wide (up to 0.8 eV) e$ ranges.

Reactions of Labelled Hexanes on Pt- wo,/A120, Catalysts J. M. FARBOTKO, F. GARIN, P. GIRARD and G. M A I R E 3 CataL, 1993, 139, (I), 256-267 Hexane hydrocracking and isomerisation on Pt- WO,/AI,O, catalysts (Pt:W = l:l), prepared by different methods, and studied by isotopic tracer measurements, showed that the systems catalysed the isomerisation with low selectivity. The reaction proceeded via classical cyclic and bondshift mechanisms. No correlation between the relative contribution of the cyclic mechanism and the non-selective hydrogenolysis of the methylcyclopentane was found.

Platinum Me& Rev., 1993,37, (2) 113

Highly Selective Pt-Cr/C Alloy Catalysts for Single-Step Vapour Phase Hydrogenation of Phenol to Give Cyclohexanone s. T. SRINIVAS and P. KANTA R A O , ~ Chem. SOC., Chem. Commun., 1993, (l), 33-34 Studies of the catalytic activity of Pt-Cr/C catalysts during the single-step vapour phase hydrogenation of phenol showed them to be active for the hydrogenation of phenol with total selectivity to give cyclohexanone. Alloying of the 5 wt.%Pt/C with Cr improved the cyclohexanone selectivity from 84 to 100% in the hydrogenation without giving any side products. The H uptake on the alloy catalyst correlated directly with the phenol conversion.

Effects of Alcoholic Solvents on the Formation of Cyclohexanones in the Hydrogenation of Phenols over Pd-C Catalysts M. HIGASHIJIMA and s. NISHIMURA, Bull. Chem. SOC.

Studies were performed of the hydrogenation of phenol and isomeric cresols in cyclohexane and t-pentyl alcohol (t-PeOH) as solvents with a commercial P d C and acid-treated P d C (PICIA) catalysts under H pressure at 120'C. In both catalysts, the maximum yields of the cyclohexanone intermediates as well as the hydrogenation rates of the phenols decreased markedly in t-PeOH compared with hydrogenation in cyclohexane.

'JDTz., 1992, 65, (1 l), 2955-2959

The Reactivity of High Oxygen Coverages on Pd(ll0) in Catalytic CO Oxidation

(1/2), 14-22 The catalytic oxidation of CO on a Pd( 1 10) surface was studied during CO titration and under steady- state conditions at 10-'Torr. The titration studies with the 0-saturated Pd( 1 10) surface showed a change in the reaction mechanism from a uniform reduction of the 0 coverage at high temperatures,= 400 K, to a hole-eating mechanism at low temperature. High 0 coverages inhibited the rate of CO, production which was atnibuted to a lowering of the CO residence time and to a reduction of the CO sticking coefficient.

Effect of Sulfur on the Performance and on the Particle Size and Location of Platinum in Ptw, Hexane Aromatization Catalysts

S. LADAS, R IMBML and G. ERTL, SU?$ &., 1993,280,

G. B. McVICKER, J. L. KAO, 1. J. ZIEMIAK, W. E. GATES, J. L. ROBBINS, M. M. J. B C Y , S. B. RICE, T. H. VANDERSPURT, V. R CROSS and A. K GHOSH,J catd., 1993,139, (I), 48-6 1 When S was introduced to a working PtML hexane aromatisation catalyst in the form of thiophene, it functioned as a very potent poison which reduced the number of Pt sites accessible within the channels of the KL zeolite. However, the intrinsic catalytic activity and selectivity of in-channel Pt sites were not significantly modified by the presence of S on the catalyst. Extremely low thiophene feed S concentrations at 50-200 wppb accelerated Pt agglomeration.

Phenylawtaldehyde and Carbon Monoxide as Effective Additives for the Selective Hydrogenation of Cyclooctadienes to Cyclooctene over Palladium Catalysts M. HIGASHIJIMA, H. s . MAN and s. NISHIMURA, Bull. Chem. SOC. JPn., 1992,65, ( l l ) , 2960-2965 Isomeric 1,5-, 1,4- and 1,3-cyclooctadienes (COD) were hydrogenated with phenylacetaldehyde (FA)- or CO-treated Pd black in tetrahydrofixan at 25°C and atmospheric pressure of H. Catalysts poisoned by PAA greatly promoted isomerisation of 1,5-COD to 1,4-COD, while the rate of hydrogenation of 1,4- and 1,3-COD decreased.

n-Butane Hydrogenolysis as a Probe of Surface Sites in Rhodium Metal Particles: Correlation with Single Crystals D. KALAKKAD, S. L. ANDERSON, A. D. LOGAN, J. P&A, E. J. BRAUNSCHWEIG, c. H. F. PEDEN and A. K. DATYE, J. Fhys. Chem., 1993,97, (7), 1437-1444 The effect of particle sue and pre-oxidation on the hydrogenolysis activity and product selectivity was studied during n-butane hydrogenolysis, on Rh metal catalysts supported on Al,O, and Si,O with the metal particle size varied (from < 1 to 5 > nm) by changing the metal loading from 0.03-7.2 pmol of Rh/mz of support. The ethane selectivity of the highly dispersed Rh was very different from that of the low index single crystal surfaces of Rh. As particle size was increased, the selectivity of the catalysts approached that of Rh(ll1).

Zirconium-Based Intermetallics as Heterogeneous Catalysts for the Fischer- Tropsch Reaction: In. Zr-Co-Ni-Cu and Ru Catalysts

TERBOTTOM and I . R. HARRIS, J. Chem. Technol. Biotechnol., 1992, 55, (4), 375-378 Intermetallic alloys of type Zrs,J4&ssz, where 0 I x S O , were prepared by Ar arc melting. M and N are combinations of Co, Ni, Cu and Ru. The alloys were powdered by H decrepitation, after which they were used in this form as catalysts. The H,/CO reaction was performed in a semi-micro-tubular flow reactor.

A. F. Y. ALSHAMMARY, 1. T. CAGA, A. Y. TATA, J. M. WIN-

HOMOGENEOUS CATALYSIS Palladium-Catalyzed Aldol-Type Condensation by Enol Esters with SnCI, Y. MASUYAMA, T. SAKAI and Y. KURUSU, Tetrahedron

En01 esters caused aldol-type condensation with aldehydes in the presence of PdCI,(PhCN),.SnCl, catalyst at 50°C in acetonitrile to give (6-a$-unsaturated carbonyl compounds. Cyclic enol ester, such as u- angelicalactone, also reacted with aldehydes under the same conditions to produce ysubstituted bacetyl- yburyrolactones and/or 5-substituted 4-acetyl-2(5H)- furanones. yButyrolactones were only obtained with arenecarbaldehydes.

Lett., 1993, 34, (4), 653-656


Palladium-Catalyzed Carbonylative Vi lation of Arylmercuric Chlorides with Jarbon Monoxide and Olefins D.-S. RYU, K.-H. SONG, J.-T. LEE and J.-I. KIM, B d . Korean Chem. SOC., 1992, 13, (4), 345-355 Arylmercuric chlorides reacted with CO and olefins in the presence of PdC1,(PPh3), catalyst, a base and CuCl,, under mild conditions, to give the corre- spondmg aryl vinyl ketones in moderate to good yields. An increase in CO pressure enhanced the yields of the desired aryl vinyl ketones. The mechanism of this carbonylative vinylation involves o*ansmetallation of the Pd(II) catalyst, CO insertion to give the aroyl Pd(I1) complex, reaction with olefins, and reoxidation of Pd(0) to Pd(I1) with CaC1,.

Catalytic Asymmetric Synthesis of Optically Active Alcohols via Hydrwilylation of Olefins with a Chiral Monophosphine-Palladium Catalyst T. HAYASHI and Y. UOZUMI, Am ApPr Chem., 1992,64,

The reaction of terminal alkenes with trichlorosilane at 40°C in the presence of 0.1 and 0.01 mol% of Pd catalyst prepared in situ from [PdCl(rr-C,H,)], and (~-2-(diphenylphosphino)-2'-methoxy- 1,l '-binaph- thy1 proceeded with unusual regioselectivity at up to 94% and with high enantioselectivity to give high yields of 2-(mchlorosilyl)alkanes and a minor amount of 1-(mchlorosily1)alkanes. Oxidation of C-Si bond gave optically active alcohols with enantiomeric purity ranging between 94% and 97% ee.

The Palladium-Catalyzed Cross-Coupling Reaction of Enol Acetates of a-Bromo Ketones with l-Auren 1-

and 'heir Enol Acetates s. ABE, N. MIYAURA and A. SUZUKI, Bull. Chem. SOC. Jpn., 1992,65, (lo), 2863-2865 Pd-catalysed cross-coupling reaction between alkyl-, aryl- or 1-alkenylboron reagents with enol acetates of a-bromo ketones using Pd(PPhJ, catalyst readily produced stereodefined enol acetates of ketones. Hydroboration of alkene with 9-borabicyclo- [3.3. llnonane followed by coupling with Q-2-ethoxy- 1-bromoethene gave the enol ether of aldehyde.

Synthesis of Phthalides through Palladium- Catalysed Heteroannulation of Acetylenic Compounds N. G. KUNDU and M. PAL, J. Chem. SOC., Chem. Commun., 1993, (l), 86-88 The heteroannulation of acetylenic compounds in the presence of (PPh,),PdCl, and Pd(OAc), catalysts, yielded phthalides [ 1-(3H)isobenzofuran-3-ones] as major products and isocoumarins as minor products. The reactions were carried out by heating a mixture of o-iodobenzoic acid and acetylenic compound in the presence of the Pd catalyst, Cu(1) iodide and a base in dimethylformamide.

(12), 1911-1916

Com ounds; A Faci 1 e Synt ' 9!-9 esis Or of YZbron etones

Formation of 2-Imino-1,3-Oxathioles and 2(3H)-Oxazolethione by the Rhodium(I1) Acetate-Catalyzed Reaction of a-Diazo- carbonyl Compounds with Isothiocyanates T. IBATA and H. NAKANO, Bull. Chem. SOC. m., 1992,

Studies of Rh,(OAc), catalysed reaction of various a- diazocarbonyl compounds with alkyl, phenyl and ben- zoyl isothiocyanates showed good yields of 2-imino- 1,3-0xathioles and a by-product 2(3H)-ox-azolethione, which was only produced in the reaction of dia- zodimedone with methyl isothiocyanate. The preferable formation of thiocarbonyl ylide was explained by heat of formation and frontier molecular orbital calculations.

65, (1 l), 3088-3093

Rhodium( 11)-Catalyzed Cyclization of 2- Alkynyl 2-Diazo-3-oxobutanoates as a Method for Synthesizing Substituted Furans A. PADWA and F. R. KMDER, J. Org. Chem., 1993, 58,

Studies of a series of 2-alkynyl 2-diazo-3-oxobutanoates treated with a catalytic quantity of Rh(I1) acetate showed the synthesis of furo[3,4-c]furans in good yield. The reaction occurred by addition of a Rh-stabilised carbenoid onto the acetylenic rr-bond to produce a vinyl carbenoid which cyclises onto the adjacent carbonyl group to produce the furan ring.

Electronic and Steric Control in Carbon- Hydrogen Insertion Reactions of Diazoacetoacetates Catalyzed by Dirhodium(I1) Carboxylates and Car box a mid es M. P. DOYLE, L. J. WESTRUM, W. N. E. WOLTHUIS, M. M. SEE, w. P. BOONE, v. BAGHEM and M. M. PEARSON,J Am. Chem. SOC., 1993, 115, (3), 958-964 Studies of the unique capabilities of Rh(I1) carboxylates and carboxamides in modifyrng regiocontrol in C-H insertion reactions were performed in order to idennfy the electronic and steric factors which control regioselectivity. 2,3,4-Trimethyl-3-pentyl diazoace- toacetate formed y-lactone products from insertion into primary and tertiary C-H bonds in a statistical distribution (61:39) with diRh(I1) tetrakis(peduorobutyrate), but only tertiary C-H insertion was observed with diRh(I1) tetraacetamide.

Highly Efficient Re ioselective Silylcarbon lation of Alkynes dtalyzed by DirhodiumKI) Perfluorobutyrate M. P. DOYLE and M. s. SHA", Organometdics, 1993, 12, (l), 11-12 Studies of the activity of R h o peduorobutyrate catalyst during silylcarbonylation of terminal acetylenes showed it to be highly effective, giving high catalyst turnovers, exceptional E:Z isomer ratios and high yield of Psilylacrylaldehydes with substantial stereo- control at atmospheric pressure, and at or below room temperature. The stereochemistry of the major isomer formed is that of cis addition.

(l), 21-28

Phtinum M e d s Rev., 1993, 37, (2) 115

Room-Temperature Catalytic H drogenation of Aromatic Hydrocarbons 6sing [(1,5- COD)RhH], as a Catalyst Precursor z. DUAN and M. J. HAMPDEN-SMITH, Chem. Muter., 1992,4, (6), 1146-1 148 [(1,5-COD)RhHl, (1) (COD = cyclooctadiene) was synthesised by the reaction of [(1,5-COD)RhCI], with LiBEt,H at room temperature in THF under N, conditions, and used as a source of 2-nm-sized Rh crystallites under mild conditions. Solutions of (1) were very stable in aromatic and aliphatic hydrocarbon solvents under inert atmosphere in the absence of H, but aromatic HC solvents were unstable in H.

Acetic Anhydride Synthesis from Meth 1 Formate Catalysed by Rhodium-Iodiie Complexes B. SEUILLET, Y. CASTANET, A. MORTREUX and F. PETIT, Appl. Cutal. A: Gen., 1993, 93, (2), 219-229 Studies of a “one pot” synthesis of acetic anhydride fkom methyl formate in the presence of a RhI,(CO), showed that it requires a two stage procedure, due to the incompatibility of the activations used to sustain the two consecutive reactions of homologation and carbonylation. In the fist stage, an alkaline iodide, LiI, was used with an accurate M:Rh ratio, to avoid acetic acid production, while in the second stage, an alkyl iodide was required to provide the synthesis of acetic anhydride.

Formation and Reaction of Acyl Substituted Nitrile Ylide through the &(OAc),-Catalyzed Reaction of a-Diazocarbonyl Compounds with Benzonitrile T. IBATAand K. FUKUSHUIA, Chew. Let?. m., 1992, ( l l ) , 2197-2200 The Rh,(OAc), catalysed decomposition of p-chloro- a-diazoacetophenone in benzonitrile in the presence of dimethyl acetylene-dicarboxylate produced 5-@- chlorophenyl)-2-phenyloxazole and dimethyl 2-@- chlorobenzoyl)-5-phenylpyrrole-3,4-dicarboxylate in 63 and 1 1 % yields, respectively. The reaction gave oxazoles and pyrrole-3,4-dicarboxyylates through the 1,5-cyclisation and 1,3-dipolar cycloaddition of the acyl substituted nitrile ylide intermediates generated by the reaction of ketocarbenoids with benzonitrile.

Rhodium(1p Trifluoroacetamide; an Excellent atalyst for Carbenoid 0 - H Insertion Reactions G. G. cox, J. 1. KULAGOWSKI, c. J. MOODY and E.-R H. B. s~~,S’len, 1992, (12), 975-976 Studies of Rh(II) acetate and trifluoroacetamide catalysts during cyclopropanation of ethyl diazoacetate with alkenes showed very rapid conversion of the diazo compound in the presence of Rh(I1) trifluoroacetamide (1) catalyst when using an intermolecu- lar insertion reaction into the 0 - H bond of 2- propanol. Catalyst (1) was found to be extremely effective for inter- and intra-molecular carbenoid 0-H insertion reactions.

Diastereoselectivity in the Osmium Tetraoxide Promoted Dihydroxylation of Chiral (E) - Gotylsilanes: Asymmetric Synthesis of Silyl- Functionalized plactones J. S . PANEKand J. ZHANG,J &g. Chem., 1993,58, (2), 294-296 Studies of the catalytic osmylation of enantiomeri- cally enriched (E)-crotylsilanes (2S,3R)-1 and (2R,3R)-2 containing a homoallylic, N-bearing stere- ocentre, using OsO, catalyst, showed good to high levels of diastereoselection generating silyl-functionalised trans-4,5 substituted y-lactones as the major diastereomers. The selectivity exhibited by the silane reagents together with the high degree of functional- isation contained in the derived y-lactones showed them to be intermediates in asymmetric synthesis.

Catalytic Oxidation of Partially and Fully Fluorinated Olefins with Osmium Tetroxide w. A. HERRMANN, s. J. EDER and w. SCHERER, Angew. Chem. Znt. Ed. Engl., 1992,31, (lo), 1345-1347 The formation of cycloadducts of partially and fully fluorinated olefins and their conversion into fluorinated diols and products of subsequent reactions in the presence of OsO, is reported, which is contrary to a previous assumption that very electron-poor olefins do not react with the OsO,. Fluoroalkenes reacted with OsO, in hexane in the presence of pyridine and N-containing bases at room temperature giving cyclic osmate(VI) esters quickly and quantitatively.

Asymmetric H drogenation of 2-Fluoro-2- alkenoic AcidYs Catalyzed by Ru-binap Complexes: A Convenient Accees to Optically Active 2-Fluoroalkanoic Acids M. SABURI, L. SHAO, T. SAKURAI and Y . UCHIDA, Tetrahedron Lett., 1992,33, (51), 7877-7880 Studies of asymmetric hydrogenation of (2)-2-fluoro- 2-alkenoic acid (1) in the presence of Ru,Cl,(binap),(NEt,) catalyst (binap = (R)- or (9- 2,2’-bis(dipheny1phosphino)- 1, 1’-binaphthyl) showed a yield of 2-fluoroalkanoic acids with high enantiomeric purities of up to 90% ee. When the (R)- binap catalyst was used, both (2)- and (E)-(l) were smoothly hydrogenated to give (R)-Zfluorohexanoic acid with comparable asymmetric induction.

Reactivity of Cp*Ru’ with Acyclic Unsaturated Hydrocarbons: A Novel Catalytic Carbon-Carbon Bond Activation Reaction R. CARRENO, B. CHAUDRET, D. LABROUE and s. SABO- ETIENNE, Orgunometallics, 1993, 12, (l), 13-14 The versatile reactivity of the electrophilic fragment Cp*Ru’, which was generated in situ through protonation of [Cp*Ru(OMe)], by CF,SO,H with 1,3,5-hexatriene, toward unsaturated acyclic hydrocarbons is described. A catalytic reaction performed with neohexene produced three different types of products: (a) neohexene oligomers, (b) 2,3-dimethyl- 2-butene and 2,3-dimethyl-l-butene in 92% yield, and (c) CH, together with C,, and C,, hydrocarbons.


Ruthenium Catalyzed Reconstitutive Condensation. Application to Functionalbed Steroid Side Chains B. M. TROST, R J. KUZAWIEC and A. HAMMES, Temhednm

bis(Tripheny1phosphe)cyclopentadienylruthenium chloride catalysed the addition of steroidal acetylenes with ally1 alcohols to introduce functionalised side chains illustrated by the construction of the side chain of ganoderic acid which is a novel angiotensin-con- verting enzyme inhibitor. The excellent chemoselec- tivity and atom economy of the Ru catalysed reconstitutive condensation make it a useful method for elaborating steroid side chains with minimal need for protecting groups.

Studies on Transition-Metal 0x0 and Nitrido Complexes. 13. Perruthenate and Ruthenate Anions as Catalytic Organic Oxidants A. J. BAILEY, w. P. G R I F ~ , s. I. MOSTAFA and P. A. SHERWOOD,horg. Chem., 1993,32, ( 3 , 268-271 The [RuOJ ion, which was generated in aqueous base at pH 1 1 from aquated RuCl,.nH,O with BrO,- as co-oxidant, catalytically oxidised primary alcohols, activated alkyl halides, aldehydes, 1,2-diols and nitroalkanes to carboxylic acids. However, the secondary alcohols and halides were oxidised to ketones, bromate being the co-oxidant.

htt., 1993, 34, (4), 587-590

FUEL CELLS A Unitized Approach to Regenerative Solid Polymer Electrolyte Fuel Cells H. P. D ~ J Appl. Electrochem., 1992,23, (l), 32-37 Unitised regenerative fuel cell data were obtained with a cell design which allows the same unit to function both as a power producer and as an electrolyser. The cell contained Pt/C and Pt/Ir/C gas diffusion electrodes on the 0 side and W C electrodes on the H side, membranes and a solid polymer electrolyte, usually used in fuel cells. The current-potential data in the regenerative electrolysis decreased with time but the fuel cell current was very stable. The membrane-electrode assemblies functioned well, and no visible corrosion was observed.

Surface and Catalytic Properties of Iron- PlatindCarbon Electmcataly&a for Cathodic Oxygen Reduction in PAFC K. T. KIM, J. T. HWANG, Y. G. KIM and J. s. CHUNG, 3. Elecmchem. SOC., 1993, 140, (l), 31-36 Studies of surface and catalytic properties of Pt-Fe catalysts were made in phosphoric acid fuel cells, on catalysts prepared by impregnation of Fe(NO,), solution into WC. The catalyst was heat-treated in a flow of Ar at 450,750 and 900"C, or this process was followed by an acid-treatment in 1 M H,SO,. With increased heat-treatment temperature, the Pt surface area measured by H chemisorption decreased rapidly due to particle sintering, an alloying effect and enrichment of Fe on the surface.

Direct Electrooxidation of Methanol on Highly Dispersed Platinum-Based Catalyst Electrodes: Temperature Effect G. h&U, 1.-M. L~GER, c. LAMY and R DURAND, J Appl.

The direct elemoxidation of MeOH in acid medium was studied on a perfluorinated Nafion membrane containing small amounts of Pt, about 1 mgkm', and other metal catalysts, incorporated by chemical reduction. Pt modified by other metals was the best catalyst to obtain oxidation potentials much more compatible with a working anode in a direct MeOH fuel cell. Ru and Sn lead to a negative shift of > 250 mV as compared to the potential obtained with pure Pt.

Platinum-Iridium Bimetal Catalyst-Based Porous Carbon Eleetrodea for H,-Cl, Fuel Cells S. M. A. SHlBLl and M. NOEL, In?. 3 Hydrogen Energy,

Teflon bonded Pt-Ir bimetal catalyst-based porous electrodes were prepared for use in H,-Cl, fuel cells. These gas d f i s i o n electrodes, fabricated by a hot pressing technique, had optimised performance at 2.5 wt.% Pt and 5 wt.% Ir, for both H, oxidation and C1, reduction reactions. The fuel cells has optimised operation at 333 K, gas pressure of 60 mm Hg on both electrodes, 5 M HCl electrolyte and interelec- w d e distance of 6 mm. Under these conditions wlt- ages of 1 .O V at current densities of 100 W c m 2 for 300 h were obtained.

E l e ~ m c h t ~ ~ . , 1993,23, (3), 197-202

1192, 18, (2), 141-147

CORROSION PROTECTION The Nature of the Passive Film on Cathodieally Modified Stainless Steels

Elecmchem., 1993,23, ( l) , 11-18 The effect of additions of platinum group metals on the composition of the passive surface layer formed on stainless steels in reducing acid media was studied. An accumulation of the platinum group metals occurred on the surface of the alloy during the period of active dissolution.

J. H. POTGIETER, W. SKINNER and A. M. HEYNS,J Appl.

CHEMICAL TECHNOLOGY Alloys of Palladium with Metals of the Platinum Group as Hydrogen-Permeable Membrane Components at High Temperahma of Gas Separation F. N. BERSENEVA, N. I. TIMOFEEV and A. B. ZAKHAROV, Inr. J Hydrogen Energy, 1993,18, ( l) , 15-18 Studies of the effect of phase composition of the binary Pd-Pt and Pd-Rh matrices in which the concentration of Pt and Rh in the uniform f.c.c. solid solution was 0-25%, were performed. The effects of dissolved H on the phase composition and mechanical properties of Pd-Pt and Pd-Rh alloys were examined. Multicomponent alloys of Pd with platinum group metals are suitable membrane materials.

Platinum Metah Rev., 1993, 37, (2) 117

ELECTRICAL AND ELECTRONIC ENGINEERING Optimization of the Tradeoff between Switching Speed of the Internal Diode and On-Resistance in Gold- and Platinum- Implanted Power Metal-Oxide-Semiconductor Devices M. F. CATANIA, F. FRISINA,N.TAVOLO, G. FEFL4,S. COFFA and S. U. CAIWISANO, IEEE Trans. Electron Devices, 1992,39, (12), 2745-2749 The effect of Pt and Au doping on the switching characteristics of the internal diode of power MOS devices was studied. The tradeoff curve between the on-resistance of the device and the reverse recovery charge of its internal diode was measured after diffusion of the metallic impurities. It is concluded that Pt implan- tation applied to power MOS device fabrication gives an improved tradeoff between dynamic and static device characteristics with respect to Au doping. High- voltage n-channel power MOS devices with a fast internal diode and a limited increase in the on-resistance were produced by this fabrication process.

Ti/Pt/Au Ohmic Contacts to n-Type ZnSe T. MIY~TIMA, H. OKIJYAMA and K. AKIMOTO, Jpn. J Appl. Phys., Pan 2 Lett., 1992, 31, (12B), L1743-L1745 A Ti/Pt/Au multilayered metal structure was found to form a nonalloy ohmic contact to n-ZnSe with an electron concentration of 1019/cm3. A specific contact resistance as low as 3.4 x104R an* was obtained for an n-type C1-doped ZnSe layer with a high electron concentration of 2 x 101q/cm3. The lower contact resistance can be ascribed to the higher reactivity and adhesion of Ti metal with the surface of ZnSe at low temperature, and to the lower work h c t i o n of Ti metal. A small improvement in the specific contact resistance was made by thermal annealing at 250°C for 5 min, which yielded the lowest value of 1.1 x lo4 Q anz. The electrical properties of the contact are stable up to 300°C.

Magnetooptical Spectra in PtlCo and PtlFe Multilayers

K. TSUZUKIYAMA, Y . TOGAMI, M. FUJISAWA and T. FUKAZAWA, Jpn. 3. Appl. Phys., 1992, 31, (1 l),

Magnetooptical (MO) spectra were measured at 1.2-5.9 eV in Pt/Co and Pt/Fe multilayers and corresponding Pt-Co and Pt-Fe alloys which were produced by DC magnetron sputtering. Simulation of MO spectra performed by the virtual optical constant method showed that spectral behaviour of multilayers can be explained by formation of an alloy layer of thickness - 6.5 A at the interface between the Pt layer and the transition metal layer comprising the multilayers. The off-diagonal conductivities obtained suggest that magnetooptical spectra of multilayers are caused by those of corresponding alloys formed at the interface.

K. SATO, H. HONGU, H. IKEKAME, J. WATANABE,

3603-3607

Microstructures of Pt/Co Films Deposited on Sputter-Etched Underlayers

TSUNASHIMA and S. UCHIYAMA, Jpn. 3. Appl. Phys.,

k/Co multilayered films deposited on a sputter etched SiN underlayer show larger magnetic anisotropy, 1 x 10' erg/cm3, and better squareness = 1, than those on non-etched underlayers. The etching is shown to improve the multilayer structural order. The etching of underlayers transforms the Pt/Co films &om island structure to continuous structure in an early stage of film growth. SEM and STM suggest that the sputter etching flattens the surface of the underlayer.

Subpicosecond Photoinduced Switching of Second-Harmonic Generation from a Ruthenium Complex in Supported Langmuir- Blodgett Films

S. SUMI, K. TANASE, Y. TERAGAKI, K. TORAZAWA, S.

1992,31, (lo), 3328-3331

H. SAKAGUCHI, L. A. GOMEZ-JAHN, M. PRICHARD, T. L. PENNER, D. G. WHITTEN and T . NAGAMURA, 3 Phys. Chem., 1993,97, (8), 1474-1476 Ultrafast modulation of the second harmonic (SH) intensity &om a Langmuir-Blodgett film consisting of a Ru complex, Ru bipyridyl, with one of the ligands being substituted by amide groups, is shown by laser irradiation of the film at 1064 nm. The switching of the SH intensity is shown to occur in less than 2 ps by a picosecond pump-probe experiment.

Size Effect on the Electrical Conduction and Noise of Ru0,-Based Thick Film Resistors B.-S. CHIOU, J.-Y. SHEUand W.-F. WW,J Electron. Muter.,

The temperature dependence of sheet resistance for a generic Ru0,-based resistor of composition 20

12 Wt.%SiO,) was evaluated. A combined tunnevpar- allel conduction model was used to describe the resistance behaviour with respect to temperature variation. The geometry of the film, such as aspect ratio and thickness, has a significant effect on the electrical characteristic of the thick film assembly.

1992, 21, (12), 1105-1110

Wt.%R~0,-80 W.% glass (63 ~t.%Pb0-25 wt.%&O,-

MEDICAL USES Crosslinking of Adjacent Guanine Residues in an Oligonucleotide by cis- [Pt(NH,),(H,O),]z': Kinetic Analysis of the Two-step Mechanism F. GONNET, J. KOZELKA and I.-C. CHOTTARD, Angew. Chem. Int. Ed. Engl., 1992, 31, (lo), 1483-1485 A new method for determination of the four rate constants of the two-step reaction between an oligonucleotide containing a GpG unit and cis- [Pt(NH,),(H,O)JZ' has been developed. The method consists of treating known amounts of oligonucleotide with nearly stoichiometric Pt complex in aqueous solution, and periodically taking aliquots which are quenched by addition of a saturated KCl solution followed by cooling to liquid N, temperature.


NEW PATENTS METALS AND ALLOYS

Platinum-Palladium-Gold Alloy for Decorative Use CITIZEN WATCH CO. LTD .3apanese Appl. 41147,932 A Pt-Pd-Au alloy containing 85-95% Pt, 2-10% Pd, 1-5% Au and at least one of Ru, Ni, Co, Cu and 0.2-5.0% Cr in total, is used for the outer dressing of a wrist watch. The alloy has a brighter Pt colour tone, excellent machining and polishing performance, and scratch resistance.

Palladium Metal Powders NE COMECAT. K. K. Japanese Appl. 412 10,48 1 Ready mixed powder is composed of Pd or Pd alloy, containing 60% Pd of an average grain size of 50 A and includes organic Rh or In compounds as 0.005-1.0 wt.% metal. The super pulverised metal powder is dispersed in an organic solvent and made into a thin film on the substrate. The powder gives reduced delamination andor cracking of the coated layer, and is used for wiring hybrid IC devices.

CHEMICAL COMPOUNDS Preparation of Platinum Group Metal Carboxylates for Catalysts MOONEY CHEM. INC. World Appl. 92110,460A Pt group metal or Re carboxylates are prepared from a mixture of at least one alkali or alkaliie earth metal salt of a carboxylic acid, at least one Pt group metal or Re salt having a different anion and an organic liquid, by maintaining below the decomposition temperature of the components or products. A heterogeneous catalyst can be prepared by supporting the composition on a solid substrate and heating to decompose. This method provides Pt group metal and Re salts of organic carboxylic acids, useful as homogeneous catalysts, and for preparing heterogeneous catalysts, printed circuits and electrical contacts.

Iridium Composite Oxides with High Electroconductivity TOSHIBA K.K. Japanese Appl. 41130,021 Composite oxides having layered crystal structures consist of Ir; alkaline earth elements which are at least one of Ba, Ca and Sr; oxygen; and either (a) at least one of the rare earth elements including Y, (b) at least one of the alkali metals Na and K, or (c) at least one of F, C1 and Br. This method produces composite oxides containing Ir which show high metallic electroconductivity at room temperature, together with super electroconductive characteristics at low temperature.

Preparation of Tetraammine Platinum Complexes

Tetraammine Pt complexes, for example tetraammine Pt(I1) bicarbonate, can be prepared simply and effectively by adding at least one salt selected from soluble carbonates, bicarbonates and carbamates to a solution containing tetraammine Pt complex ions. The complexes can be prepared at low cost and can be used for catalysts and plating.

N.E.CHEM. CAT. K.K. 3apaneseAppl. 41169,593

ELECTROCHEMISTRY Electrochemical Detection System with Microelectrode Array US. DEPT. ENERGY US. Patent 5,120,421 An electrochemical detection system consists of a microelectrode array detector of discrete sensing elements, and an electronic means for receiving, con- verting and displaying the information. The electrodes used are preferably of Pt, Ir, Au, C, V, or a chemically modified electrode, or Ag may be used. The system is used to determine the type and concentration of elements present in testing solutions, effluents, and so on. The detector has high sensitivity, high signal:noise ratio, and may be incorporated into a hand-held system.

Rejuvenation of Electrochemical Cell Membranes or Diaphragms DOW CHEM. CO. U.S. Patent 5,133,843 A membrane or diaphragm from an electrochemical cell having a metallic coating, preferably Pt or Pt oxide, is rejuvenated by treating with an inorganic acid solution of aqua regia at 35-70°C to dissolve the metallic particles, and treating with a basic solution such as NaOH. The metallic particles, preferably Pt, can be recovered. The method is used for example to improve the performance of a chloralkali cell after a shutdown period by rejuvenating the membrane separator, and can treat for example, membranes made of ‘Nafion’.

Electrolytic Manufacture of Palladium Ammine Hydroxides AT. & T. BELL LAB. U.S. Patent 5,135,622 Pd ammine hydroxides are produced by electrolysis at up to 40°C in a cell having a Pt or Pt on Ti anode, a stainless steel or Ni cathode, a catholyte compartment containing O H ions, a product compartment initially containing Pd(NH,).” ions and anions, an anolyte compartment containing KOH, NaOH or NaSO,, and with fluorinated anion permselective membranes separating the compamnents. The process takes place at low temperature, is fast, efficient, and gives products having long shelflives containing only low amounts of the initial Pd compound.


Insoluble Electrode for Electroplating Process NIPPON STEEL cow. Japanese Appls. 41191,398-99 An insoluble electrode consists of an electrode base metal with a valve metal layer, and either (a) a 1000 A thick IrOz heat oxidised layer and a coated and baked layer of LOz, or (b) a coated and baked layer of IrO, and a 1000 A thick IrOt heat oxidised layer. Preferably the baked IrO, film is -5 pn thick and is formed by coating-drymg-baking at 450°C 6-8 times.

Platinum-Titania-Silica Catalytic Electrode T. MIYANOH Japanese Appl. 4/193,972 A semiconductor electrode for use in electrolysis is produced by moulding a homogeneous mixture of powdered SiO, powdered TiOz and Pt black, or by coating a solid material with the mixture, and then sintering the moulding or coated solid. A catalytic electrode is produced, useful for electrolytic oxidation of organic matter in solution.

Titanium Electrode Coated with Platinum and Rhodium ISHIFUKU KINZOKU KOGYO K.K.

Japanese Appl. 41210,487 A Ti(-alloy) base electrode is coated with a Pt layer, a Rh oxide layer over the Pt layer, and an oxide coating layer on the Rh oxide layer. The oxide layer comprises 80-100% Pd oxide and 0-20% Rh oxide. The Pt layer is coated with a compound solution which provides the Rh oxide upon pyrolysis and the upper oxide layer by a similar process.

ELECTRODEPOSITION AND SURFACE COATINGS Palladium Coated Vacuum Cylinder for Molecular Beam Epitaxial Units NEC cow. Japanese Appl. 41173,962 The inside surface of a vacuum cylinder used for molecular beam epitaxial units and surface analysis and measurement units is coated with Pd. In an example a vacuum cylinder was evacuated and Pd vapour induced to deposit Pd f im on 95% of the total inside surface area. The process reduces the amount of con- taminant molecules present.

APPARATUS AND TECHNIQUE Hydrogen Getter for Cryogenic Vacuum Tube SAES GETTERS S.P.A. European Appl. 496,711A A getter for removing H, from a vacuum environment at cryogenic temperatures consists of a 25-1000 pm thick Al strip support coated on one or both faces with particulate ALO,, and then coated with Pd oxide at a wt. ratio of 99.9:O.l to 5050, or having Pd oxide present as multiple clusters. The getter functions by oxidising H, to H20 which is directly absorbed by the AIz0, and the PdO without passing through the vapour phase, and the absorption is not limited by the surface area of the getter.

High Surface Area Platinum Recovery System

A Pt recovery system for a nitric acid plant consists of a foraminate element of Pd or a Pd alloy containing a minor amount of another Pt group metal, Au, Mn, Cr, B, Cu or others. The Pd alloy element is con- tacted with the effluent stream to recover Pt and Rh lost from a Pt-containing catalyst by volatilisation during NH, oxidation above 850°C. Average linear velocity across the Pd alloy element is reduced, and the Pd alloy wt. and surface area per unit cross-sec- tional area is increased, raising collection efficiency.

Proximity Sensor for Detecting Rotary Machine Vibrations BENTLY NEVADA COW. US. Patent 5,126,664 A proximity sensor has a coil for detecting rotating machinery which consists of an alloy of 89 wt.% Ag and 11 wt.% Pd, and is provided with a number of turns, for example 132, to give the desired inductance to operate at a radio frequency of 1 MHz. The effective inductance and resistance of the coil are affected by the rotating machinery which propor- tionately changes the amplitude of the oscillator signal. The coil is suitable for small diameter use, and has relatively low temperature errors - less than 10% over a wide temperature range of operation.

Platinum Laminate Electrode for Use in Sensors NOK COW. Japanese Appl. 41128,646 A laminate electrode for a sensor consists of Pt laminated on a high melting point metal such as Cr, Ti, Ta, Zr or Nb. The new laminate electrode, especially Pt-Cr or Pt-Nb, has high environmental resistance, that is, it shows little resistance change under high temperature and high humidity conditions.

Method for Analysing the Platinum Component of Car Exhaust Catalysts TOY0 KOGYO CO. Japanese Appl. 411 38,362 A method for analysing the Pt component of car exhaust purification catalysts involves immersing in a solution of mineral acid to dissolve components other than Pt, separating the Pt component h m the canier in the mineral acid solution without ionisation, separating the Pt component from the mineral acid, and analysing by XRD.

Carbon Monoxide Gas Sensor Having Iron- Palladium Alloy Wire Coils

JOHNSONMATTHEY MC. U.S. Parent 5,122,185

DENKI JIIU ZAIRYO KENKYUSHO Japanese Appl. 41140,656

A CO gas sensor for catalytic combustion uses has an active part and a compensation part positioned in series and made from coils of Fe-Pd alloy wire containing 15-60 wt.% Fe and 40-85 wt.% Pd, or Fe-Pd- Co wire. The coils have improved uniformity and mass-producibility. The sensor temperature is preferably < 200"C, and shows higher CO sensitivity.


Platinum-Rhodium Alloy Crucible for Growing Manganese-Zinc Ferrite Single crystals SHINETSU CHEM. lND. CO. LTD.

Japanese Appl. 41154,697 A crucible of Pt or Pt-Rh alloy is used to grow a Mn- Zn femte single crystal with S 500 ppm contamination of Pt and/or Rh by maintaining the whole raw material in the completely melted state for one hour or more before starting crystal growth, and with optional simultaneous ZnO sublimation. Using this method a high quality Mn-Zn ferrite single crystal of low Pt contamination.

Surface Treating Liquid for Dirt Detection on Insulating Substrates TOPPAN PRINTING co. LTD. Japanese Appl. 41174,355 A surface treating liquid consists of Pd chloride dissolved in an acid solution with the pH controlled to be not less than 4 by an alkali solution, and preferably includes tartrates, pyrophosphates and citrates. The solution is used to detect the dirty parts of an insulating substrate which have previously been difficult to detect. On contacting the liquid with the substrate the Pd acts as a catalyst to deposit metal by an electroless plating process, thereby detecting the dirty part of the substrate.

HETEROGENEOUS CATALYSIS Platinum Group Metal Catalyst for Hydrogen Peroxide Production MITSUBISHI GAS CHFiM. CO. INC.

European Appl. 498,l 66A H202 is produced with high efficiency by reacting H, and 0, at 0-50°C and 3-1 50 wan' in water or an aqueous solution containing a H,02 stabiliser, in the presence of a Pt group metal catalyst consisting of (a) Pt or Pd supported on a carrier such as a micro- porous resin, absorbed on which is a water-insoluble organic halogen compound, or (b) Pt or Pd supported on a carrier with such a compound already absorbed. The absence of halogen ions in the reaction medium reduces dissolution of the catalyst and corrosion of the reaction vessel, and makes their removal from the product unnecessary.

Platinum Catalyst for Preparation of Pyrocatechol Compounds BASF A.G. European Appl. 499,055A F'yrocatechol monoethers or pyrocatechols are prepared by reacting a 2-hydroxycyclohexanonedialkyl metal in the presence of a partially deactivated Pt metal catalyst in the gas phase or in the presence of water. The urocess is simpler and more economical

Semiconductor Gas Sensitive Device with Platinum-Platinum Black Electrode Layer OKU SEISAKUSHO CO. LTD. Japanese Appl. 41175,653 A semiconductor gas sensitive device used to sense 0, and ozone gases at ordinary temperatures has an electrode layer of Pt and Pt black formed on the insu-

than P r ~ o ~ s processes --it does not produce hydro- quinone, and does not require high temperatures or a large amount of alkylating agent. The products are used as intermediates in the preparation of phanna- ceuticals such as verapd, perfumes and f l a v o d P such as vanillin.

lating layer of the gate part of a field effect transis- tor, and a ceramic layer bonded to the electrode layer using resin. The resin increases the mechanical strength and adhesion of the ceramic layer.

Oxygen Partial Preasure Measurement Sensor for Molten Salt NIPPON STEELCOW. Japanese Appl. 4/181,155 A sensor consists of a protection tube made of 3-9 mol % CaO and/or 5-12 mol % of Y203, and the rest of Zr02, with a Pt powder filling the protection tube, a Pt electrode dipped in the Pt powder, and a Pt electrode dipped in a molten salt outside of the tube. Both Pt electrodes are electrically connected to measure the potential difference between them.

JOINING Stress-Relaxed Ceramic-Metallic Joint NIPPON CEMENT ILK. Japanese Appl. 41164,837 A ceramic and metallic member are joined by incor- porating 2 mm or more of Pt, Rh and/or an alloy between them and then soldering together using a metallic or oxide solder having a melting point as high as 1083°C or over. The Pt, Rh or alloy acts as a stress- relaxation layer and provides a joint for use in an oxidative atmosphere at temperatures over 700°C.

Iridium-Alumina Catalyst for Hydrazine Decomposition AGENCY OF IND. SCI. & TECHNOLOGY

European Appl. 499,264A A catalyst for hydrazine decomposition is prepared by impregnating A120, with a solution of Ir chloride in ethyl alcohol, and then drying and firing to give 5-30 wt.% Iron the catalyst. The catalyst is used for decomposition of hydrazine in a gas turbine or a thruster for altitude control of an artificial satellite, and has higher activity which is lost less readily.

Low Platinum Content Catalyst for Conversion of Aromatic Fractions LEUNA-WFlRKFl A.G. European Appl. 499,799A A catalyst for conversion of industrial C8 aromatic fractions in the presence of H, and basic N compounds consists of zeolite crystals covered with 1-5 wt.% A l z o 3 and an A120, ma& containing 0.014.1 wt.% Pt, with a preferred zeolite content of 10-70 wt.%. The catalyst is used for aromatic hctions containing xylenes and up to 30 wt.% ethylbenzene, and isomerises the xylenes to an equilibrium value while dealkylating or isomerising the ethylbenzene. The catalyst contains only one tenth of the Pt in prior art catalysts, is highly selective, and with high activity.

Platinum Met& Rev., 1993,37, (2) 121

Ruthenium and/or Palladium Hydrogenation Catalysts BAYER A.G. European Appl. 501,265A Hydrogenation catalysts consist of 0.05-5 wt.% Ru, Pd or a mixture of these in 1:9 to 9:l wt. ratio on a carrier containing niobic acid, tantalic acid or a mixture of these. The catalysts are especially useful for synthesis of cyclohexylamine and dicyclohexylamine compounds by catalytic hydrogenation of the corresponding aniline compounds, and give the products in chosen ratios, higher yields, and have longer useful life than known catalysts.

Palladium Catalysts in Pentafluoroethane Production ELF ATOCHEM. S.A. European Appl. 506,525A CF,.CF,H was produced by hydrogenolysis in the vapour phase of CF,.CF,CI using a 0.1-5 wt.% Pd catalyst supported on ALO,, fluorinated A20, or AL03 fluoride carrier, at 200-350°C, a H,:CF,.CF,H = 1-2, and H, pressure of 1-50 bar. The carrier was impregnated with an aqueous or organic solution of a Pd derivative. Using this Pd catalyst, the product is obtained with a very high selectivity.

Catalyst for Oxidising Organic Contaminants in Water UNITED TECHNOLOGIES CORP

Pretreated Noble Metal Catalyst for Naphtha Reforming EXXON RES. & ENG. CO. U.S. Patent 5,137,620 A catalytic reforming process involves contacting a naphtha feed at 750-980°C and 5-25 atm with a noble metal reforming catalyst comprising Pt, Pt-Rh, Pt-Ir, Pt-Re, Pt-Sn, Pt-Rh-Ir, Pt-Ir-Re, Pt-Ir-Sn, Pt- Re-Sn or Pd on a support selected from silica, ALO,, SiOz-A120,, Sn modified ALO, or zeolite. Treatment of the catalyst with an unsaturated aliphatic hydrocarbon at 250-550°C lowers its hydrogenolysis activity during the initial stages of reforming; thus reducing the amount of undesirable gaseous hydrocarbons produced and alleviating temperature runaway.

Hydrogenation of Hydrocarbon with Palladium and Platinum Catalysts Supported on Zeolite Y of Specified Sodium Content AMOCO CORP. U.S. Patent 5,147,526 A hydrocarbon feedstock of material distillates boiling between 150-170°C is hydrogenated by reaction with H, in the presence of a catalyst comprising (a) 0.1-2.0 wt.% Pd, (b) 0.1-2.0 wt.% Pt, and (c) zeolite Y support which contains 1.5-8.0 wt.% Na. The zeolite is generally 40-85 wt.% of the support, which also contains a refractory inorganic oxide, such as AL03 or SiO,. The zeolite has Si:AI atomic ratio of 3-1 0, and Pd:Pt weight ratio of 3: 1-1 : 1.

World Appl. 92/13,805A A catalyst for oxidising aqueous organic contaminants consists of 5-20 wt.% of Pt, Pd, Ir or Ru crystallites, 100 A or smaller in size, deposited on a high surface area catalyst support such as A1201, MgO, ZrO,, SiO, or activated C. The catalyst can be used in a catalyst bed to treat a reactor feed sueam. The catalyst is used for complete removal of low concentrations of low molecular weight organic contaminants from water streams with a short residence time, low reaction temperature, and a low reaction pressure.

Noble Metal Catalyst for Preparation of Cyclohexeny'p~idine KOEI CHEM. m. CO. L m . Japanese 4/169372 2,3-Cyclohexenylpyridine is prepared by isomerisation of 1,2,3,4-tetrahydroq~inoline at 2O0-25O0C, for 1-7 h, in a N, atmosphere, in the presence of 1-50 wt.% of Pd, Rh or Ru. Using this starting material the product is obtained in high yield and with high purity, and can be used as an intermediate for pharmaceuticals and agrochemicals.

Ruthenium-Zeolite Hydrorefining Catalysts ELF FXANCE World Appl. 92/15,399A A hydrorefining RuS/zeolite catalyst is prepared, and is used for HC charges, particularly in hydrodenitre genation processes. The Ru-containing catalyst, which is used either alone, or in combination with catalysts of AlzO, containing Ni, Mo, W or Co, gives improved performance in desulphurisation, and particularly in hydrodenitrogenation reactions where the reaction is not inhibited by the presence of quino- lines which reduce the denitrogenation yield.

Rhodium-Ruthenium Catalyst Composition for Preparation ofJ-Hydroxyesters EASTMAN CHEM. CO. U.S. Patent 5,135,901 A novel catalyst composition consists of a Rh component which may be a salt or a complex, a Ru component present at 0.001-1000 times the molar concentration of the Rh, and as promoter a compound containing N, P, As or Sb present at 0.1-100 times the molar concentration of the Rh.

Catalyst Composition for Purification of Automobile Exhaust Gases KAWASAKI STEEL COW. Japanese Appl. 4/176,357 A catalyst composition used for the purification of exhaust gases from automobile engines consists of a high silica zeolite ion-exchanged with at least one of Pt, Pd, Rh, Ir and Ru, and a heat resistant oxide containing at least one of Pt, Pd, Rh, Ir and Ru, optionally supported on a monolith support. The catalyst has good activity and durability.

Platinum-Ceria-Alumina Catalyst for Exhaust Gas Purification

An internal combustion engine exhaust gas purification catalyst is prepared by impregnating highly active CeO, powder of surface area > 100 m'/g with a solution containing Pt compounds, heating to form a CeO,/Pt group metal catalyst powder, mixing with active ALO, powder to form a slurry, coating a catalyst carrier, and impregnating with Pt group metals.

KYAT- KOGYO K.K. Japanese ApPl. 41180,835

Platinum Me& Rev., 1993, 31, (2) 122

Three-Way Catalyst with Ceria-Platinum Group Metal Component

A catalyst for purification of internal combustion engine exhaust gases is prepared by impregnating highly active CeO, powder of > 100 m'lg surface area with Pt p u p metal compounds, heating, mixing with active Al,O, powder to form a slurry, using to coat a catalyst carrier base material, and impregnating with Pt group metals.

Platinum-Carbon Catalyst for Amino- Fluorophenol Production SUMITOMO CHEM. co. LTD. Japanese AppI. 41182,456 4-Amino-3-fluorophenol is produced by catalytic reduction of o-fluoronitrobenzene with 5% PdC in the presence of a S compound and a surfactant (such as quaternary ammonium halides), usually 5-20 wt.% of HSO. and dodecyl trimethyl ammonium chloride, at 0-200°C for 2-50 h. The obtained compound is isolated and purified by conventional methods. The product is produced in a high yield, for example 94.3 % yield, and is used as an agricultural intermediate.

Platinum-Zeolite Three-Way Catalyst for Car Exhaust Purification TOSOH COW. Japanese Appl. 411 87,244 A three-way catalyst for car exhaust purification consists of a durable support such as a cordierite mono- lithic support, a coating layer containing zeolite powders treated to remove Al from their surfaces, and Pt loaded on the zeolite layer by ion-exchange. The Pt is hardly aggregated even after high temperature operation for a long time. The catalyst is used to remove hydrocarbons, CO and NO. from car exhaust, and can remove NO. with higher efficiency above 600°C.

Noble Metal-Silicate Catalysts for Decomposition of Nitrogen Oxides TOYOTA JIDOSHA K.K. Japanese Appk. 41193,34647 NO. decomposition catalysts consist of at least one of Pt, Pd, Rh, Co and Cu camed on a crystalline Fe silicate or a crystalline Ga silicate. The catalysts are used for decomposing NO. in the exhaust gas of chemical processes, such as nimc acid production plants, can remove NO,, hydrocarbons and CO simultaneously from automobile exhaust gas, and can be run after exposure to high temperatures.

Palladium Catalysed Preparation of Substituted Aromatic Carboxylic Acid Esters UBE IND. LTD. Japanese Appk. 41193,847-49 Substituted aromatic carboxylic acid esters such as hydroxybenzoates are prepared by reaction at 50-2OOOC and 0.1-5 kg/cm' pressure of substituted aromatic bromides, alcohols and CO, in the presence of 0 . 0 5 5 wt.% of a Pd catalyst (compared to the bromides) and either amine compounds or inorganic bases. In examples the catalysts used were 10% P d C black and Pd(Ac),. By this method the esters can be produced in good yields under mild conditions.

KYATARA KOGYO K.K. Japanese AHZ. 41180,835

Three-Stage Combustion Catalyst System KOBE STEEL LTD. Japanese Awl. 41197,443 A combustion catalyst system consists of a series of combustion catalysts with the fiont stage catalyst containing Pt andor Pd, the middle stage catalyst consisting of a substituted layer aluminate combustion catalyst with Pt andor Pd added, and a new rear stage substituted layer aluminate combustion catalyst. Alternatively the front and middle stage catalysts may be the same as the middle stage catalyst in the arrangement above. These systems contain both a combustion catalyst exhibiting good ignitability at low temperatures and a combustion catalyst exhibiting high activity at high temperatures.

Ruthenium Catalysed Preparation of Chlorotrifluoroeth ylene NPPON W O N K.K. Japanese Appl. 41202,147 Chlorotrifluoroethylene is prepared by reaction of 1,1,2-trichloro-1,2,2-trifluoroethane with H, at 15&4OO0C, for 1-4 h, in the presence of a catalyst consisting of 0.1-5 wt.% Ru and 0.1-5 wt.% of at least one of Au, Ag, Cu, Te, Tl, Bi and As supported on active C. The high activity of the catalyst gives a high yield of the product (52-90%) in the gas phase without formation of side products, by a one-step reaction. The product can be used as a monomer for functional fluorinated polymers, or as an intermediate for physically active compounds.

Platinum-Lead Catalyst for Preparation of Furan-Dicarboxylic Acid FURCHIM S.R.L. French Appl. 2,669,634 Preparation of 2,5-furan-dicarboxylic acid is effea- ed by oxidation of hydroxymethyl fdu ra l in an aqueous alkaline medium, in a current of 0 , and using a catalyst consisting of W3% Pt and Pb as activator on an activated charcoal support of > 1000 m2/g surface area, with a 0 .61.5 wt. ratio of Pb:Pt. The new catalyst can be recycled 8-1 5 times, gves improved selectivity and conversion, shorter reaction times, no secondary by-products, the Pt consumption rate is reduced and irreversible poisoning is avoided by Pb activation. The product is an important base monomer used to prepare polymers with improved mechanical properties.

Palladium-Alumina Dehydrogenation Catalyst ARZNEMllTELWERK DRESDEN G.m.b.H.

East German Patent 298,744 Dehydrogenation of 1,2-diphenylethanes to the corresponding diphenylethenes is effected in the liquid phase, and in the presence of a H acceptor and a catalyst consisting of 1-8 wt.% Pd uniformly distributed throughout a moulded carrier which consists of active Al,O, modified with 2-5 wt.% of an alkaline earth metal oxide. The catalyst can be prepared by a simple process, is easily regenerated, and can be used in the chemical and pharmaceutical industries.


HOMOGENEOUS CATALYSIS Platinum Complex Catalysts for Hydrosilation Reactions MINNESOTA MINING & MFG. CO.

WorldAppL. 92110,529A and 92/10,543A An actinic radiation-activated hydrosilation reaction between an unsaturated aliphatic compound and 0.1-10 wt. equivalents of a compound containing Si- H bonds is effected in the presence of 5-1000 ppm of a Pt catalyst, 50-50,000 ppm of a free-radical pho- toinitiator able to absorb actinic radiation and accel- erate the reaction, and optionally 50-50,000 ppm of a sensitiser. The Pt catalyst is an (q5-cyclopentadi- enyl)m(o-aliphatic) Pt complex or an (q-diolefin)(a- aryl) Pt complex. The process can be used to produce low molecular weight Si compounds and to cure polymers, and the composition may be used for dental impressions or release liners.

New Organosilicon Compounds for UV- Curable Coatings DOW CORNING COW. U.S. Patent 5,136,065 A new organosilicon compound is selected from certain silanes or organosiloxanes prepared by the reaction of a propargylester with either a uiorganohy- drogensilane or an organohydrogensiloxane in the presence of a Pt-containing hydrosilylation catalyst. The Pt catalysed hydrosilylation reaction of the organohydrogensiloxane occurs exclusively at the propargyl group leading to high product yield. Solutions of organosiloxanes are used for UV-curable coatings and W absorbers as they form an insoluble crosslinked material when UV irradiated.

Rhodium Catalyst Recovery during Hydroformylation Process EASTMAN KODAK CO. U.S. Patent 5,138,101 A low temperature hydroformylation process uses a catalyst of Rh and an organophosphine compound and results in a product solution containing a high- boiling aldehyde, the catalyst components and a hydroformylation solvent. The aldehyde product is recovered by contacting the product solution with a primary alkanol-H,O extraction solution to form a 2- phase mixture, and separating the catalyst and product containing phases. Recovery does not result in significant loss of catalyst components.

Palladium Complex Catalyst for Preparation of Cyanobiphenyl Derivatives AGENCY OF IND. SCI. & TECHNOLOGY

Japanese Appl. 41169,564 A thermally stable cyanobiphenyl is prepared by reaction of a halogenated biphenyl with a cyanide in the presence of a Pd complex catalyst and a crown ether. The catalyst preferably consists of a Pd compound, such as PdCl,, and a phosphine, such as an aromatic phosphine, alkylphosphine or diphosphine. Cyanobiphenyl is prepared efficiently by this method.

Catalytic Production of Branched Fats from Maleic Anhydride HENKEL KGM. German Appl. 4,102,500 Branched fats are produced by addition of maleic anhydride to unsaturated fatty acids, preferably oleic acid, or their lower alkyl esters, preferably methyl oleate, at 90-175OC, in the presence of Rh and/or Pt catalyst(s) present at 0.005-10 wt.% with respect to maleic anhydride. The catalyst(s) give high product yields, at low temperatures if Rh salts are used.

FUEL CELLS Platinum Alloy Electrocatalyst for Fuel Cell Anode STONEHART ASSOC. INC. European &I. 501,930A An electrocatalyst consists of an alloy of 10-39 at.% Pt, 30-5 at.% Ni, 30-5 at.% Co and 30-3 at.% Mn, preferably 39 at.% Pt, 26 at.% Ni, 26 at.% Co and 9 at.% Mn, on a porous inorganic oxide support such as ALO, or SiO,, or C. The catalyst has excellent poisoning resistance with respect to CO and is especially useful for the anode of a fuel cell employing liquid natural gas as the anode gas.

New Platinum Alloy Catalysts for Phosphoric Acid Fuel Cells STONEHART ASSOC. INC. Japanese Appl. 41141,236 A new catalyst for use as a phosphoric acid fuel cell electrode consists of a C support loaded with a Pt alloy containing Au, Au and Ni, Co or Mn, with a Au content of 3-20 at.% with respect to the Pt. The catalyst is prepared by reducing Pt and Au compounds to deposit Pt and Au on the C support, adding an organic acid amine salt of Ni, Co or Mn, then heating to form the Pt alloy.

Catalytic Removal of Carbon Monoxide from the Fuel Gas for a Fuel Cell CANADA MIN. NAT. DEFENCE

Canadiun Patent 1,305,212 A low temperature acid fuel cell with a noble metal anode and a solid polymer electrolyte can be operated with a fuel gas containing CO by first reacting the CO with an 0, containing gas at 10-16°C and a pressure of 500 psig, in a column containing a catalyst of 0.01-5 wt.% Pt, Rh or Ru on a support of Al,O,, SiO,, or others. The CO is converted to C02 giving a fuel gas containing only 2-10 ppm CO.

Fuel Cell Electrodes Containing Platinum CANADA MIN. NAT. DEFENCE

Canadiun Patent 2,052,221 A composite electrode for use in a fuel cell consists of a conductive sheet material, preferably C fibre paper, impregnated with 2-14 wt.% of a hydrophobic polymer, preferably PTFE, deposited on which is a catalytic material of Pt and a PTFE binder. Membrane electrodes can be constructed with thin membranes to obtain maximum cell efficiency.

Platinum MetaL Rev., 1993, 37, (2) 124

CORROSION PROTECTION Corrosion Reduction Using Platinum Group Metals GENERAL ELECTRIC CO. U.S. Patent 5,135,709 Reduction of the corrosion potential of steels, stainless steel, Ni- or Co-based alloy exposed to high temperature H,O is achieved by providing a catalytic layer of a platinum group metal on the component. The coating of platinum group metal catalyses the reduction of the oxidising species and thus the amount of added reducing species needed to lower the corrosion potential of the component below a uitical potential. The method is useful for reducing corrosion of components exposed to high temperature H,O at -150°C or above, steam or condensates, for example in H,O deaerators, nuclear reactors and steam-driven central power generators.

Corrosion Resistant Material MrrSuBISHI HEAVY IND. c o . LTD.

Japanese Appl. 41187,749 Corrosion resistance material which is used for an ultrasonic wave oscillator plate for pickling, consists of Ti-6Al-4V-Pd alloy including 0.01-0.17% Fe and 0.0142% Pd, and is hot-rolled at 950-9OO0C, heated to 9O0-96O0C, H,O-cooled, heated to 540-6OO0C, and air-cooled. A strip running constantly through the pickling liquid is bolt-tightened to the oscillator plate on the body of the oscillator attached to an amplifier.

Corrosion Resistant Iron Composition for Use in Acidic Media MAGN. MINING METAL INsT.Russian Patent 1,663,041 An Fe composition with increased corrosion resistance for use in acidic media contains 1.6-2.8 wt.% C, 1.5-2.5 wt.% Si, 0.5-1.0 wt.% Mn, 18-35 wt.% Cry 0.1-0.3 wt.% Ti, 0.15-0.7 wt.% Rh and balance Fe. Corrosion is reduced by Rh atoms accumulating on the surface of the Fe in the form of 0.05-0.1 pn discrete inclusions. The Fe composition is used for pumps and retorts.

Amorphous Soft Magnetic Material for Recording Equipment sow cow. World Appl. 92/9,09 1A An amorphous soft magnetic material contains Co, Zr, Pd, and Nb, Cry V, Ta, W or Mo, and is preferably produced by quick-cooling a liquid or by a sputtering method. The material has a high saturation magnetic flux density, low coercive force, high permeability, and good corrosion and abrasion resistance.

Oxide Superconductor with a High Critical Current Density HOKURMU ELECTRIC POWER CO.

WorId Appl. 92117,407 An oxide superconductor comprises a LnBa,Cu,O, crystal (where In is at least one of Y, Sm, Eu, Gd, Ho, Er and Yb) in which Ln,BaCuO,, and a Pt, Ba and Cu composite oxide of mean particulate diameter of 1-10 pn, are finely dispersed. The superconductor produced by mixing composite oxides of Ln powders, melting, cooling, and pulverising the cooled solid, followed by addition of Pt powder and moulding.

Magneto-Optical Information Storage Medium Having Palladium Substrate U S . DEPT. ENERGY US. Patent 5,116,693 A magneto-optical information storage medium consists of a Pd substrate with an epitaxially deposited ultrathin Fe film, which has an easy axis of magnetisation perpendicular to the plane of the Fe film. This provides a medium for data storage which is magnetically stable, non-volatile, has high density, high signal to noise ratio and is erasable, and uses an ultrathin film of magnetic material to maintain vertical magnetisation of the medium.

Thick Film Resistor Paste Composition E. I. DU PONT DE NEMOURS & CO.

U.S. Patent 5,122,302 A thick film resistor paste having an admixture of finely divided particles consists of a conductive paste containing at least one Pt group metal oxide having a positive temperature coefficient of resistance and Co ruthenate; an inorganic binder; and a filler; all disDersed in an organic medium. The Daste is used - especially for temperature sensor applications, but also for gas or liquid flow sensors, surge suppressors ELECTRICAL AND ELECTRONIC

ENGINEERING or liquid level indicators.

Rare Earth Oxide Superconductor INT. SUPERCONDUCTIVITY TECHNOLOGY CENT.

European Appl. 493,007A A superconductor consists of oxide grains containing Y, Gd, Dy, Ho, Er or Yb; Ba; Cu; and 0.01-5 wt.% Rh andor Pt contained in the grains. The superconductor is prepared by mixing powders of the rare earth metal, Ba and Cu with Rh and/or Pt (compound), shaping, heat treating, slow cooling, and heat treating at 6504OO0C for 10-50 h in 0,. The material exhibits a very high pinning effect and an excellent critical current density in a high magnetic field.

Fabrication of a Bismuth-Based Superconducting Material Using Platinum wires UNIV. LELAND STANFORDJUNIOR

U.S. Patent 5,122,504 A ribbon of Bi-based superconducting material is fabricated by placing two parallel Pt wires along the sides of a Bi2Sr2CaCuZO1 source material, melting the top so that a liquid film is created, pulling the wires in a vertical direction to cool the melted material so that it solidifies to form a solid ribbon of superconducting material, and preferably annealing in air.

Pkatinum Metals R e v . , 1993,31, (2) 125

Antiferromagnetic Thin Layer with Improved Corrosion Resistance HITACHI LTD. Japanese Appl. 41162,207 An antiferromagnetic thin layer consisting of an Fe- Mn-Ir alloy gives a diamagnetic thin layer having a high bias magnetic field and improved corrosion resistance. When Pt, Rh or Ru is added to Fe-Mn-Ir the corrosion resistance and magnetic field are further improved. The antiferromagnetic thin layer can be used for a magnetic resistance effect element.

Photomagnetic Recording Medium with Cobalt and Platinum Layers SONY cow. Japanese Appl. 411 67,406 A photomagnetic recording medium consists of a recording layer having alternately laminated artificial lattice magnetic films consisting of Co and Pt layers, with the artificial lattice magnetic films multilayered through transparent dielectric layers. The photomagnetic recording medium has good thickness and a good rectangular-loop ratio, and is used for recording and play-back of information.

Bismuth System Superconducting Material Containing Platinum Fine Powder SUMITOMO ELECTRIC co. Japanese Appl. 41170,321

Electrically Conductive Metal Powders for Multilayer Ceramic Capacitors E.1 DU PONT DE NEMOURS & CO

U.S. Paten2 5,126,915 Electrically conductive metal powders consist of finely divided particles of Pt, Pd, Au, Ag, Cu, Ni, mixtum and alloys of these with a coating of a refractory metal oxide which is insoluble in the elecnoconductive metal and non-reducing in its presence, for example hydrous Al,O, or an oxide of Mn, Ti or Pb. The electroconductive metal is preferably Pd, Ag or a Pd-Ag alloy. The metal powders are claimed for use in the manufacture of multilayer ceramic capacitors.

Deposition of Platinum Catalyst Patterns for Printed Circuit Board Manufacture GENERALMOTORSCOW. U.S. Putenr 5,139,818 A method for applying catalytically active metal clusters to a ceramic substrate, particularly ALO, involves depositing a film of solution containing tris(l,2- diaminopropane)Pt(IV) 2-ethylhexanoate in xylene onto the substrate, selectively irradiating, rinsing with xylene to remove the soluble Pt compound, and pymlysing in the presence of 0, at 300-10OO0C for up to 5 min. The catalytically active metal clusters catal- yse localised electroless deposition of Cu, (or Pd-Sn).

Photomagnetic Recording hYer Containing Noble Metal Layers

Japanere A@1. 41132y030

A Bi system superconducting material is based on Bi or (Bi,Pb)-Sr-Ca-Cu, added to which is 0.05-0.4 wt.% of fine Pt powder of average grain diameter up to 2 um. The material is also used in the production HITACHI LTD.

A photomagnetic recording layer is composed of reciprocal layers of noble metal and transition metal alloy where the noble metal layer is Pt, Pd, Rh or Au, and the other layer is mainly Fe or Co containing Pt, Pd, Rh, Au, Nb, Ti, Ta or Cr. In an example layers of Co,Nb, and Pt were reciprocally laminated on a plastic substrate by Sputtering. The recording layer has enhanced vertical magnetic anisotropy, reduced saturated magnetisation, enhanced coercivity, and improved recording fidelity.

Improved Life Magneto-Optical Recording Medium DAICEL CHEM. m. LTD. Japanese Appl. 41137,238 A magneto-optical recording medium with improved running life has a recording layer consisting of a reciprocal laminated Pd-Co group artificial lattice film andor a reciprocal laminated Pt-Co artificial lattice film on a transparent substrate.

Improved Quality Photomagnetic Recording Medium SEIKO EPSON COW. Japanese Appl. 41143,947 A photomagnetic recording medium consists of a s u b suate and a recording layer composed of alloy layers containing at least one of Gd, Tb and Dy, and at least one of Pt, Pd and Co; preferably PtGdCo alloys containing 5-60 at.% Gd are used. The saturated magnetisation of the recording layer can be reduced, and thus the quality of the photomagnetic recording medium is improved.

of superconducting line which involves coating this material with a metal coating material, and then effect- ing plastic treatment and thermal treatment at least once. The material and superconducting line have high critical current density and critical current.

Composition Containing Ruthenium for Use in Thick Film Resistors SUMITOMO METAL MINING CO.

Japanese Appl. 41181,701 A composition for use in a thick film resistor consists of a Ru compound conductive powder containing Ru; Ba; Sr, Ca, La, Ce, Pr or others; Zr, Ti, Hf, Nb or Ta; and 0, together with a non-reducing glass !?it and a vehicle. The Ru conductive powder is present at 15-75 wt.% of the powder and glass tiit. The composition is stable in a non-oxidising atmosphere, has a good temperature coefficient of resistance, and is used in a thick film resistor for a hybrid IC circuit or chip resistor, and may be used with Cu conductors.

Baseplate for a Thin Film Device NEC cow. Japanese Appl. 41182,393 A baseplate for a functional thin film device consists of a ferroelectric epitaxial film formed over an epitaxial electroconductive oxide film of IrOz, OsOz, RuO, or ReO,, on a monocrystalline Si baseplate. This structure, where the electroconductive oxide film has a refractive index lower than that of the ferroelectric film, provides a light waveguide, permit- ting its use as an optical switch.


Photomagnetic Recording Medium HITACHI LTD. Japanese Appl. 41186,545 The structure of over-writable photomagnetic recording medium for high density recording consists of two layers of merent magnetically bound characters. One layer is made of an alloy based on at least one of Dy, Tb, Ho or Gd, and at least one of Fe or Co. The other layer is a reciprocal laminate of at least one platinum group metal of Pt, Pd or Rh, and at least one of Fe or Co. It can be written-read or erased by a laser beam, and it has an improved corrosion resistance.

Opto-Magnetic Recording Films HITACHI LTD. Japanese Appl. 41186,706-7 A 6lm structure for opto-magnetic recording consists of a laminated film layer containing Pt, Pd, Rh and Au, and a layer based on Fe, Ni and Co with other elements; the layers above are laminated in turn to make a multilayered structure. The rare earth elements in the ferromagnetic layer and the alloy layer based on Fe group elements may provide a dominant sub-lattice magnetisation. This allows more stable storage of the written information.

Platinum or Palladium Multiplex Optical Magnetic Storage Device S E X 0 EPSON COW. Japanese Appl. 411 86,708 A multiplex optical magnetic storage device consists of four successively applied layers: (1) a Co base layer, (2) and (4) layers containing a platinum group metal, preferably Pt andor Pd, and (3) a layer made of a rare earth metal with at least one of Gd, T b and Dy. The four layers can be repeatedly applied on glass, plastics or crystal by vacuum vapour deposition, sputtering or molecular beam epitaxy, to form a highly multiplexed board.

Palladium Containing Conductor Paste for Variable Resistor Electrode TANAKA MASSEI K.K. Japanese Appl. 41192,208 The conductor paste comprises Ag- or Pd-powders, in ratio 79:21-91:9, respectively, in an inorganic binder and dispersed in an organic vehicle, the binder comprises a mixture of Bi oxide and glass frit. The prepared paste can be printed on a ceramic substrate of 96% A120,, then sintered twice at 850T for 10 min, to make a conductive film of 8-12 A thick. The conductor paste is used for forming electrodes for a thick film variable resistor.

Improved Smoothness Oxide Superconducting Thin Membrane SUMITOMO ELECTRIC CO. Japanese Appl, 41193,702 A superconducting membrane consists of superconducting oxide layers and noble metal layers laminated alternately on a substrate, with the layer contacting the substrate and the uppermost layer consisting of the superconductor oxide. The oxide superconducting membrane has improved smoothness, improved superconducting characteristics, and is used for superconducting electronic devices.

Resistor Film Production for Hybrid IC FUJI XEROX co. LTD. Japanese Appls. 41279,002-3

and 41279,005 A resistor film forming material contains (a) an organic Ir compound, and (b) a compound of at least one additional element (M) selected from Si, Bi, Pb, Sn, Al, B, Ti, Zr, C or Ba, with atomic ratio MIr = 2.5-7. The compounds (a) and (b) can be carboxylate complexes, diketone type chelate, alkoxide or mercaptide compounds of Ir or M. The chosen solvent for the film forming material can dissolve metal or non-metallic organic compounds. Resistor film for hybrid IC and thermal heads contains particles of up to 100 A diameter of a platinum group metal oxide, and (b). The resistor film has a uniform resistance value.

TEMPERATURE MEASUREMENT Cryogenic Temperature Measurement Apparatus TOSHIBA K. K. European Appl. 510,880 A cryogenic temperature apparatus uses two circuits with Pt and C glass resistance sensors in cryogenic temperature cooling cryostats connected to a common analogue to digital converter and a CPU for processing for output. The first circuit is to measure 30&30 K and second for 304 K. Each circuit has a constant current source supplying DC current to a cryogenic temperature cooling cryostat to generate a voltage, which is amplified to a specified signal level.

Improved Temperature Sensor with High Flexural Strength

The sensor consists of an insulating base plate, covered by a Pt film. The ZrO, base plate 0.15-0.3 mm thick is covered by SiO, or A120, layers, preferable 100&5000 A thick. The Pt film of thickness 1-2 pm is produced by printing, sputtering and deposition. The adhesion of the Pt film and the insulating base plate is greatly improved. The flexural strength and temperature coefficient of resistance are high.

MURATA MFG. CO. LTD. Japanese AppI. 41265,828

MEDICAL USES New trans-Platinum (IV) Compounds for Treatment of Cancer JOHNSON M A ~ Y P.L.C. European Appl, 503,830A New trans-Pt(IV) compounds of formula Pt(X2)2(Y),L1L2 where L1 and L2 are amines, but L1 and L2 can not be NH, simultaneously in mutu- ally trans co-ordination sites; X and Y are halogens, OH, ,carboxylates, or o2 is dicarboxylate; (X), and 0, are dicarboxylate, are prepared. The compound is active against cancer cells, particularly against cisplatin-resistant cell lines. Daily dose for humans is 0.1-100 mgkg of body weight, used either alone or in combination with another chemotherapeutic agent.


Compositions Containing Osmium for Treatment of Bacterial or Fungal Infection

Compositions having anti-bacterial and anti-fungal activity and used in the treatment of infection contain 0 s in the 4-6 oxidation state; 0x0, thio, substituted imido or phosphido groups; and alkyl, aryl, phosphine or N-based groups; in admixture or association with a diluent. The 0 s complexes have low solubility in water, but as it is preferably administered in solubilised form a solubiliser, preferably cyclodex- trin, especially Bcyclodextrin, is used.

Liposome Preparations Containing Platinum Complexes for Cancer Treatment

JOHNSON MATTHEY P.L.C. wdd Appl. 92110,177A

SUMITOMO SENAKU K.K. Japanese Appls. 41169,531-32

Liposome preparations used for the treatment of cancers contain a lipid-soluble Pt complex, phospho- lipids and optionally unsaturated fatty acids or their esters. In examples, such preparations contain cyclohexane-1,2-diamine Pt(II) dimyristoate, lecithin and optionally cholesterol. The liposome preparation causes less severe renal toxicity than the regular cisplatin preparation.

New Anti-Neoplastic Agents of Platinum Supported on Calcium Ceramics SANG1 K.K. Japanese Appl. 41178,330 A substance showing excellent anti-neoplastic activity consists of 0.001-30 wt.% Pt supported on Ca ceramics of mcalcium phosphate, Ca monohydrogen phosphate or Ca carbonate. The anti-neoplastic agent can be produced easily and stably, has anti-neoplastic activity equivalent to that of cisplatin, and has low toxicity - in rats LD50 is above 2000 mgikg orally.

New Platinum Complexes with Anti-Tumour Action HOKKO CHEM. IND. CO. LTD.

Japanese Appl. 41178,396 New Pt(1V) complexes including halogen atoms, cycloakyl groups and lower alkylcarbonyl groups are useful as anti-tumour agents effective in the treatment of testicular cancer, bladder cancer, ovarian cancer and other cancers. The complexes have no real toxicity, acute toxicity is low, the therapeutic index is high, and they may be administered orally at a daily dose of 400-800 mglm’ or parenterally at 100-400 mg/m’.

Agent Containing Ruthenium Red for Treating Heart Disease OTSUKA PHARM. co. LTD. Japanese Appl. 41182,432 A new Ca ion dependent cyclic nucleoside phospho- diesterase inhibiting agent has Ru red as the effective substance. The agent is used for the treatment of ischaemic heart diseases such as angina pectoris and myocardial infarction, pulmonary hypertension, ver- tigo and others, and can be administered orally or parenterally at a daily dose of 0.1-300 mgikg.

Palladium Core for Catheter TERUMO COW. Japanese Appl. 41187,160 Core material for a catheter guide wire comprises a flexible top end part made of shape memory TiPd alloy, which has a high flexibility, and a base part. The alloy preferable containing 45.0-51.0 at.% Pd and balance Ti, with 1 .&30.0 at.% Pd being replaced with at least one of V, Cr, Mn, Ni, Fe, Co or Cu. The synthetic resin includes polyethylene, PVC and polyester.

Titanium-Palladium Alloy Core Material for Catheter Guide Wire TERUMO COW. Japanese Appl, 41187,160 A catheter guide wire is obtained by coating a core material with a synthetic resin where the core material consists of a top end part with high flexibility and a base part. The top end part is made of a shape memory TiPd type alloy preferably containing 45.0-51.0 at.% Pd and balance Ti, with 1.0-30.0 at.% Pd replaced with at least one of V, Cr, Mn, Ni, Fe, Co or Cu.

New Anti-Cancer Platinum-Crown Ether Complexes with Lower Toxicity B.K KEPPLER German Appl. 4,041,353 New Pt complexes with crown ether carboxylic acid compounds, for example 1 8-crown-6-tetracarboxy- bis(diammin0 Pt(II)), are used in the treatment of cancer. The complexes have tumour inhibiting prop erties at least as good as cisplatin, are less toxic, more water soluble, and can be given parenterally or orally at 0.1-5 mglday.

Catheter for Epidural Pain Relief R. XAVIER Canadian Patent 2,034,580 A catheter for epidural pain relief has at least two Pt or Ag ring electrodes spaced from the distal end and elecmcally insulated from one another, a wire connected to each electrode, and a pulse generator for applying pain relief pulses via the electrodes. The catheter can provide effective and satisfactory relief from severe pain either temporarily or permanently.

Palladium Alloy for Dental Implant Restorations S. P. SCHAFFER Canadian Patent 2,043,429 Pd-based alloy consists of (by wt.%) 50-90 Pd, 0-3 Pt, 0-37 Au, 0.5-8 Ga, 0.8 In, 0-8 Sn and up to 2 % of a grain refiner selected from Ru, Re and In, or their mixtures. The azloys give good biocompatibility and inertness, do not form galvanic couples with other metals, and have a solidus temperature at > 1 100°C, which allows sufficient temperature between the firing temperature of dental porcelain and the onset of melting of the alloy, to allow soldering.

The New Patents abstracts have been prepared from material published by Derwent Publications Limited.


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Contents...spallation and dissolution in the glass melt, resmct their use. The best combination of properties for use in the molten glass environment are provided by the platinum group