PLATINUM REVIEW · in other directions. The production of staple fibre began in 1930, and by 1940 production was greater than that of continuous filament yarn. Diversification here

PLATINUM METALS REVIEW

A quurterly survey of reseurch o n the platinum metuls urrd of dwelopments in their applications in industry

V O L . 5 J A N U A R Y 1 9 6 1 NO. 1

Con tents

Platinum Alloys in the Production of Viscose Rayon 2

Platinum Reforming Catalysts 9

Cathodic Protection of Water Heaters

Rhodium Plating to Specification I 3

I2

A History of Platinum 18

The Refractory Noble Metals and Rhenium

The Hydrides of Palladium and Palladium Alloys

I9

21

Faraday’s Lecture on Platinum 26

Abstracts 30

New Patents 38

Communications should be addressed to The Editor, Platinum Metals Review

Johnson, Mutthey & Co., Limited, Hatton Garden, London, E.C.1

Platinum Alloys in the Production of Viscose Rayon

J

THE SELECTION OF MATERIALS FOR SPINNING JETS

By J. w. s. Hearle, MA., Ph.D., and A. Johnson, M.Sc.Tech., Ph.n. Manchester College of Science and Technology

In 1884 Count Hilaire de Chardonnet patented a process for making artificial fibres by the extrusion of a solution of nitro- cellulose derived from mulberry leaves, the natural food of the silkworm. These were the first commercially successful man-made fibres, and the production of rayon by this method continued until the last nitro-cellulose factory was destroyed by fire in Brazil in 1949.

Other developments followed rapidly in the closing years of the last century. The cuprammonium process, which is still used to a small extent was patented in 1890, and the patents for the viscose process followed in 1891. In this process, cellulose-usually obtained from wood-pulp-is steeped in caustic soda, aged, and reacted with carbon bisulphide to give cellulose xanthate which is dissolved in caustic soda. The resulting viscose solution is then squirted into an acid bath where it coagulates as the cellulose is regenerated. The filaments so produced are soft and weak, but stretching them increases their strength, and after washing and drying they are ready for use.

The production of viscose rayon was started in Britain in 1905 by Courtaulds. Initially it was an expensive fibre made as a continuous filament yarn which competed with silk. By 1920 world production was 33 million lb per annum, but the price was zoo pence per lb: twenty years later production had increased to 1,200 million lb per annum and the price had fallen to 33 pence per lb. Since then the world production of

continuous filament yarn has doubled again. The technical improvements in ordinary

textile filament rayon during these forty years were marginal, but the versatility of viscose rayon was being exploited extensively in other directions. The production of staple fibre began in 1930, and by 1940 production was greater than that of continuous filament yarn. Diversification here included the making of fibres covering a wide range of lengths and thicknesses, so that they could be spun on cotton, wool, worsted, flax, jute and other spinning machinery. The addition of titanium dioxide could be used to dull the naturally bright appearance, and the introduction of pigments into the spinning solution gave fibres which could be blended into an infinite range of colours.

Another important development was the production of Tenasco-a strong industrial yarn-in 1935. By the end of the war, fibres of this type had almost completely replaced cotton in the big market for tyre-cords.

The years after the war were devoted to increasing the depleted production facilities. However, by 1953, improvements in the strength of rayon were needed to meet the threat of competition from nylon in tyre- cords. Fortunately earlier academic work had provided a basis on which to work.

Rayon is unique among man-made fibres in that its production is accompanied by a chemical reaction-the change from cellulose xanthate to cellulose. By varying the conditions under which the reaction proceeds, it is possible to vary the fine structure of the

Platinum Metals Rev., 1961, 5, (l), 2-8 2

Many thousands of platinum alloy spinning jets are in use in n modern viscose rayon plant. illustration shows one unit engaged in spinning continuous $lament in a Courtaulds factory

The

fibres. Ordinarily, rayon has a structure composed of separate skin and core. In the skin the texture of the arrangement of the long- chain molecules in crystalline and non- crystalline regions is finer than in the core, and by increasing the proportion of the skin structure, stronger fibres can be made. This and other improvements have resulted in a rise in the strength of rayon tyre-cords from 25 lb to 40 lb, and have succeeded in maintaining the price advantage of rayon over nylon in tyres.

Similar developments are taking place, although more slowly, in textile rayons. All- skin fibres should have greater durability, and their round cross-section changes the appearance and reduces soiling. All-core fibres such as the so-called polynosic fibres have much better dimensional stability, especially on wetting. And fibres with an asymmetrical skin have a permanently built- in crimp. Other techniques give a collection of fancy yarns.

Viscose rayon is not really one type of fibre: it is a great variety of fibres which have a vast range of uses-dress-wear, furnishings,

carpets, blankets, non-woven fabrics for interlinings, surgical swabs, filter fabrics, ropes, hose-pipes, conveyor belts-the list is too long to complete. Rayon is now second only to cotton in its scale of production and diversity of applications.

The Heart of the Process The heart of the rayon production process

is the spinning jet through which the viscose solution is extruded into the coagulating solution.

The compositions of these two solutions vary somewhat according to the particular type of viscose rayon being made, but a reasonably typical viscose would contain about 6.5 per cent of alkali in the form of sodium hydroxide and about 7.5 per cent of cellulose (present, of course, as the xanthate). The coagulating solution is essentially dilute sulphuric acid containing about 10 per cent by weight of the acid, together with about 20 per cent by weight of sodium sulphate and smaller amounts of zinc sulphate and glucose, the remainder being water. Thus the spinneret is subject on the one side to about

Platinum Metals Rev., 1961, 5, (l), 3

A simple demonstration of the formation of a multi-jihment yarn by pumping viscose solution through the holes in a jet immersed in an acid bath (Courtaulds Ltd)

1.5 N sodium hydroxide and on the other to about 1.5 N sulphuric acid.

These are both severe conditions, which bring about chemical attack of most metals. The use of steels, for example, is immediately precluded for the manufacture of spinnerets for viscose rayon. In this respect, viscose differs from other manufactured fibres where steel spinnerets may be used.

Thus, for the manufacture of cellulose acetate filaments, the spinning solution consists simply of the acetate dissolved in either acetone or methylene chloride, both of which are without chemical action on steels. The solution is extruded into warm air, when the solvent evaporates, so again there is no corrosive action corresponding to that of the acid coagulating bath in viscose rayon manufacture.

A process more akin to viscose spinning is the manufacture of cuprammonium rayon.

In this case a solution of cellulose in cuprammonium hydroxide is used, but although the final coagulation of the filaments requires an acidic bath they are first spun simply into water. Thus, the spinneret is not in direct contact with acid, and so may be fabricated from steel. Another difference between the cuprammonium and viscose processes which permits steel to be used for the former concerns the diameter of the holes in the spinneret. In the cuprammonium process this is of the order of 0.8 to 1.00 mm, whereas in a viscose spinneret the diameter may be as small as 0.03 mm, so that the removal of metal by corrosion is of greater significance.

Resistance to Chemical Action To return to the viscose process, we can

see that spinnerets must be fashioned from materials that are capable of withstanding the simultaneous chemical action of 1.5 N


caustic soda and 1.5 N sulphuric acid. So far as metals are concerned, this at once limits the choice to the noble metals, platinum and gold, and some of their alloys, and also tantalum protected by an oxide film.

Two alloys in particular have been widely used; 10 per cent rhodium-platinum and 30 per cent platinum-gold. The former, because of its higher cost, is normally restricted to use where the conditions are most exacting and the cheaper one is used where the conditions are less critical.

However, although such alloys will resist direct chemical attack by acid and by alkali, and on that account are suitable for spinneret manufacture, other factors also have to be taken into consideration. One of these, and one which mitigates against the use of any metal for spinneret manufacture, is the occurrence of electrochemical phenomena.

In the viscose process, one side of the spinneret is in contact with an alkaline solution and the other with an acid, and the two solutions form a junction inside the bore of the spinneret. If the spinneret itself is an electrical conductor (i.e. a metal), the system

The number of holes and their pattern in a jet vary according to the type of rayon to be produced. This type of platinum-gold alloy jet has over 2,000 or$ices and is made and used in the production of staple .fibre

by Courtaulds Ltd

Platinum Metals Rev., 1961, 5, (l),

behaves as an electrical cell, most simply regarded as a form of hydrogen ion concentration cell. As with all concentration cells, the electrode in contact with the more concentrated solution will assume a positive charge, so that the spinneret becomes polarised, the surface in contact with the alkaline solution bearing a negative charge and that on the acid side a positive charge.

With steel spinnerets, of course, these electrochemical effects would in themselves cause corrosion, enhancing the deleterious effects of direct chemical attack. The noble metals are not corroded, but nevertheless a current will flow, resulting in electrolysis of the viscose solution passing through the jet. The most serious result is that the negatively charged xanthate ions will be attracted to the positive surface of the spinneret, where they will be discharged and decomposed, ulti- mately giving rise to a ring of cellulose block- ing the jet. Some deposition of sulphur also occurs, but this may arise from the noimal decomposition of the xanthate in the acid solution rather than electrolytically. The acid coagulating bath penetrates some distance

5

up the jets, so that coagulation and the pre- cipitation of insoluble solids actually begins in the jet. Thus, although noble metal jets are durable and represent a considerable improvement over steel, they are not entirely without disadvantages. Naturally, a great deal of effort has gone into devising ways of overcoming these defects. There have been two methods of approach: first to avoid the electrochemical effects which are responsible for deposition and blockage, and secondly to prevent deposition while allowing the electrolysis to continue.

One obvious method of avoiding electrical effects is to fabricate the spinneret from a non-conductor. The material must also withstand thc direct attack of the alkaline and acidic solutions as well as possessing the requisite mechanical properties. Most attention seems to have been paid to the use of synthetic rubies, and ceramic spinnerets are

Piercing, forming and polishrng the holes in a spinning je t are intricate operations demanding considerable skill and accuracy. Here one of the operators i n the Johnson Matthey je t production shop is broaching the holes i n small rhodium-platinum alloy je ts for spinning tyre-cord. The built- i n binorular microscope is a

Jeature of the instruments used to pierce and f o r m the jet holes

also seriously considered. The major difficulties are probably connected with piercing these materials with the necessary precision. A similar method of approach is to coat the spinneret with a non-conductor, and silicone fluids are now being investigated for this purpose.

Another method of avoiding electrical effects is to neutralise the charges on the spinneret by passing a current in the opposite direction. A more satisfactory method is to make the spinneret as a whole carry a large charge relative to some other conductor in contact with the liquid. This is most easily done by using the lead lining of the coagulating bath as the second electrode -the cathode-and applying a potential of the order of I to 1.5 volts. In this way, choking of the jets can be prevented for periods of up to four weeks.

In practice, however, the most usual


method of avoiding deposition on the spinneret is by the addition of anti-fouling agents to the viscose solution before spinning. These are dispersing agents which serve to hold solid particles in solution during the short interval of time between the entry of the viscose into the spinneret and the formation of coagulated filaments.

Mechanical Properties So far, only the chemical and electrical

requirements of spinnerets have been considered, and we have seen that these can, in the main, be met by the use of noble metals. Finally, attention must be paid to the mechanical properties required of a satisfactory spinneret. For the production of good quality filaments the spinning jets must be made with great accuracy and possess a high surface finish and maximum durability. The accuracy required in the piercing of the holes demands a material which is completely uniform in structure, while the attainment of highly polished surfaces requires as small a grain size as possible. It is these two properties which the metallurgist must seek, allied with a convenient method of producing the necessary hardness to give durability.

The blank caps are normally produced from strip by conventional presses, and should at that stage be uniform in thickness and have a high surface polish, particularly on the inside face.

According to the metal used, piercing of the jets may be carried out with the metal in the hard or softened form. Piercing is naturally simpler with a soft cap, but can only be done this way if the pierced cap can subsequently be hardened without affecting the size and internal surface finish of the holcs themselves.

The 10 per cent rhodium-platinum alloy, while possessing excellent resistance to corrosion, unfortunately has a relatively large grain size and this causes difficulties both in drawing and piercing and also in obtaining the necessary high polish. An alternative dloy having the same high corrosion resistance but

Platinum Metals Rev., 1961, 5, (l),

a much smaller grain size is 3 pzr cent ruthenium-platinum. Piercing is simpler and thefinishedspinneret canbe givena high polish.

The widely used 30 per cent platinum-gold alloy presents little difficulty in working and will take a high polish. Traditionally the alloy has been rolled to a hardness of approximately 180 Vickers before pressing the caps, the holes then being pierced through the hard face. However, the addition of a small percentage of rhodium produces an alloy that can be worked to a fine-grained structure having a hardness of only about 120 Vickers. This is accomplished by a carefully controlled cycle of rolling, annealing and solution treatment. Caps are produced and pierced from this relatively soft material and then, by a suitable heat treatment, brought to a hardness of around 220. This process combines the simplification of piercing associated with the soft alloy with the desirable properties of the fully hardened form. Increasing the platinum content of the alloy to 35 per cent permits the manufacture of spinnerets with a final hardness of around 280 Vickers, while for special purposes alloys containing from 40 to 50 per cent platinum are also used.

The number of holes and their pattern in

7

the jet vary according to the type of rayon to be produced. Typical figures range from less than IOO holes per jet for textile rayon, from 650 to 1,500 for tyre-cords and to as high as 6,000 for staple manufacture. The shape of the holes is much the same for all types of rayon, and it is, indeed, of great importance if satisfactory filaments are to be obtained. The lead-in diameter is always somewhat greater than that of the major part of the orifice, and considerable care is needed to ensure completely smooth blending of the lead-in with the straight capillary. The maintenance of a sharp junction between the capillary and the outlet face is also a critical feature. To achieve this, the outer facc is carefully polished after piercing, the holes themselves being filled with glass or some other material that can readily be removed by melting, in order to protect the polish of the jet walls from the abrasive. In jets produced by Johnson Matthey, for example, orifice diameters may be as-small as 0.03 mm and

Newly formed viscose ruj on thrends being led out of the cougu- luting bath on a textile-type continuous spinning machine in one ?f Coiirtaulds factories

are accurate to within I 0.0015 mm on all diameters.

Although it is very likely that many new manufactured fibres will make their appearance, and even that existing fibres will be modified in various ways, the development of radically different spinning arrangements seems improbable. Drastic changes in the nature of spinnerets are therefore also unlikely, and it seems most probable that the main advances will be metallurgical, leading to alloys having even more desirable properties, both during manufacture and in use. There always remains the possibility of using non- conducting materials. Artificial gem-stones would be satisfactory if the difficulties of piercing them could be overcome. Another possibility, at present, perhaps more remote, lies in the use of a synthetic polymer. How- ever, in spite of these possibilities, it seems likely that noble metal alloys will remain the only suitable materials for viscose rayon spinnerets for many years to come.


Platinum Reforming Catalysts PRODUCTION OF HIGH-OCTANE FUELS AND OF AROMATIC CHEMICALS

To meet the steadily increasing compression ratios characteristic of modern automobile engine design the petroleum industry is faced with the problem of producing high-octane fuels at the lowest possible cost. To achieve this end, catalytic reforming processes are employed, followed by the addition of tetra- ethyl lead to the reformates and the blending of refinery products of high-octane number such as a range of aromatic alkylates. The same processes that are employed for up- grading low-octane napthas may also be used as a valuable source of aromatics for the chemical industry.

Newer developments in these processes have been almost entirely towards increased operating severity. These include feedstock pre-treatment with process hydrogen to re- move sulphur and trace elements which poison catalysts, the developihent of new catalysts especially with higher platinum contents and the use of lower space velocities. Alkylation processes are expected to contribute to a greater extent to the production of higher grade fuels, and isomerisation processes will probably rise in importance. The growth of the petrochemical industry will be responsible for some of the expansion of platinum reforming processes.

The following processes are available for up- grading petroleum stocks:

(I) Catalytic reforming (2) Reformate splitting (3) Alkylation (4) Isomerisation (5 ) Extraction of pure aromatics (6) Blending of products obtained in (I) to

Eleven catalytic reforming processes have ( 5 ) above.

been developed, of which Only four do not

As part of a two-day symposium in Liverpool organised by the Society of Chemical Industry on “The Manufac- ture and Use of some Catalysts in the Petroleum and Petrochemical Indus- tries”, M r . H . Connor of Johnson, Matthey & Co., Limited presented a paper on “Platinum Reforming Cata- lysts”. Dealing both with the use of platinum reforming processes to yield high-octane fuels to meet the requirements of modern internal combustion engines and with the growing production

materials or intermediates for the chemical industry, the author outlined the principles of platinum reforming and described the major processes that have been developed. A summary of his

paper is given here.

by this route of aromalics as raw

employ platinum group metal catalysts; these latter account for less than 10 per cent of the installed reforming capacity of the world.

Platforming, the first platinum reforming process developed, accounts for over 50 per cent of installed capacity. As requirements for increased operating severity increase, however, the newer regenerative processes are beginning to rise considerably in importance.

Platinum Reforming The primary purpose of catalytic reforming

is the conversion of low-octane number hydrocarbon fuel to high-octane fuel. Several reactions contribute to this increase in octane number, but the most important in platinum reforming are as follow^^


(I) The formation of aromatic hydrocarbons from paraffins and cyclic compounds

(2) The formation of branched-chain paraffins from straight-chain paraffins.

The individual chemical reactions occurring in platinum reforming and the mechanisms by which platinum catalysts bring them about include the following.

Hydrogenation of Olefins The straightforward reduction of the double

bond (or bonds) present in paraffinic olefins is rapidly achieved by platinum catalysts. The reaction requires low operating seventy and the resultant saturated straight- or branched- chain paraffins are then available for other reactions, e.g. isomerisation, cyclisation, etc.

Dehydrocyclisation The formation of aromatics from paraffins

o c w s by the linking of carbon atoms with the elimination of hydrogen.

Isomerisation of P a r a s Branched-chain paraffins have considerably

higher octane numbers than their corresponding n-isomers and the isomerisation of the latter is an important function of platinum reforming. In most instances, however, paraffins present in feedstock are already present as mixtures of isomers, hence the isomerisation activity of a catalyst is important chiefly for the isomerisation of cyclopentane derivatives.

Isomerisation of Napthenes Naphthenes, in particular cyclopentane

derivatives, constitute a high proportion of feed naphthas. The isomerisation of these compounds to C, structures and the aromatis- ation of the latter are the most important reactions contributing to an increase in octane number of a feedstock.

Hydrocracking Under the conditions of platinum reform-

ing, cracking competes with dehydrogenation

reactions. Since high hydrogen pressures are employed, any olefins that are fomcd are saturated immediately and the reaction is generally termed “hydrocracking”.

Platinum Reforming Processes Various oil companies have developed a

number of commercial reforming processes employing platinum catalysts. The most important of these are described below.

Platforming The Universal Oil Products Company

introduced in 1949 the first platinum reforming process, termed Platforming. Today, although several other processes exist, Plat- forming still accounts for the greater part of platinum reforming operations. It employs a catalyst consisting of platinum on alumina with a small but critical percentage of halogen added to maintain correct balance between conversion of paraffins by dehydrocyclisation, hydrocracking and isomerisation.

Platforming raises the research octane numbers of feed napthas from 30 to 50 to over 90 with 85 to 95 per cent yields. This is a fixed bed, non-regenerative process, operating at 850 to 950°F and at 200 to 700 psig. Catalyst life may exceed 200 bbl. per lb catalyst, although lower values are usual.

Ultraforming Ultraforming was developed in 1954 by the

Standard Oil Company (Indiana) and is a fixed-bed cyclic regenerative process. It employs a 0.6 per cent platinum on alumina catalyst and operates at low pressures, 200 to 300 psig. Usually five reactors with a “swing” reactor are employed, enabling regular regeneration in situ to be carried out. The relatively high rate of decrease in catalyst activity necessitates frequent regeneration- up to 30 to 40 regenerations are possible with a total catalyst life of 150 to 240 bbl.!lb.

Powerforming Powerforming was developed by the Esso

Research & Engineering Company utilising


a catalyst manufactured by the Davison Chemical Company. It is a fixed-bed regenerative system producing a reformate of octane number IOO and over. Operating pressure is 300 to 600 psig with catalyst temperatures 900 to I O O O O F using a platinum- alumina-halogen catalyst. The conversion of paraffins is more complete at low pressures and high temperatures, which are conditions also favourable to the formation of aromatics.

Houdriforming Houdriforming was introduced by the

Houdry Process Corporation, Philadelphia, in 1950 and is a fixed-bed reforming process employing a platinum-alumina catalyst. It operates with a catalyst temperature of 875 to 950°F and an operating pressure of 250 to 600 psig. A desulphurised feed is generally used and high conversion efficiencies are obtained yielding a reformate of research octane number exceeding 90.

Penex-Platforming The Penex process was introduced by

Universal Oil Products as a means of isomeris- ing the unchanged n-pentane and n-hexane obtained from platformates. Pentane and hexane are separated from the latter and passed once through a bed consisting of a dual-function platinum-alumina (“ 1-3”) catalyst. By isomerisation the octane number of an n-pentane feed may be raised from 62 to 93, that of n-hexane from 25 to 100. Complete isomerisation is not possible, but the high activity of the catalyst allows conversion at lower temperatures which favour the equilibrium.

The Iso-Kel Process This process, developed by M. W. Kellogg

Company, is also specifically for the isomerisation of n-pentanes and n-hexanes. It employs a precious metal, non-platinum catalyst as of 1116th inch extrudates and operates at 700 to 850°F~ IOO to 750 psig pressure.

The Butamer Process The Butamer process was developed by

Universal Oil Products for the isomerisation

of n-butane to iso-butane over a platinum- containing catalyst. Over 40 per cent of the feed (n-butane) is converted to iso-butane in a single pass.

Production of Aromatics Aromatics for the chemical industry had

been produced during the first half of this century primarily from coal. The tremendous increase in size of the chemical industry during the past twenty years, however, has coincided with a similarly rapid growth of the petroleum industry. The platinum reforming processes described in the foregoing paragraphs are able to produce a large range of aromatics which may be separated from each other and from unchanged feed by fractional or extractive distillation.

Today the total world production of aromatics from petroleum somewhat exceeds production from coal.

In the United States 35 per cent of benzene is produced from petroleum, 78 per cent of toluene, 90 per cent of xylenes and 12 per cent of phenol. The bulk of petrochemical aromatics is obtained from virgin naphtha or catalytically reformed naphthas-very little from catalytically cracked napthas.

There are several aromatic chemicals whose large-scale production by platinum reforming is not so well developed as that of others. For example, very little use is made at present of compounds such as monocarboxylic aromatic acids, aromatic alcohols and aromatic aldehydes compared with the large-scale utilisation of other substitcted aromatic materials, e.g. chlorobenzene, phenol, styrene. In addition, no important use has been found so far for the C, or C,, aromatics from reformates other than for cumene production for phenol and acetone manufacture via cumene hydroperoxide.

Several processes have been developed which combine platinum reforming with extraction or extractive distillation to produce aromatics. One such proccss, Rexforming (Universal Oil Products), employs an aqueous


glycol solution to solvent-extract aromatics and light high-octane paraffins.

Manufacture of Platinum Reforming Catalysts

Each platinum atom in a petroleum reforming catalyst is required to perform a tremendous catalytic feat. In addition, although constituting less than I per cent of the catalyst, the platinum must maintain this active and selective performance over the entire time it is in a reforming unit. It is not uncommon to have a catalyst life of two years or more, so that on average each platinum atom has catalysed the conversion of more than twenty million hydrocarbon molecules. The platinum cannot perform in this way if it is inaccessible, or poisoned, or in too large crystallites, or in a position which makes it ineffective against coke formation.

The following factors influence the activity of a platinum reforming catalyst, and their accurate control has been the subject of much study and very numerous patent applications:

(a) Platinum concentration and distribution ( b ) Phase-type of alumina support, its

specific surface, density and pore- characteristics

(c) The nature and concentration of halogen or other additive which serves to modify the acidity of the support

(d) The manner in which the support is prepared and by which it is impregnated with platinum and halogen

( e ) The particle size, shape and bulk density of the finished catalyst.

The platinum concentration is a critical factor in determining catalyst costs, and concentrations from 0.3 to 1.3 per cent are usual. Increasing the platinum concentration raises the aromatics production by raising somewhat the dehydrogenation activity (not in direct proportion).

The paper concludes with a survey of the extensive patent literature relating to platinum reforming catalysts and their manufacture and some notes on the methods of recovering platinum from spent catalysts-a subject vital to the economics of platinum reforming. The full paper (published in Chemistry and Industry, 1960, 1454 - 1472) includes 280 references to the literature.

Cathodic Protection of Water Heaters USE OF PLATINUM-PROTECTED TITANIUM ANODES

The short life, due to corrosion, of gal- vanised iron domestic water tanks has led to the development of glass-lined water heaters in the United States. Less serious tank corrosion caused by small holes in the glass linings may be controlled by the use of a cathodic protection system requiring a small impressed current. The design of such a system is discussed in a recent paper by H. C . Fischer of the Thermo-Craft Corpora- tion, New York (Corrosion, 1960, 16, (g),

It has been found that the bare area of a single-coated, glass-lined tank may be protected adequately by a current of 5 milli- amperes even in waters of high resistance. The presence in the system of copper ions derived from copper plumbing gives rise to local cell corrosion which renders magnesium and zinc anodes unsuitable. However, at the

9-17).

low current densities required, non-sacrificial anodes of bare titanium or titanium wound with platinum-clad tantalum ribbon have proved both effective and economic. One anode described consists of a 30-inch titanium wire, 0.051 inch in diameter, around which is wrapped a 0.002 by 0.008 by 36- inch platinum-clad tantalum ribbon. Field trials are being conducted using platinum- plated titanium wire anodes which have proved satisfactory in preliminary tests.

Cathodic protection has been found effective for glass-lined domestic water tanks heated either electrically or by gas. Power for the impressed current system for gas water heaters is supplied by a thermoelectric generator. In this case, in order to keep the anode voltage as low as possible, only platinum-plated titaniumor the platinum- tantalum-titanium anodes may be used.

Platinum Metals Rev., 1961, 5, (1),12-12 12

Rhodium Plating to Specification By li. K. Benham, F.R.I.C.

.John~on, Matthey & Co., Limited

The Ministry of Aviation has recently issued Process Specijcation DTD 931, covering the rhodium plating of silver, copper, steel and aluminium components primarily for electrical and electronic applications. This article reviews the specijication and outlines recommended procedures for the successful preparation of rhodium electrodeposits.

The electrodeposition of rhodium is conducted on normal plating lines and, at least for the thinner deposits, there are no special difficulties. I t is some twenty-five years since the process was first carried out on a commercial scale. Originally it was chiefly used on jewellery to provide a white non- tarnishing surface of high reflectivity; for this purpose deposits of only 0.000005 to o.oo0010 inch were adequate, and fortunately were relatively free from porosity. In addition the great hardness of electrodeposited rhodium gave an excellent resistance to wear.

Within a few years it was found that the complete freedom from tarnish characteristic

of rhodium, coupled with its excellent resistance to abrasion, provided just the right combination of properties required in certain types of sliding or rubbing contacts in electronic equipment, and a demand arose for thicker deposits than had formerly been needed. The Second World War, with its rapid development of radio communication and radar, led to an enormous increase in the amount of rhodium used for this type of application and to the appearance on many engineering drawings and individual specifica- tions of a note calling for such-and-such a thickness of electrodeposit.

In using a high-cost metal such as rhodium

A group of typical electrical and electronic components with rhodium plated contact surfaces


Masking of surfaces not required to be plated i s carried out with a chlorinated rubber paint

a good deal of discrimination naturally needs to be used in deciding on the appropriate thickness of deposit to meet any particular set of design requirements, and in the earlier days of its employment there was sometimes a tendency for users to settle upon one arbitrary thickness to meet a variety of conditions. Much more information is nowadays available on the thickness of rhodium suitable for a particular application, and it is well understood that thicknesses may range from a minimum of, say, O.OOOOI inch for the protection of a silver surface from tarnish up to something over 0.001 inch where heavy mechanical wear is to be met with.

This variation in optimum thickness was recognised to some extent in the Ministry of Supply Inter-Service Specification RCS/IOOO (now replaced by Defence Specification DEF-~OOO), “General Requirements for Service Telecommunication Equipment”, which called for a rhodium thickness of 0.00015 inch over a silver undercoating, but added that special requirements might be demanded where unusually heavy wear was to be encountered. Where an untarnishable

surface was required without wear-resisting qualities, the thickness of rhodium was specified as a minimum of O.OOOOI inch. This specification made no reference, however, to the methods or procedures to be adopted in producing rhodium electrodeposits.

The recent issue by the Ministry of Avia- tion of Process Specification DTD 931, “Rhodium Plating” fills this gap and pro- vides both users and electroplaters with a comprehensive guide to the factors involved in the successful use of rhodium.

Basis Metals and Undercoats Most of the metals and alloys commonly

used may readily be rhodium plated directly, although for reasons of skin conductivity, exposure to high temperatures or other special requirements it is more usual to deposit first an undercoating of silver or less frequently of nickel.

The exceptions to this include steel and aluminium, which are readily attacked by the strongly acid plating bath unless a dense non- porous undercoating of silver or nickel is first applied. Masking materials such as lacquers


or chlorinated rubber paints are not sufficiently protective when the rhodium plating time is more than a few minutes. For the deposition of say 0.00025 inch of rhodium this may be of the order of I to I* hours, and much damage could result in this time unless the steel or aluminium were completely protected. ‘The specification therefore calls for a deposit of silver, copper or nickel not less than 0.001 inch in thickness for steel or 0.0015 inch for aluminium after polishing.

The choice of undercoat for rhodium is often dictated by the application. Thus, as already mentioned, silver is specified when the plated component is to be used in a high- frequency circuit. Here, particularly at very high frequencies, the “skin effect” is pronounced, the current being concentrated more in the outer skin of the conductor as the frequency increases. In certain very high frequency circuits the thickness of rhodium may therefore have to be restricted because

Tin-lead solders also present a problem in of its inferior conductivity compared with that that unless they are completely covered with of silver (35 per cent IACS against 106 per a non-porous undercoat before immersion in cent). The choice of rhodium thickness then the rhodium bath a dense black stain is becomes a compromise between the con- produced on the solder and over an appreci- flicting requirements of long life and con- able area around the joint. A similar require- ductivity. ment of a minimum deposit of silver, copper Silver is also the preferred undercoat to or nickel is therefore specified on all areas of minimise the possibility of cracking in thick soft solder. rhodium deposits. Where the application

As soldered joints are frequently located on involves conditions of exposure to high temp- the inside corners of assemblies to be rhodium eratures, however, such as in reflectors of plated, it is essential that allowance be made various kinds, a nickel undercoat is to be for the fact that less silver will deposit in ‘such preferred. areas by comparison with the average thickness over the whole component. It would appear to be the tin content of the solder that gives rise to the problem, and where possible the use of a tin- silver-lead solder containing no more than 5 per cent tin is to be preferred.

The writer has found that only 0.0001 inch of silver is adequate before rhodium plating over joints made with this alloy, while they may even be plated directly with no more than a very slight yellow- ing of the rhodium over the soldered area. A straight 5 per cent silver-lead solder is completely satisfactory for direct rhodium plating but is rather more difficult to use.

Rhodium plating a batrh of electrical contart springs

Platinum Metals Rev., 1961, 5, (l), IS

Preparation for Plating The degreasing and alkaline cleaning

procedures given in the D T D specification follow the normally accepted practice for these operations, but with rhodium plating very great care must be exercised to ensure thorough cleaning, or poor adhesion of the deposit may result. When thick deposits of rhodium are to be applied an additional etching step may well be incorporated, such as the anodic etch in cyanide for silver and the immersion in a ferric chloride-hydro- chloric acid solution for nickel described in an appendix to the specification. Activation of nickel by cathodic treatment in sulphuric acid (say 10 per cent by volume) at 20 to 25 amperes per square foot for half a minute is also beneficial. Work so treated should be transferred without rinsing with as little delay as possible into the rhodium solution. I t is the writer’s experience, however, that adhesion on nickel is inferior to that to be obtained on silver even when these etching treatments have been used.

For stopping-off materials, either chlorinated rubber paints or special cellulose lacquers are to be recommended, but wax is not satisfactory. The edge of the stopping-off

paint should never be immediately adjacent to the essential contact area, but should be brought to within about one-sixteenth inch of this area. Rhodium deposits adjacent to stopping-off materials are sometimes found to be defective and this small margin is helpful in reducing the possibility of failure on this score. When using chlorinated rubber paint, stoving for two or three hours at 160°F effectively removes solvents in the paint film and also reduces the possibility of failure. When parts are stopped-off it is also advisable to use a cold cleaner to prevent the paint or lacquer from “frilling” at the edges.

Plating Procedure The concentration of rhodium in the

plating bath, its temperature, and the current density at which it is operated may be varied over quite a wide range. For the production of thick deposits, a high metal content and a low current density are to be preferred, especially when pinholes in the deposit must be avoided. This particular defect is also minimised by regular tapping of the work bar to dislodge hydrogen bubbles adhering to the surface. Alternatively, it is possible to fit a cam, operated by a fractional H.P. motor, to

Recommendations for Rhodium Thickness and Electrolyte Composition

Class No.

Rh 15

Rh 25

Rh 100

R h 200

Rh 400

Rh 800

General Type of Application

Minimum Thickness on Agreed Significant Surfaces (inch)

Tarnish protection . . . . Reflectors . . . . . .

Light mechanical loading and infrequent use .. . .

Medium mechanical loading..

Heavy mechanical loading . . Very heavy loading conditions

in special applications only

0.0000 I5

0.000025

0.000 I

0.0002

0.0004

0.0008

Recommended Rhodium Content, gmllitre

1 2 I

Recommended Minimum Sulphuric

Acid Content, mi l l i t re

20

20

50

16 Platinum Metals Rev., 1961, 5, (1)

lift the work bar say one inch and then drop it back on to the top of the vat at intervals of about 20 or 30 seconds.

Thin deposits may be obtained from a more dilute solution, thus economising in the amount of metal tied up, and higher current densities are satisfactory. The specification recognises these variables, and to some extent correlates recommended electrolyte compositions with thickness of metal to be deposited. The table on page 16 combines the suggested rhodium and sulphuric acid concentrations appropriate to the thicknesses of deposit set out in the specification.

The electrolyte is recommended to be operated between 30 and 50°C, with a cathode current density of 10 to 20 amp.,/sq.ft., although in special cases a reduction to 5 amp./sq.ft. is preferable.

Rhodium plating is an insoluble anode process, the anodes normally being of platinum or rhodium-platinum, and the metal deposited from solution must therefore be replaced by the addition of rhodium sulphate concentrate. The specification calls for this replenishment to be made before the rhodium content of the bath has fallen by TO per cent of its nominal value. Attention to this is most important, as if proper replenishment is not carried out the cathode efficiency of the bath will fall and less rhodium will be deposited, other things being equal. The best practice is to add the necessary quantity of concentrate immediately after the completion of each batch of work. Periodic chemical analyses of the solution should be made to ensure that the correct rate of replenishment has been achieved, and reliable methods for the determination of rhodium are given in an appendix to the specification.

It is also of utmost importance to carry out regular checks to determine the rate of deposition, or in other words to control the thickness being deposited in a particular set of operating conditions. Failure to observe this requirement can lead either to the deposition of more rhodium than is necessary and so to needless COY, or of course to less-and

failure to meet specification. The simplest means of control is to weigh a piece of copper foil before and after plating for a known time at a given current density, and a further appendix gives the simple formula to be applied.

Thickness Recommendations The thickness of rhodium deposit called

for by the user should naturally bear a relation to the application or service duty involved. Too often the phrase “rhodium flash” has been employed to cover requirements ranging from the thinnest plate for tarnish prevention to a heavy deposit needed to withstand heavy mechanical wear. The specification adopts six classes of deposit to give guidance to engineers and designers in selecting an appropriate thickness. These recommendations, reproduced in the table, will undoubtedly be of value to users and potential users of electrodeposited rhodium.

Naturally the thicker deposits are normally restricted to the areas where they are actually required, but in many cases it is usual to apply a thin tarnish-preventive deposit over the remainder of the part.

It should also be said that the heavier deposits, from say 0.00025 inch upwards, require considerable care and experience to produce sound plates free from fine hair cracks. Rhodium as deposited is normally in a state of considerable mechanical stress. Where excessive cracking is due to organic contamination, either from stopping-off paints or other sources, treatment of the solution with activated charcoal is usually effective.

Inspection Requirements The inspection clauses of the specification

cover freedom from surface defects, reflectivity, adhesion, hardness and thickness of the deposit.

The question of surface appearance is usually a matter of opinion, and it is often found advisable for the plater to discuss requirements with the user and to agree on an acceptance test. The present specification


allows the presence of fine hair cracks, particularly in deposits thicker than 0.0001 inch.

A bend test is laid down for the assess- ment of adhesion, but the specification draws attention to the fact that the rhodium deposit may well crack on bending and that a distinction must be made between such cracking and actual exfoliation.

The hardness of electrodeposited rhodium is extremely high-of the order of 800 to 900 Vickers-but it is naturally extremely difficult to determine hardness values on very thin

electrodeposits. The specification accepts this difficulty for deposits less than 0.0004 inch in thickness, but for thicker deposits states that the hardness, as determined by a suitable micro-hardness tester, may be checked at the discretion of the inspector.

Owing to the chemical stability of rhodium the only means of measuring the thickness of a deposit is by a destructive method. Mounting and sectioning, followed by measurement with an eyepiece graticule or direct measurement of a photomicrograph, is the specified method.

A Historv of Platinum J

LATINUM, by comparison with metals P such as copper, silver and gold, has a relatively short history, but there is none the less a fascinating story to unfold in tracing the be- ginnings of an understanding of its character and in outlining its commercial exploitation.

It was not until the Spanish conquest of South America that rumours were heard of a new metal that could not readily be melted, the first published reference occurring in 1557 in the writings of the Italian scholar and poet Julius Caesar Scaliger. Only in the middle of the eighteenth century were specimens of this metal received in Europe and subjected to proper scientific examination, first by the Englishman Brownrigg and then in quick succession by chemists in France, Germany, Spain and Sweden.

Much effort was then directed towards the refining, melting and working of platinum, culminating in the well-known work of Wollaston, early in the nineteenth century, in producing malleable platinum by the technique nowadays known as powder metallurgy.

From then on the pace quickened and the commercial development of platinum, its sister metals and its alloys really began; the discovery of catalysis by Dobereiner, the introduction of the melting of glass in platinum vessels by Faraday, the design and manufacture of enormous platinum boilers for the concentration of sulphuric acid by Johnson and Matthey are but a few of the outstanding features along the way.

In A History of Platinum, published bv

Two illustrations from Donald 1WcDonald’s“AHistoryofPlatznum”. Above, Julius Caesur Scaliger. the Italian scholar whose writings In- cluded the fcrst reference to platinum, published i n 1557. Below, the P T P S S

used by W’ollaston to compress platinum powder into cakes before forging

Johnson, Matthey & Co., Limited (35s or $5.50j, Donald McDonald has, by diligent research into both published literature and private archives, succeeded in putting together a clear and readable account of these developments that has never before been given as a continuous story.


The Refractory Noble Metals J

and Rhenium ALLOYING POSSIBILITIES WITH MOLYBDENUM AND TUNGSTEN

The four scarcer platinum group metals- rhodium, ruthenium, iridium and osmium- have higher melting points than platinum and palladium, they are more resistant to acid attack (in massive form they are virtually insoluble in aqua regia) and mechanically they are stronger and much less ductile. In the past, they have thus often been referred to as the “insoluble” platinum metals. How- ever, in a recent paper presented by R. I. Jaffee, D. J. Maykuth and R. W. Douglass at the Refractory Metal Conference of the American Institute of Metals in Detroit in May 1960, attention is drawn to the relationship between these metals and the neigh- bouring transition metal, rhenium. “It is apparent,” write the authors, “in considering rhenium and the (above four) platinum-group metals we are really talking about one family”; and they propose that the family should be termed the “refractory noble metals” .

The authors present an excellent comprehensive review of the literature dealing with the mechanical, physical and chemical properties of this group of metals, emphasising always the transition found in properties between members of the group.

Resistance to Oxidation One feature of the group that frequently

needs to be considered concerns oxidation resistance. Although the group is rightly placed among the noble metals, the oxidation resistance ranges from that of rhodium, one of the most oxidation-resistant of all metals, to that of rhenium, which is among the most readily oxidised. The authors point out, however, that “despite this vast difference in oxidation hehaviour, the mechanism of oxida-


tion of the noble metals is remarkably con- sistent. A volatile oxide forms at temperatures above the oxide decomposition temperature, and metal loss is due to oxide volatilisation and metal vaporisation”. Nearly all other metals form stable oxides.

More than half of the review is concerned with the alloying behaviour of the refractory noble metals with each other and with other elements. Arising from this extensive review, the authors particularly note the very remarkable, and indeed spectacular, effect of additions of rhenium on the working properties of molybdenum and tungsten. This was first noted by Geach and Hughes, working in the laboratories of Associated Electrical Indus- tries, who found that molybdenum when alloyed with 50 per cent by weight of rhenium could be cold-rolled to sheet direct from the cast condition and that tungsten alloyed with 30 per cent by weight of rhenium could be rolled at slightly elevated temperatures. The amounts of rhenium that need to be added are, it will be seen, very large, and the authors have accordingly been responsible for initiating at Battelle Memorial Institute, under the sponsorship of the Office of Naval Research, an investigation into the possibility that similar effects might be produced by adding smaller amounts of the refractory platinum-group metals.

Improving Ductility The effects of rhenium additions in im-

proving the ductility of molybdenum and tungsten are ascribed to three factors. First, the rhenium is said to form with oxygen a complex molybdenum-rhenium oxide which does not, like MOO,, give rise to a eutectic that wets the grain boundaries but tends to

be redistributed within the alloy grains. Secondly, the rhenium promotes twinning at room temperature and lowers the ductile-to- brittle transition temperature, thus improving low-temperature ductility. Finally, it is suggested that rhenium additions reduce the solubility of oxygen in molybdenum. This is said to be in accord with the theoretical predictions of D. A. Robins, who considers that the solubility of interstitial elements in Group VIA metals may be lowered by additions of higher group metals because of the tendency to maintain six bonding electrons. The addition of rhenium with seven electrons reduces the solubility of oxygen because the oxygen atoms tend to ionise and contribute electrons to the alloy. It is thought that the soluble oxygen atoms tend to lock dislocations, reducing low-temperature slip and influencing the yield point; so that, by reducing the oxygen content, the ductility is improved generally.

The influences of additions of the platinum group refractory metals to molybdenum, tungsten and chromium on these three factors have been examined in a very general way. The results may be summarised as follows:

(I) None of the platinum group elements appeared to have any significant effect in redistributing molybdenum oxide at the grain boundaries (osmium additions may have a very slight effect); and of other elements, those only which produced a real change in the oxide morphology were niobium and tantalum, added in amounts of 5 to 10 atomic per cent.

(2) Room temperature twinning in molybdenum, tungsten and chromium appears to be promoted by 5 to 7.5 atomic per cent of ruthenium or osmium and, to a lesser extent, by about the same amounts of the other platinum metals. The effect, for some unexplained reason, is more pronounced in cast than in annealed samples.

(3) The most interesting effect of noble metal additions was on the hardness of


cast molybdenum. Small additions, of the order of 0.1 atomic per cent of ruthenium, reduced the hardness from 170 to 140 V.H.N., this being ascribed to a reduction in the oxygen solubility. Similar additions of iridium, rhodium, osmium (and platinum) reduced the hardness to 145-150 V.H.N. There are indications that about I per cent of osmium reduces thc hardness of cast chromium. Larger additions of all the platinum metals increase the hardness of cast molybdenum, tungsten and chromium; no data are available on the effect of small additions to tungsten and chromium.

The work is by no means comprehensive or complete. An attempt to get a quick solution to the problem of finding a malleable complex molybdenum alloy was made by adding tantalum or niobium to redistribute the oxygen, together with small amounts of osmium, ruthenium, iridium or platinum to promote twinning and to reduce interstitial solubility, and small amounts of other de- oxidising elements (for luck) to supplement, it was hoped, all these effects.

The most successful molybdenum alloys contained the following additions, in atomic percentages:

(a) (b ) (4 (4 Ru 1.0 Ru 1.0 0 s 1.0 0 s 1.0 Si 0.1 Co 0.05 Ta 1.0 Ta 1.0

Si 0.1 Co 0.05 All these could be rolled directly to strip,

but when recrystallised they were brittle on bending, indicating no marked improvement in the ductile-to-brittle transformation.

It is considered by the authors that the most significant effect of these small additions of platinum metals is the reduced solubility for oxygen (and presumably of other interstitial impurity elements) through increase in the valence electron concentration. It may well be that further studies will prove that successful methods of producing industrially important alloys with the help of the refractory noble metals can be developed.

J. C. C.

The Hvdrides of Palladium J

and Palladium Alloys By F. A . Lewis, n . D . Chemistry Department, The Queen’s University of Belfast

I n the second part of this article, concluded from the October issue of ‘Platinum Metals Review’, a short account is given of changes in the ph.ysical properties of palladium following absorption of hydrogen. The behaviour of certain palladium alloys is compared with that of palladium and alternative methods of approach towards an understanding of the constitution of the hydrides are briefly outlined.

Specimens of hydrided palladium for which equilibrium with gaseous hydrogen is inhibited can remain either in vaciio or in air for long periods without appreciable loss of absorbed hydrogen (8): very many of the physical measurements on palladium hydrides have been carried out under such conditions (2). However, particularly in the presence of oxygen, the loss of hydrogen may be subject to erratic behaviour and once begun can sometimes proceed very rapidly indeed (8). Although it is usual that, on completion of physical measurements, an analysis of the final hydrogen content is obtained either by using strong oxidising solutions (8, 9, 33) or by degassing in vacuo (10, 34, 36), this alone will give no absolute indication of the content at the time of measurement.

It is thus important in these circumstances that convenient, reliable and non-destructive

physical measurements be developed to provide a continuous measurement of hydrogen content at all times.

Physical Properties of Palladium H ydrides

When compared to other solid systems the detailed measurement of physical properties as a function of hydrogen content is in principle especially convenient due to the ability of palladium to absorb large quantities of hydrogen without macro-disruption. How-

ever, although scattered measurements have been reported on a variety of properties such as elastic constants, hardness, Hall coefficient and thermoelectric power (2 , 29, 36, 37), the data available for most properties are generally not detailed over a wide range of hydrogen contents.

More complete studies have been made of changes in paramagnetism (12) which is found to decrease almost linearly with hydrogen content up to HjPd - 0.6, and particular attention has been paid to changes of electrical resistance.

The salient features of the changes of relative electrical resistance, R/R, (R, is the initial, hydrogen-free, resistance) with hydrogen Content (H/Pd, atomic ratio) at about 25°C are shown in Fig. 5. R/Ro increases almost linearly with H/Pd until H/Pd - 0.55 with a definite change of slope at the termi- nation of cr-phase(10, 12). Beyond HjPd- 0.55 there is enhanced disagreement between the results available (10) : R/R, is believed to decrease (12, 14, IS) when the content exceeds H/Pd - 0.7.

Although a somewhat larger variation has recently been suggested ( 3 9 , the R/R,-H/Pd relationships appear to be almost independent of temperature ( 3 4 , up to HjPd - 0.5, within the range o to 100°C.

For reasons discussed in the first p a t of this article, electrolysis has often been em-


ployed to introduce hydrogen for resistance studies, and it is unfortunate that sources of error (31) in the measurement of hydrogen content have not been fully appreciated in many of the earlier and most detailed studies of the R/R,- H/Pd relationships.

Errors in RjR,, can also result from proton transfer effects (38, 39) during the

1.8

1-6

0 LK

U \ 1.4

I 2

1.0

# - - 5 c .

I 9-10 Pt - Pd /

L I 1 1 I

01 0 2 0 3 0 4 0 5 0 6 0 7 0 8 application of the bridge (measuring) current in the H/M. (ATOMIC R A T I O )

relatively strong (I-2N) acid solutions which have generally Fig. 5 Relationships between relative electrical resistance and

been used as electrolyte and possible effects of absorbed oxygen (12, 40), which may be introduced during pre-annealing and activation of palladium must also be considered. Particularly since doubts that the removal of hydrogen is not always reflected by a change in R/Ro now appear to be largely unfounded ( IO), resistance changes fulfil, in principle, several of the necessary requirements of a continuous analytical measure of absorbed hydrogen.

Palladium Alloy -Hydrogen Systems

Little work has so far been reported on alloys of palladium with a metal such as titanium or vanadium that is also capable of absorbing large quantities of hydrogen.

The information available has been largely restricted to the behaviour of alloys with metals which, by themselves, absorb very little hydrogen such as the other metals of Group VIII or silver or gold. (Although such alloys may form ordered lattices in certain composition ranges after prolonged annealing (40), the samples which have so far been used have almost certainly been in the form of supercooled solid solutions).

The hydrides formed by these alloys again show no tendency for macro-disruption. Regions of coexistence of a- and p-phase hydrides are still found at close to room tem-

hydrogen content


perature for the lower contents of alloying metal (2). Properties such as electrical resistance are altered b y a similar order of magni- tude to those of palladium although with minor differences. For example, with increasing platinum content (Fig. 5 ) R/R, increases more steeply (34) with hydrogen content than for pure palladium, and increases less steeply in the case of silver-palladium alloys (12, 41, 42). As is shown in Fig. 5 the resistance may actually decrease slightly with increasing hydrogen content over the region of a- and p-phase coexistence for certain silver alloys (42), cf. Fig. 7.

Aside from somewhat more complex behaviour found with the silver-palladium, and almost certainly with gold-palladium alloys, which are further discussed below, the general effect of a feebly absorbing metal is to reduce the equilibrium amount of hydrogen absorbed by the alloy to below the amount absorbed by pure palladium, when comparison is made at almost any temperature and pressure.

Apart from some early study by Sieverts (43) of the Pt-Pd-H, Ag-Pd-H, and Au-Pd-H systems (at temperatures of 138°C and above and at pressures up to one atmosphere), virtually no P-C-T data have been obtained for palladium alloy-hydrogen systems by direct equilibration with molecular hydrogen in the

6 0 0

400

F 2 0 0

I \5

) oo c

12"/o Pt-Pd

,

I 6% P t - Pd / I / I

:roc 15.590 Pt - Pd

ul a 2 u)

2 6 0 0 a

400

200

0.2 0 4 0.6 0.2 0.4 0.6 H / M C (ATOMIC RATIO)

Fig. 6 Isotherms for a series of Pt- Pd- H systems

gas phase. For the bulk of the experimental work which has been carried out the hydrogen has been introduced into the alloys by electrolysis : since, until recently, electrode potentials were not generally measured in conjunction it is not surprising that there has been disagreement between the results obtained (12). There has been particular con- troversy with regard to the behaviour of the Ag-Pd-H system (12).

Certain of the difficulties appear to have been resolved by some further P-C-T data which has more recently been derived from electrode potential measurements. Although the electrochemical data have so far been obtained only over a rather narrow tern- perature range around 25T, it has been sufficient to indicate that the family of isotherms for each alloy that absorbs hydrogen have a similar general appearance to those of the Pd/H system (34, 44).

For the Pt-Pd-H system at 25 'C it has been found that increase of platinum content is paralleled by a steady increase in the eqaili- brium hydrogen vapour pressure over regions where cr and P-phase hydrides coexist (Fig. 6) . This reflects a corresponding decrease in


the chemical potential for the absorption of hydrogen, and by the use of the Clapeyron equation it has also been shown to reflect a decrease in the heat of absorption (4). In addition the P-C-T data indicates (Fig. 6 ) that the critical temperature and pressure for cc and @-phase coexistence is also steadily reduced with increase of the platinum content of the Pt-Pd alloys (34, 44).

The behaviour of the Ag- Pd-H system is, however, somewhat more complex. For example, with increase in silver content, at about 25"C, the ratio of hydrogen atoms to the total number of metal

atoms (H,'Me) in the P-phase hydrides (over the region of cr and P-phase coexistence) becomes progressively less than for pure palladium (H/Pd-o.r7). Nevertheless, again over the corresponding ranges of 01 and P- phase coexistence, the equilibrium vapour pressure steadily diminishes with increase in silver content up to about 30 per cent

As a result, although with increasing silver content at about 25°C the amount of hydrogen, absorbed under a pressure of one atmosphere, decreases continuously from the amount absorbed by pure palladium, more hydrogen is retained by the alloys with up to 30 per cent silver when the pressure is reduced to about 16mm. (Roughly the minimum vapour pressure for existence of the P-phase hydride of palladium at 25°C (42, 45).) It now seems clear that a consolidation of these data will give a complete thermodynamic justification for the experimental findings of Sieverts (43), that at higher temperatures ( 2 138°C) the amount of hydrogen absorbed by alloys with up to 30 per cent silver exceeds the amount absorbed by pure palladium, when compared at a pressure of one atmo-

(42, 45) (Fig. 7).

sphere. In view, for example, of the complex Ag-Pd-H behaviour, it is important not to overgeneralise when discus- sing these alloy-hydrogen systems. However, it seems that the minimum atomic percentage of feebly absorbing metal which has to be added to palladium so that the resultant alloy does not absorb hydrogen with the evolution of heat (exothermic absorpt ion) appears to be roughly correlated with oxidation number. For example, exothermic absorption appears to be unlikely

3

Q I 2 E E u

W 0 2 - 1

I l l / 40% Aq-Pd

P A L L A D I U M

I0 “1. A 9 - Pd c a 3 8 rnrn

c a 0.3 rnrn

2sDc

760mm

mrn

for alloys with >35 atomic per cent platinum (44) (the most common oxidation states of Pt are f 2 and -t4). The minimum percentage of nickel or rhodium (for which +2

oxidation states are common) that has to be added to produce a non-exothermally absorbing alloy is somewhat higher than 35 per cent (46, 47) and about 70 per cent of either gold (with oxidation states of +I and +3) or silver (with a common +I oxidation state) have to be added to palladium to achieve the same purpose (12~44). It has been suggested (44) that alloys which do not form p-phase hydrides within experimentally convenient pressure ranges at room temperature, but which can still exothermally absorb appreciable amounts of hydrogen in a-phase, may prove to have advantages over palladium for application as diffusion membranes.

Constitution of the Hydrides It appeared from the results of experiments

by Coehn and co-workers (12,41) that, under an electrical potential gradient, hydrogen was transferred from the positive to the negative pole of a specimen of palladium hydride. It was, therefore, concluded that the hydrogen was present in the solid in the form of protons.

These results could be conveniently incorporated into a simple picture of the Pd/H

0.1 0.2 0 3 0.4 0 . 5 0 6 0.7 0.8 H / M e (ATOMIC RATIO)

Fig. 7 Isotherms for Ag-Pd-H systems at 25°C


system in terms of the electron band theory of solids. For example, if the electrons lost by the hydrogen atoms were accepted into vacancies which exist in the ‘48 band of palladium, a plausible explanation could also be given of the seemingly linear decrease of the paramagnetic susceptibility of palladium up to HjPd N 0.55 ( ~ ~ 4 8 ) . As an extension of this picture it has been suggested that for HjPd > 0.55 the electrons donated by hydrogen could be incorporated into the ‘5s’ band of palladium (49).

As further support for this ‘free proton’ theory, a good matching of the experimental P-C-T data, including the region near to the critical temperature for CL and P-phase coexistence, was obtained by a statistical thermodynamic analysis (49) which considered the interaction energy between the protons as a function of their concentration.

On the other hand, Coehn’s interpretations of his experimental results have not gone unchallenged (39), and it may be claimed that similar changes of magnetic properties would result from other more usual forms of chemical union (37). It has also been pointed out that the ‘free proton’ theory has not allowed for any alteration of the electron bands of palladium which should result from the interatomic expansion when $-phase hydride is formed (50).

Since a system of resonating hydrogen resistance of palladium to disruption by bridge bonds has been suggested to account for certain features of uranium hydrides, this has helped to encourage a proposal (3) that the chemical binding in the Pd/H system may he of a more covalent type at temperatures below 0°C. Although the covalent model is advanced (3) as being complementary to the free proton model at higher temperatures a A type specific heat anomaly observed at around 70°K has been suggested (3) to indicate local ordering to covalently bonded molecular units with a formula PdH,. It is of interest to note that marked electrical resistance changes have also recently been reported (37) over the same temperature range as the specific heat anomaly.

An approach more diametrically opposed to the free proton theory is to consider the p-phase hydrides as ionic structures in which the hydrogen is present as negative ions. Some attention to this approach seems warranted if for no other reason than to examine any possible correlation between the hydrides of palladium and its alloys and other broad groups of solids.

Pressure-concentration isotherms of many chemical systems, including a number which comprise a transition metal and a more

hydrogen. It does appear, however, that the similarities of features such as the P-C-T data and electrical properties to those of the remainder of the transition metal hydrides may be at least as important a consideration. I t is thus of interest to note that interatomic distances in several transition metal hydrides are compatible with the hydrogen being present as negative ions (53, 54, 55).

References 36 F. A. Lewis, G. E. Roberts and A. R.

Ubbelohde, Proc. Roy. SOC., 1953, 2mA, 279

37 A. I. Schindler, R. J. Smith and E. W. Kammer, Tenth Int. Congress on Refrig- eration: Copenhagen, r959

38 A. W. Carson, T. B. Flanagan and F. A. Lewis, Naturwiss., 1959, 46,374, and Trans. Faraday SOC., 1960,56, 1311, 1324

39 C. A. Rnorr and E. Schwartz, Z. Elektrochem.,

40 E. Raub, J . Less Common Metals, 1959, I, 3 41 A. Coehn and H. Jurgens, Z. Physik, 1931,

71, I79 42 F. A. Lewis and W. H. Schurter, Naturwiss,

19% 47, I77 43 A. Sieverts, E. Jurisch and A. Metz, Z. anorg.

Chem., 1915, 92, 329 44 A. W. Carson, T. B. Flanagan and F. A.

Lewis, Nature, 19.59, 183, 39, 510, and Trans. Faraday SOC., 1960, 56, 1332

1933, 39,281; iKd., 1934,40, 37

electronegative element such as oxygen and suluhur, show similarities with the Pd/H iso-

45 Z. L. Vert and I. P. Tverdovskii, Zhur. Fiz. Khim., 1954, 28, 317 -~

therms (sI). The solid phases of these systems are likewise found to show marked divergence from stoichiometry and to exhibit

46 I. P. Tverdovskii and A. I. Stetsenko, Doklady Akad. Nauk S.S.S.R., 1952, 84, 997

47 I. P. Tverdovskii and Z. L. Vert, Doklady Akad. Nauk S.S.S.R., 1953, 88, 305

considerable electronic conductance. Although 48 N. F. Matt and H. Jones, Theory of the detailed explanations are often complex, such Properties of Metals and Alloys: Oxford

University Press, 1936, p. 316 behaviour is generally dealt with in terms of

49 J. R. Lacher, Proc. Roy. SOC., 1937, 16rA, 525 lattice vacancies or interstitial species in a 50 A. R. Ubbelohde, Proc. Roy. SOC., 1937, reference stoichiometric crystal (51). There 159A, 295; cf. also A. Harashima, T. Tanaka appears to be an increasing amount of evidence and K. Sakaoku,?. Phys. SOC. Japan, 1948,

3,208 that the hydrides of other transition and rare 51 See, for example, A. L. G. Rees, Chemistry

earth metals can be included in this general of the Defect Solid State, Methuen: London, 1954 group (52).

The PdiH system has generally been somewhat set apart, even from the other ‘exothermic’ transition metal hydrides. This seems due both to the apparent success of the

52 E. J. Goon,?. Phys. Chem., 1959, 63, 2018 53 G. G. Libowitz and T. R. P. Gibb, 3. Phys.

54 T. R. P. Gibb, in course of publication 55 G. G. Libowitz, J . Nuclear Materials, 1960,

Chem., 1956, 60, 510

‘proton gas’ model and to the superior 2, 1


Faraday’s Lecture on Platinum THE CENTENARY OF A CLASSIC

In the course of his long researches Michael Faraday more than once turned his attention to platinum and its properties, and on February 22nd 1861-when i n his 71st year-he delicered his famous ‘Lecture on Platinum’ to the members of the Royal Institution. A n abridged version of this address is reprinted here for the historical interest it inill undoubtedly haw for the metallurgist of today and f o r the picture it conveys of a great but modest scientist

When I was tempted to propose this subject for your attention this evening, it was founded upon a promise, and a full intent of perform- ing that promise, on the part of my friend Deville, of Paris, to come here to show before you a phenomenon in metallurgic chemistry not common. In that I have been disappointed. His intention was to have fused here some thirty or forty pounds of platinum, and so to have made manifest, through my mouth and my statement, the principles of a new process in metallurgy in relation to this beautiful, magnificent, and valuable metal; but circumstances over which neither he nor I, nor others concerned, have sufficient control, have prevented the fulfilment of that intention, and the period at which I learned the fact was so recent, that I could hardly leave my place here to be filled by another, or permit you, who in your kindness have come to hear what might be said, to remain unreceived in the best manner possible to me under the ur- cumstances. I therefore propose to state as well as I can what the principles are on which M. Deville proceeds by means of drawings, and some subordinate or inferior experiments.

The metal platinum, of which you see some very fine specimens on the table, has been known to us about a hundred years. It has been wrought in a beautiful way in this country, in France, and elsewhere, and supplied to the consumer in ingots of this kind, or in plates, such as we have here, or in masses, that by their very fall upon the table

indicate the great weight of the substance, which is, indeed, nearly at the head of all substances in that respect. This substance has been given to us hitherto mainly through the philosophy of Dr. Wollaston, whom many of us know, and it is obtained in great purity and beauty, It is a very remarkable metal in many points, besides its known special uses.

Now, with regard to this substance, let me tell you briefly how we get it. The process used to be this. The ore was taken, and digested in nitro-muriatic acid of a certain strength, and partly converted into a solution, with the leaving behind of certain bodies.

The platinum being dissolved with care in acids, to the solution the muriate of ammonia was added, as I am about to add it here. A yellow precipitate was then thrown down, as you perceive is the case now; and this, carefully washed and cleansed, gave us that body [pointing to a specimen of the chloride of platinum and ammonium], the other elements, or nearly all, being ejected. This substance being heated, gave us what we call platinum sponge, or platinum in the metallic state, so finely divided as to form a kind of heavy mass or sponge, which, at the time that Dr. Wollaston first sent it forth, was not fusible for the market or in the manufacturers’ work- shops, inasmuch as the temperature required was so high, and there were no furnaces that could bring the mass into a globule, and cause the parts to adhere together. These divided grains of spongy platinum having been

Platinum Metals Rev., 1961, 5, (1),26-29 26

well washed and sunk in water for the purpose of excluding air, and pressed together, and heated, and hammered, and pressed again, until they come into a pretty close, dense, compact mass, did so cohere, that when the mass was put into the furnace of charcoal, and raised to a high temperature, the particles, at first, infinitely divided-for they were chemically divided-adhered the one to the other, each to all the rest, until they made that kind of substance which you see here, which will bear rolling and expansion of every kind. No other process than that has hitherto been adopted for the purpose of obtaining this substance from the particles by solution, pre- cipitation, ignition, and welding.

This is the process adopted by Messrs. Johnson and Matthey, to whose great kindness I am indebted for these ingots and for the valuable assistance I have received in the illustrations.

The treatment, however, that I have to

bring before you is of another kind, and it is in the hope that we shall be able before long to have such a thing as the manufacture of platinum of this kind that I am encouraged to come before you, and tell you how far Deville has gone in the matter, and to give you illustrations of the principles on which he proceeds.

Deville’s process depends upon three points-upon intense heat, blowpipe action, and the volatility of certain metals. We know that there are plenty of metals that are volatile, but this, I think, is the first time that it has been proposed to use the volatility of certain metals, such as gold and palladium, for the purpose of driving them off and leaving something else behind. He counts largely upon the volatility of metals which we have not been in the habit of considering volatile, but which we have rather looked upon as fixed.

Let me now tell you briefly what Deville proposes to do. First of all, he takes this ore

Faraday deliuering a lecture at the Royal Institution. The illustration, from a painting by Blaikley in the possession of the Royal Institution, shows him giving the jirst of a series of lectures on ‘Metals’ in 1855. In the centre of the front row is the Prince Consort with his sons the Prinre of Wales (afterwards

King Edward YYl) and Prinrs Alfred on either side


with its impurities and mixes it (as he finds it essential and best) with its own weight of sulphuret of lead-lead combined with sulphur. Both the lead and the sulphur are wanted; for the iron thar is there present, as you see by the table, is one of the most annoy- ing substances in the treatment that you can imagine, because it is not volatile; and while the iron remains adhering to the platinum, the platinum will not flow readily. I t cannot be sent away by a high temperature-sent into the atmosphere so as to leave the platinum behind. Well, then, a hundred parts of ore and a hundred parts of sulphuret of lead, with about fifty parts of metallic lead, being all mingled together in a crucible, the sulphur of the sulphuret takes the iron, the copper, and some of the other metals and impurities, and combines with them to form a slag; and as it goes on boiling and oxidising, it carries off the iron, and so a great cleansing takes place.

Now you ought to know that these metals, such as platinum, iridium, and palladium, have a strong affinity for such metals as lead and tin, and upon this a great deal depends. Very much depends upon the platinum throw- ing out its impurities of iron and so forth by being taken up with the lead present in it.

When he (Deville) has melted these substances and stirred them up well, and so obtained a complete mixture, he throws in air upon the surface to burn off all the sulphur from the remaining sulphuret of lead; and at last he gets an ingot of lead together with platinum-much lead comparatively, and little platinum.

He gets that in the crucible with a lot of scorias and other things, which he treats afterwards. It is that platiniferous lead which we have to deal with in our future process. Now let me tell you what he does with it. His first object is to get rid of the lead. He has thrown out all the iron, and a number of other things, and he has got this kind of compound. He may get it as high as 78 per cent. of platinum, and 22 of lead; or 5, or 10, or 15 of platinum, and 95, or 90, or 85 of lead

(which he calls weak platinum), and he then places it in the kind of vessel that you see before you. The combustible metal-that is, the lead-and the part that will oxidise, are thoroughly oxidised; the litharge flows out in a fused state into a vessel placed to receive it, and the platinum remains behind.

Removing the Eitharge in a fused state from the surface of the molten platinum

Here is the process which Deville adopts for the purpose of casting off the lead after he has got out the platinum from the ore. (Having made use of your friend, you get rid of him as quickly as you can.) He gets his heat by applying the combination of oxygen and hydrogen, or of carburetted fuel, for the purpose of producing a fire. Having obtained heat like this, the next consideration is, what vessel is he to employ which could retain the platinum when so heated, or bear the effects of the flame? Such vessels are happily well supplied at Paris, and arc formed of a substance which surrounds Paris; it is a kind of chalk (called, I believe, by geologists calcaire gross&), and it has the property of enduring an extreme degree of heat.

I am now going to get the highest heat that we can obtain. First, I show you the combustion of hydrogen by itself. If I put a piece of lime obtained from this chalk into the gas, you see we get a pretty hot flame which would burn one’s fmgers a good deal. But now let me subject a piece of it to the joint action of oxygen and hydrogen. I do this for the purpose of showing you the value of lime as a material for the furnaces and chambers that are to contain the substances to be operated on, and that are consequently


to sustain the action of this extreme heat. I have two or three rough drawings here

representing the kind of furnace which Deville employs. It is made of a piece of lime below and a piece of lime above. You see how beautifully lime sustains heat without altering in shape; and you may have thought how beautifully it prevents the dissipation of the heat by its very bad conducting powers. While the front part of the lime which you saw here was so highly ignited, I could at any moment touch the back of it without feeling

The lime-blork furnare designed by Deville

any annoyance from the heat. So, by having a chamber of lime of this sort, he is able to get a vessel to containthese metals with scarcely any loss of heat. He puts the blow-pipes through these apertures and sends down these gases upon the metals, which are gradually melted. He then puts in more metal through a hole at the top. The results of the combustion issue out of the aperture which you see represented. If there be strips of platinum he pushes them through the mouth out of which the heated current is coming, and there they get red-hot and white-hot before they get into the bath of platinum. So he is able to fuse a large body of platinum in this very manner.

When the platinum is melted he takes off the top and pours out from the bottom piece, like a crucible, and makes his cast. This is the furnace by which he fuses his forty pounds or fifty pounds of platinum at once. The metal


is raised to a heat that no eye can bear. There is no light and shadow, no chiaroscuro there; all is the same intensity of glow: you look in and you cannot see where the metal or the lime is; it is all as one. We have, therefore, a platform with a handle, which turns upon an axis, that coincides with the gutter that is formed for the pouring of the metal; and when all is known to be ready, by means of dark glasses, the workmen take off the top piece and lift up the handle, and the mould being then placed in a proper position, he knows that the issue of the metal will be exactly in the line of the axis.

I have said that Deville depends upon intense heat for carrying off vapour and proposes to throw out in this way all those extraneous things except two, namely iridium and rhodium. It so happens that iridium and rhodium do make the metal more capable of resisting the attacks of acids than platinum itself. Alloys are compounded up to 25 per cent of rhodium and iridium by which the chemical inaction of the platinum is increased and also its malleability and other physical properties.

I have now finished this imperfect account. It is but an apology for not having brought the process itself before you. I have done the best I could under the circumstances, and I know your kindness well, for if I were not aware that I might trust to it, I would not appear here so often as I have done. The gradual loss of memory and of my other facul- ties is making itself painfully evident t Q me, and requires, every time I appear before you, the continued remembrance of your kindness to enable me to get through my task. If I should happen to go on too long, or should fail in doing what you might desire, remember it is yourselves who are chargeable by wishing me to remain. I have desired to retire, as I think every man ought to do before his facul- ties become impaired; but I must confess that the affection I have for this place, and for those who frequent this place, is such that I hardly know when the proper time has arrived.

ABSTRACTS of current literature on the platinum metals and their alloys

PROPERTIES Tensile Properties of the Platinum Group Metals F. c. HOLDEN, R. w. DOUGLASS and R. I. JAFFEE, Paper presented at the Third Pacific Area Na- tional Meeting, A.S.T.M., San Francisco, Oct. 1959. A.S.T.M. Special Technical Publication No. 272. Tests were carried out in the temperature range -196" to IOOO"C on Ru, Rh, Pd, Ir and Pt, all in the annealed condition. With the exception of Pd, material representing different grades of purity or methods of fabrication were used for each metal. Ru was prepared by powder metallurgy techniques; Rh, Pd, Ir and Pt were obtained as rod or wire; electron-beam melted Rh and Ir also were tested. Ru showed rather low ductility at 750"~ IOOOO and IZOO"~ and a tensile strength of 31,400 psi at 1000°C. Throughout the range -196" to IOOO'C, Rh showed good ductility, and

at IOOO~C, a tensile strength of about 12,500 psi. Pd, over the whole temperature range, showed low strength and high ductility. Tensile strengths of Ir decreased with increasing temperature to about 45,000 psi at rooo"C; ductility was good at higher temperatures, but low up to SOOT. Pt resembled Pd with high ductility and low tensile strength. Twinning was observed in all five metals. Strengths plotted a. homologous temperature indicate that Rh, Ir and Ru are stronger than Pd and Pt.

Iron-Ruthenium Alloys E. RAUB and W. PLATE, Z . Metallkunde, 1960, 51, (81,477-481 A series of Fe-Ru alloys were investigated in the temperature range 400"-1300"c by X-ray and dilatometer methods, and microscopy. Earlier reports on the stabilisatjon of y-Fe by Ru were confirmed. The y-cx and y-c transformations and their influence on the thermal expansion curves were studied for various alloys up to 30 at. 94, Ru. The crystal structure of the alloys after heat treatment at various temperatures is given in some detail.

The System Iridium-Tellurium E. P. HOCKINGS and J. G. WHITE, 7. Phys. Chem.,

Specimens, obtained by heating I r powder and T e in vacuo, were examined by X-ray powder diffraction methods. Two compounds, IrTe, and IrsTes, were observed and their crystal structures were determined. IrTe, has the (C6)

1960, 64, (8), 1042-1045

type structure and Ir,Te, has a defect (CZ) type structure with approximately one-quarter of the cation sites vacant. The structures are discussed in relation to the arrangement of the electronic energy levels of the metal atoms.

Absorption of Hydrogen by Palladium/ Platinum Alloys. Part 3. Some Thermo- dynamic Factors A. w. CARSON, T. B. FLANAGAN and F. A. LEWIS, Trans. Faraduy SOL., 1960, 56, (9), 1332-1339

Electrode potential measurements were made on a series of Pt-Pd alloys over a temperature range 0"-59"C and free energies of solution of hydrogen and hydride vapour pressures were derived as a function of the hydrogen content. Entropies and partial molar heats of formation of P-phase hydrides were derived for alloys containg 2.79, 5.73 and 8.80 at.:: Pt. It is suggested that hydrogen absorption in alloys with greater than 35 at.:; hydrogen is unlikely to be exothermic. Results indicate that, with increasing Pt content, the critical temperature and pressure for x-p phase coexistence decreases.

Low Temperature Dependence of the Elec- trical Resistivity and Thermoelectric Power of Palladium and Palladium-Nickel Alloys Containing Absorbed Hydrogen A. I. SCHINDLER, R. J. SMITH and E. w. KAMMER, U.S. Naval Research Laboratory Report 5481,

Measurements of electrical resistivity and thermoelectric power were made on wires of Pd, IoO,, Ni-Pd and 1774 Ni-Pd containing various amounts of absorbed hydrogen. At T=50°K, a resistivity maximum and, relative to pure Pd, a thermoelectric power minimum were found for samples with H/Pd>o.58. These samples also showed a resistivity minimum at approximately 9o'K. The absolute thermoelectric power for Pd-H decreases rapidly as a function of composition in the region HjPd 0.6 at temperatures

85"K, while above 95°K a maximum is shown at H/Pd-o.6.

On the Contamination of Platinum with Fission Products and the Decontamination of Contaminated Platinum with Acids T. YANAGIIIARA, H. KIMURA and M. CHIBA, J. Jap. Inst. Metals, 1960, 24, (7), 413-417 (English summary) Pt plates were soaked in a solution of fission products and maximum contamination was

196% Jun. 3,6 PP.


reached in about 3 hours. It was shown by autoradiography, electron microscopy and optical microscopy that the contamination is affected by the surface condition of the Pt. The plates were decontaminated with tap water, HC1, HNO,, H,SO,, H,PO,, HF and fused salts. Of those investigated hot HC1 and fused KHSO, were the most effective decontaminating agents. The degree of contamination of Pt with fission products is very low.

Mass-Spectrometric Study of the Osmium- Oxygen System R. T. GRIMLEY, R. P. BURNS and M. G. INGHRAM, J. Chem. Phys., 1960, 33, (I), 308-309 The main ionic species produced from a Knudsen cell in the temperature range I 1oo-175o"K were OsO,+ and OsO,'. The ratio OsO,+:OsO,+ is a function of the oxygen pressure and the temperature and confirms the presence of OsO, and OsO, molecules in the vapour phase. Above 1700°K, evidence supports the existence of a stable OsO, molecule.

Equilibrium Measurements in the Iridium- Oxygen System. Gaseous Iridium Trioxide

Chem., 1960, 304, (5/6), 249-265 Measurements made by the carrier gas method have shown that Ir and IrO, heated in currents of oxygen or oxygen-nitrogen are volatilised with the formation of gaseous Ir03, which is stable up to 1700°C. This confirms previous hot wire experiments. The interpretation of published hot wire experiments with Pt and Rh indicates the existence of Pt,O, and Rh,O,. Thermo- dynamic data for IrO&) and IrO&) have been obtained.

Equilibrium Measurements in the Platinum- Oxygen System. Gaseous Platinum Dioxide H. SCHAFER and A. TEBEEN, Z. Anorg. Allgem. Chem.

Pt was volatilised as the dioxide by heating in an oxygen atmosphere. The equilibrium Pt+ O,= PtO&) was measured in the range I 107"-1208'C and the following data were obtained: AH,,,== 41.30 kcal; AS2,,-3.o1 cl; S(PtO,(,), 298)= 62.0 cl.

H. SCHAFER and H. J. HEITLAND, z. Anorg. Allgem.

1960, 304, (5/6), 317-321

Changes in Resistance on the Chemisorption of Gases on Thin Metal Films w. M. H. SACHTLER and G. J. H. DORGELO, 2. Phys. Chem. (Frankfurt), 1960, 25, (I/?,), 69-74 The Pt-H system was investigated. It was found that, as with other metals, chemisorption of hydrogen effects a sharp initial increase in the electrical resistance of the films. Absorption of hydrogen in the metal lattice often causes a decrease in resistance. A temperature as low as -21oOC is necessary for suppressing the absorption of hydrogen in Pt.

Kinetics of Hydrogen and Oxygen Adsorp- tion and Their Reaction on Platinum P. K. MIGAL' and v. A. TSIPLYAKOVA, Zhur. Fiz. Khim., 1960, 34, (6), 1153-1160 (English summary) The adsorption of hydrogen and oxygen and their interaction in the presence of As, Hg and of (CN)' ions were investigated. The adsorption rate for hydrogen on non-poisoned Pt was found to be of zero order. The effect of the poisons on the hydrogen adsorption rate diminishes in intensity in the order (CN)'>Hg>As. I t is suggested that the reaction between adsorbed hydrogen and molecular oxygen takes place according to the "impact" mechanism with redistribution of hydrogen on the surface. A similar mechanism without surface redistribution of oxygen is suggested for the reaction between adsorbed oxygen and molecular hydrogen. The effect of As, Hg, and (CN)' ions on the reaction rates was studied.

Modern Industrial Uses of the Platinum Metals w. BETTERIDGE and D. w. RHYS, Metal Industry, 1960, 97, (9, 10 and 11), 163-166, 183-185 and

The physical and chemical properties of the Pt metals upon which many of their applications depend are given. Major uses of the metals in the metallurgical, chemical, petroleum, electrical, glass, synthetic fibre and atomic energy industries are reviewed.

203-205

The Thermal and Magnetic Properties of Some Transition Element Alloys D. w. BUDWORTH, F. E. HOARE and J. PRESTON, Proc. Roy. SOC., Series A, 1960, 257, (1289), 250-262 Magnetic measurements were made on 40 different Pd-Rh, Pt-Ir and Pt-Au alloys. The specific heats of Pd-Rh and Pt-Au alloys and the pure metals Rh, Pt and Au were measured in the range 1.8 to 4.2"K and the electronic heats and Debye temperatures were computed. Tables of results are given. Similarities between alloys of Pd and Ag or Rh with alloys of Pt and Au or Ir are noted.

Magnetic Properties of the Pd and Pt Group Transition Metal Complexes H. KAMIMURA, s. KOIDE, H. SEKIYAMA and s. SUGANO, 3. Phys. soc. Japan, 1960, 15, (7),

Magnetic susceptibilities and g-values are calcu- lated by means of the intermediate coupling scheme. The effect of the dy orbitals is neglected because of the cubic symmetry of the crystalline field. The effect of the Coulomb repulsion is regarded as comparable to that of the spin-orbit interaction. The results are compared with experimental data.

1264-1272


Vapour Pressures of Platinum Metals. I. Palladium and Platinum L. H. DREGER and J. I. MARGRAVE, 3. Phys. Chem., 1960, 64, (91, 1323-1324 Vaporisation studies were carried out by the Langmuir free evaporation technique. Results obtained for Pt are: log Pmso1id=1o.362- 29,1oo/T; AH",,,: 135.2 fo.8 kcal/mole; estimated boiling point%4100i 100°K. For Pd: log P,,solid=9.075-19,425/T; A H 0 2 9 8 = 9 ~ . ~ fo.8 kcal/mole; estimated boiling point w 3200% 100°K.

Investigation of Adsorption on Platinised Carbon by Change of the Gaseous Atmosphere A. N. MOSEVICH, B. P. NIKOL'SKII, v. I. PARAMONOVA and E. L. MORDBERG, Zhur. Phys. Khim., 1960, 34, (9), 1900-1906 (English summary) The adsorption of Cs and Br ions from aqueous solutions in hydrogen and air atmospheres was investigated. Adsorption and desorption studies were carried out both in the presence and absence of a buffer and of foreign ions. The adsorption of Cs and Br ions was shown to have an electro- static character and to conform to the basic laws of ion exchange.

Increasing the Stability of the Passive State in Titanium N. D. TOMASHOV, G . P. TSHCHERNOVA and R. M. ALTOWSKI, 2. Phys. chem. (Leipzig), 1960, 214,

The behaviour of Ti and its alloys with 1% and 2% of Pt and Pd on cathodic and anodic polarisation in H,SO, and HCl solutions was studied by potentiostatic methods. It was shown that the complete passivation of T i is made more difficult by increasing the temperature and concentration of the acid solution. The alloys of Ti with Pt and Pd have a substantially higher corrosion stability than Ti. T i may be protected anodically in H,SO, and HC1 of all concentrations and may be passivated by cathodic depolarisers such as ions of Pt", Cu2+ and Fe3f in the corrosive medium.

(5/6), 312-323

Some Aspects of the Structural Chemistry of Platinum E. G. cox, J . Roy. Znst. Chem., 1960, 84, (Aug.),

The historical development of the study of the stereochemistry of Pt co-ordination compounds is outlined. The structure of derivatives of Pt(CH,),I is discussed.

The Melting Point of Osmium A. G . KNAPTON, J. SAVILL and R. SIDDALL, J. Less- Common Metals, 1960, 2, (9, 357-359 The melting point was redetermined as 3 0 4 5 i 30% by direct measurement of the black-body radiation from a hole near the centre of an electrically heated bar.

283-284

Miscibility Curves and Critical Point of the Gold-Platinum System A. M~~NSTER and K. SAGEL, Z , Phys. Chem. (Frank-

Miscibility curves and the critical point of the system were determined by measurement of electrical conductivity. The critical temperature, tk, is given as 1agz*1.5"C and the critical atomic fraction of Pt, Xk, is 0.40fo.007. The results of a study of the shape of the miscibility curves were compared with the Fuchs theory of lattice models.

furt), 196% 23, (5/6), 415-425

Nitrides of Iron with Nickel, Palladium, and Platinum H. H. STADELMAIER and A. c. FRAKER, Trans. Met. SOC. A.Z.M.E., 1960, 218, (3), 571-572 Nitrides were prepared as powders and their crystal structure was derermined with a powder camera. A perovskite structure is assumed for Fe,PdN with Pd and the interstitial nitrogen fully ordered.

New High-Coercivity Alloys in the Binary Systems Fe-Pt, Fe-Pd and Ni-Pd z. I. ALIZADE, Bull. Acad. Sci. U.S.S.R., Phys. Series, 1959, 23, (3), 399-400 (Izvest. Akad. Nauk S.S.S.R., Ser.fiz., 1959, 23, (3), 416-417) The magnetostriction of alloys with a wide range of Pt and Pd concentrations was investigated. Results obtained for the three systems of the relationship between saturation magnetostriction and alloy composition are shown graphically. Fe-Pt and Fe-Pd alloys have a positive maximum saturation magnetostriction. The Ni-Pd system, however, comprises a number of alloys with a high negative magnetostriction.

Elastic Constants of Palladium from 4.2 to 500°K J. A. RAYNE, Phys. Rev. Letters, 1960, 4, (8), 437-438 Extrapolation to absolute zero of the data obtained on a single crystal gives the following results: c , , = ( ~ . ~ ~ I & o . o z ~ ) x rola dyne cm-', cI2= (1.761 k0.027) x roI2 dyne cm-', cd4=(o.712& 0.003) x 10'~ dyne an-'.

Research on the Alloys of Noble Metals with the More Electropositive Elements. 111. Micrographic and X-Ray Examination of Some Magnesium-Platinum Alloys R. FERRO and G. RAMBALDI, J . Less-Common

Alloys in the range 0-30 at.% Pt were prepared and examined by chemical analysis, specific gravity determination, micrographic and X-ray examination. The eutectic composition and temperature were estimated to be about 7.5-7.6 at.% Pt and 575"C, respectively. Intermediary <- and &phases were detected. The &phase,

Metals, 1960, 2, (s), 383-391


corresponding to Mg,Pt, is face-centred cubic and the &phase, corresponding to MgsPt, is hexagonal Na,As type.

ELECTROCHEMISTRY Proton Transfer between PdiH and Pd/Pt/H Electrodes Part 1. Equilibrium Hydrogen Electrodes A. w. CARSON, T. B. FLANAGAN and F. A. LEWIS, Trans. Furaduy SOC., 1960, 56, (9), 1311-1323 The investigation was carried out in IN HC1 without evolution of hydrogen using continuous and separated wire electrodes of Pd and Pt-Pd alloys containing 2.79, 5.73, 8.80 and 12.03 at.o; Pt. It was found that polarisation of proton transfer is relatcd to imposed changes of the hydrogen content of the electrodes. The activation energy for proton transfer was determined as 4.9 kcal/mole. The effect of proton transfer in solution upon electrical resistance measurements was studied.

Part 2. Incomplete Polarisation of Proton Transfer Ibid., 1324-1328 Studies on specimens as above showed that when the hydrogen content of the electrodes corres- ponds to the coexistence of dc- and $phases, reversible concentration polarisation of proton transfer may be incomplete. Effects of the incomplete polarisation on the measurement of electrical resistance in acidic solutions were observed for the series of Pt-Pd alloys and reasons for errors are discussed.

A Study of the Adsorption Phenomena of Rhodium, Iridium, Pallarlium and Gold with the Potentiostatic Triangle Method F. G. WILL and c. A. KNORR, Z. Elektrochem., 1960.

The adsorption of hydrogen and oxygen on the precious metals was studied. It was found that the maximum hydrogen coverage of the roughened surface was 6z00 for Rh, 45q4 for Ir, and 3076 for Au. The surface coverage is dependent on the potential velocity and preliminary treatment, For each metal oxygen evolution and layer- formation commences at a different value of potent@. With the exception of Ir, in the range investigated oxygen layer-formation increases up to 2.2V. Some characteristic measurements for each precious metal studied are given in a table.

The Determination of Diffusion Coefficients DH,, DH+ and DOH- with a Platinum Disc Electrode

64, (2)) 270-275

M. BREITER and K. HOFFMANN, z. Elektrochem., 1960, 64, (41, 462-467 The apparatus with the Pt disc electrode is described. The diffusion coefficients were determined by means of the Lewitsch formula from


measurements of anodic or cathodic limiting current densities. DH, was measured in o.5N H,SO,, 5N H$O, and o.rM Na,SO, in the temperature range -10' to 60°C from the anodic limiting current density of hydrogen molecules. DH+ was obtained in weakly acid O.IM Na,SO, at 20°C from the cathodic limiting current density of H- ions and DOH- was obtained in weakly alkaline 0.1 M Na,SO, from the anodic OH- ion limiting current density.

The Electrolytic Formation and Dissolution of Oxide Films on Platinum H. A. LAITINEN and C. G. E N K E , ~ . Electrochem. soc., 1960, 107, (911 773-731 An electrolytic cell consisting of a Pt foil indi- cator electrode, a Pt gauze counter electrode and HC10, electrolytes of varying strengths was used in conjunction with a calomel reference electrode. The formation of surface PtO was believed to be an irreversible reaction due to a mechanism which involves a hydroxyl radical intermediate. It was concluded that the steady-state cvolution occurs on a surface which has at least one atom of oxygen per surface Pt atom. A first order reduction of the surface oxide was shown experimentally. The surface oxide is reduced at potentials several hundred mV cathodic to the oxide formation potential and the rate of dissolution increases with increasing cathodic electrode potential.

Catalytic Activity and Electronic Structure of Rhodium-Palladium-Hydrogen Cathodes in Acid Solution J. P. HOARE, J. Electrochem. SOC., 1960, 107, (IO), 820-825 Hydrogen overvoltage measurements were made on Rh-Pd cathode beads containing I, 2, 5, 10, 15, 20, 50 and 90 at.o/, Rh hydrogen stirred in 2N H,SO, at 25°C. u- and $-phases, similar to those existing in the Pd-H system, were investigated. The mechanisms of the reactions on the various cathodes are discussed. The catalytic activity of the cathode surface for the hydrogen reaction was determined at low current densities. It is suggested that vacancies in the d-band of the cathodes make possible the strong chemical bonds between the absorbed hydrogen and the surface and that there is a direct relationship between the heat of absorption of hydrogen and the catalytic activity. The density of states at the Fermi level determines rhe strength of the bonds.

Electrochemical Phenomenon at the Glass- Refractory Material Interface L. LEGER, M. BOFFE and E. PLUMAT, Glass Technol.,

Measurements of the e.m.f. developed at the glass-refractory contact served to record continuously alkali penetration of the refractory and

1960, 1, (4), 174-179

to study the kinetics of the refractory attack by the molten glass. Solid-solid, solid-liquid, and liquid-liquid systems were investigated and in each case, Pt connecting plates or wires were used. The influence of the atmosphere was studied by introducing different atmospheres around two Pt wire electrodes dipping in molten glass. Both static and dynamic tests were carried out and the experimental procedures are described in detail.

Hydrogen Evolution on Platinum Elec- trodes. The Heats of Activation for the Component Reactions R. PARSONS, Trans, Faraduy Sac., 1960, 56, (9), 1340-1350 Measurements were made at various tempcratures in o.5M HCI of steady-state current-voltage curves in the range 4 x 10-’ to 10 Acm-2 using a Pt sphere electrode. The heat of activation at the reversible potential was found from the polarisation curves to be 5.2 kcal. The impedance of the electrode was measured as a function of frequency and temperature. It is estimated that the exchange cu+rent of the discharge reaction is more than IOO times that of the overall reaction, but the heat of activation is approximately the same.

Investigation of Surface Changes of a Platinum Electrode H. GRUBITSCH and K. HECKEL, Werkstoffe u. Korrosion, 1960, I I, ( 5 ) , 271-273 The surface changes of a polished electrode, used as a cathode in the galvanic cell -Cd 1 O.IN NaCllI O.IN NaC1, air I Pt I-, were investigated by electron microscopy. The circuit was alternately completed and broken every 15 mins. Observed changes in the surface of the Pt electrode apparently correspond to a recon- struction of the surface and to a lessening of its activity. This decrease in surface activity explains the slow current decrease with ventilating elements, the cathodes of which are immersed in an electrolyte with constant oxygen content.

ELECTRODEPOSITION Peculiarities of Cathodic Reduction of Platinum Metals from Complex Electrolytes A. I. LEVIN and B. A. FANKRATOV, J . Appl. Chem. U.S.S.R., 1959, 32, (8), 1825-1831 (Transl. of Zhur. Priklud. Khim., 1959, 32, (8), 1787-1793) Shifts of potential in absence of current in various electrolytes containing Pt metals were investigated. The potentials depend on the salt content and concentration of the electrolyte and shift in the negative direction with increasing dilution. Electrode polarisation accompanying simultaneous discharge of Pt metals from complex mother liquors was studied. It was found that

this polarisation is diminished in thc presence of Cu in the electrolyte due to the simultaneous discharge o f the Cu cations with the Pt metals.

LABORATORY APPARATUS AND TECHNIQUE Compact Palladium Diffusion Leak for Hydrogen

Instr., 1960, 31, (7), 789-790 A Pd thimble (2 in. diameter, 0.005 in. wall thickncss) is brazed to an inner Heliarc ring which is brazed to a stacked ceramic arrangement. The heater, a spiral of thoriated W wire, is located concentrically within the Pd thimble. An outer Heliarc weld ring brazed to the inlet tubulation forms the outlet assembly. The heater requires a maximum of about 5.5 amp at gV and the Pd temperature is about 270’C at 2oW with I atm inlet and 5-10 mm Hg outlet pressures.

L. A. NOBLE, W. H. SAIN and R. K. WAITS, Rev, SCi.

Infrared Absorption Spectra of Alkali Metal Nitrates and Nitrites Above and Below the Melting Point J. GREENBERG and L. J. HALLGREN, J . Chem. Phys.,

Spectra of fused LiNO,, NaNO,, KNO,, RbNO,, CsNO,, NaNO, and KNO, were obtained by supporting the salts in the interstices of a 32 mesh Pt screen. Spectra below the melting points were obtained by allowing the salt to solidify on the screen. The screen was heated by the passage of an electric current and temperatures were measured by a Pt : IO:, Rh-Pt thermocouple.

Platinum-to-Pyrex Tubular Housekeeper Seals B. B. GRAVES, Rev. sci. Instr., 1960, 31, (3), 349- 350 A modification of the Housekeeper technique for sealing Pt to Pyrex entails reduction of the included angle of the feather edge of the Pt from 9” to between I’ and 14”. Methods of producing the edges and of testing the seals are described.

1960, 331 (3), 900-902

CATALYSIS Hydrogenation of Unsaturated Compounds in the Presence of Colloidal Palladium. XI. Hydrogenation of Vinylacetylene KH. v. BAL’YAN and N. A. BOROVIKOVA, J. Gen. Chem.U.S.S.R., 1959,29, (8),2516-2519 (Transl. of Zhur. ObshcheiKhim., 1959,29, (8), 2553-2556) The hydrogenation was carried out with ratios of vinylacetylene to hydrogen of I : I, I : 0.75, and I : 0.5 (in moles) and the effect of various additives on the composition of the hydrogenation products was studied. It was found that without additives and at any ratio of thc reactants, buty-


lenes and butane were formed together with a predominant amount of butadiene. Butylene formation falls with a decrease in the amount of hydrogen used. Pb(C,H,O,), and Cu(C2H302), Slow the hydrogenation reaction, decrease the butylene content, and increase thc yield of butadiene.

XII. Hydrogenation of Alkylacetylenes and Phenylacetylene KH. v. BAL’YAN and N. A. BOROVIKOVA, J . Gen. Ckem. U.S.S.R., 1959, 29, (81, 2520-2523 (Transl. of Zhzrr. Obshchei Khim., 1959, 29, (8),

Some monoalkylacetylenes and phenylacetylene were hydrogenated with colloidal Pd in a CH,COOH solution. It was found that hydrogenation proceeds selectively at the triple bond to form the corresponding olefins and styrene. After the addition of the first two atoms of hydrogen, the hydrogenation rate increases sharply and then decreases again.

Hydrogenation and Dehydrogenation J. T. BRADBURY, W. M. KEELY, F. J. O’HARA and R. F. VANCE, Ind. Eng. Chem., 1960, 52, (9), 803-806 In this review of recent literature on hydrogenation and dehydrogenation processes, the many uses of Pt metal and other catalysts are outlined. Fundamental studies as well as many industrial processes are reviewed. ( I I I references.)

2557-2559)

Purifying Hydrogen by Selective Oxidation of Carbon Monoxide M. L. morn, A. w. GREEN, G. corn and H. c. ANDERSEN, Ind. Eng. Chem., 1960, gz, (IO),

Laboratory and pilot plant work in which CO in NH, synthesis gas was oxidised catalytically to CO, with air or oxygen is described. The selective oxidation process was studied in relation to hydrogen and CO content of the gas stream, oxygen/CO ratio, catalyst composition, space velocity and temperature. Effective catalysts for the reaction in the temperature range 250-320°F are supported Pt, Rh, Rh-Pt and Ru. The temperature is held within the selective range by steam dilution. In C0,-free gas streams, ao4,CO may be reduced to 10 p.p.m. Proposed single- and two-stage oxidation units are illustrated.

841-844

A New Catalyst System for the Polymerisa- tion of Acetylenic Compounds L. B. LUTTNGER, Chem. & Ind., 1960, (36), 1135 The system consists of a freshly prepared mixture of an hydridic reducing agent (e.g. an alkali borohydride, LiAlH, or B,H,) with a salt or complex of a Group VIII metal (e.g. Co, Ni, Ru, Os, Pt or Pd). This system is effective under wide variations in composition and conditions.

Derivation of an Equation for the Kinetics of Hydrogenation of Benzene by Hydrogen in the Presence of Palladium Catalysts I. M. KOLESNIKOV, Zhur. Fiz. I<&n., 1960, 34, (7), 1528-1533 (English summary) The derived equation was applied to experimental results previously obtained using catalysts containing 1.4, 1.03, 0.49 and 0.18% Pd. It was shown that the adsorption of CbHs on the catalyst is considerablc. “Fatiguability” of the catalyst varies inverscly with the Pd content. The concept of the uniformity of the catalytic surface of Pd is shown to be applicable to this reaction.

Progress in the Study of Heterogeneous Catalysis

264-274 The course of catalytic reactions has been followed by using the mass spectrometer to analyse reaction products. Types of reactions studied were (i) exchange reactions with deu- terium, (ii) reactions involving deuteration, and (iii) reactions with hydrogen. Metal catalysts used in the various reactions included films of Ni, Mo, W, Pd, Pt, and Rh and some supported and wire types. In order to explain the experimental results it was necessary to consider the types of adsorbed species present on the catalysts and the manner in which the relative stabilities or reactivities of the species affect the mechanism of heterogeneous catalysis. Examples of each type of reaction arc discussed. (28 references.)

C . KEMBALL, PrOC. Chem. SOL., 1960, (Aug.),

Hydrogenation of Methyl Oleate in Solvents E. n. COUSINS and R. O. FEUGE, J. Amer. Oil Chem.

Hydrogenation was carried out to an iodine value of about 50 at 30°C and under atmospheric pressure with the methyl oleate alone or dissolved in C,H,OH, C‘H,,, CH,COOH or n-butyl ethyl ether. Of the total double bonds produced with a 100,; PdjC catalyst, with or without a solvent, 76.6-79.1:/, were trans bonds. With Raney Ni and solvents, trans bonds obtained were in the range 20.7-34.8%. When Raney Ni without a solvent and the Pd catalyst were used, positional isomers were formed extensively. Raney Ni with solvcnts gave products with a large proportion of double bonds in the 9-position.

Hydrogenation of Fatty Oils with Palladium Catalysts. V. Products of the Tall Oil Industry M. ZAJCEW, J . Amer. Oil Chem. SOC., 1960, 37, (IO), 473-475 Tall oil distillate was reduced to an iodine number of 22 using a 5”; Pd/C catalyst with a pressure of 2600 psi at 200’C. The resulting tall oil fatty acids were reduced using a Pd/C catalyst and the linoleic acid, cis-oleic acid,

SOC., 1960, 37, (91, 435-438


saturated acid and trans-isomers produced were determined. Pt, Ir, Rh and Ru were also examined for activity, selectivity and tendency to form trans-isomers and were found to be less suitable catalysts.

Development of Gas-Recombination Cata- lysts. Palladium Catalyst Development J. P. MCBRIDE and L. E. MORSE, U.S.A.E.C. Homogeneous Reactor Programme Quarterly Pro- gress Report, Apr. 30, 1960, ORNL-2947, 87-90 The sol method of preparing the Pd/ThO, catalyst is described. The effects of catalyst concentration and pretreatment with oxygen or hydrogen and of T h o , slurry concentration on catalytic activity in the hydrogen-oxygen reaction were studied. Specific activity of the sol- prepared catalyst appears to be independent of the type and concentration of the slurry solids. Pretreatment of the slurry catalyst system with hydrogen or maintaining an excess hydrogen overpressure results in a greatly increased specific activity.

Kinetics of the Reaction between Hydrogen and Oxygen on Platinum E. N. KIIAR'KOVSKAYA, G. K. BORESKOV and M. G. SLIN'KO, Proc. Acad. Sci. U.S.S.R., Phys. Chem. Section, 1959, 127, (I-6), 563-566 (Transl. of Doklady Akad. Nauk S.S.S.R., 1959, 127, (I),

A stationary flow method was used to mcasure the catalytic activity of a Pt wire working in the temperature range 20 to 180°C and at pressures from 50 to 750 mm with various initial reaction mixtures. The gases were circulated at 4m-1100 l/hr. It was found that with a large excess of hydrogen in the gas mixture the reaction was first order with respect to oxygen. With a large excess of oxygen and with high Pt activity the reaction is first order with respect to hydrogen, but with low Pt activity the order with respect to hydrogen is reduced to 0.1-0.2. The relationship between reaction rate and the concentration of oxygen and hydrogen was studied. Results are discussed in terms of the various forms of chernisorption which occur.

145-148)

Hydrogenation of Furan Compounds on Platinum and Rhodium Catalysts N. I. SHUIKIN and I. F. BEL'SKII, J . Gen. Chem. U.S.S.R., 1959, 29, (4), 1063-1065 (Transl. of Zhur. Obschchei Khim., 1959, 29, (4), 1093-1095) The furans were hydrogenated on Pt /C and RhjC in the vapour phase at various temperatures. I t was found that with a-alkenyl furans at 150"C, reduction of the olefin bond in the side chain gives the corresponding a-alkyl furans in 90-95?,, yield, On PtjC at 150°C the furan ring reacts slowly with hydrogen, undergoing hydrogenolysis at the double bonds (z0-25?/,) and hydrogenolysis at the 1-5 C-0 bond (75-So"&). At zm"C

on Rh/C, the furan ring undergoes hydrogenation into tetrahydrofuran (40 y o ) and hydrogenolysis at the 1-5 C - 0 bond with the formation of the corresponding ketone (607,). On Rh/C at 300°C there is only hydrogenolysis of the furan ring.

Reaction of Polyhalornethanes with Enol- ethers of A4-3-Ketosteroids. A Kew Path- way to 6a-Methylsteroids s. LIISBERG, w. 0. GODTFREDSEN and s . VANGEDAL,

Tetrahedron, 1960, 9, (3/4), 149-155 Reaction of enol ethers of A4-3-ketosteroids with CBr, affords via 6-tribromomethylsteroids the corresponding 6-dibromomethylene-A4-3-ketosteroids. Upon catalytic hydrogenolysis over Pd/SrCO, these are smoothly transformed into 6-methyl-AL-3-ketosteroids. Other polyhalornethanes react in a similar way with enol ethers of A l-3-ketosteroids.

The Heterogeneous Catalysis by Metals of Electron-Transfer Reactions in Solution M. SPIRO, 3. Chem. SOC., 1960 (Sep.), 3678-3679 The catalytic action of Pt, Ru, Ir, Pd, and Au in the reaction z F ~ ( C N ) , ~ - + ~ I - + Z F ~ ( C N ) ~ ~ - + I,- was observed. Pt and Hg were also exposed to the reactions 2Fe3' t3I-+zFe2+--j I,- and S,O,Z-+ 31-+2s0,2-~I,-. Results may be explained on the hypothesis that iodide ions and oxidant ions are adsorbed on the metal surface and that electrons may be transferred between them through the metal.

The Mechanism of the Reactions between Palladium Salts and Olefins in Hydroxyl- Bearing Solvents I. I. MOISEYEV, M. N. VARGAFTIK and YA. K. SYRKIN, Doklady Akad. Nauk S.S.S.R., 1960, 133, (2), 377-380 Four types of reaction studied were: (i) interaction between the (PdCl,.C,H,), complex and non-aqueous solvents; (ii) interaction between PdC1, and C,H, in glacial CH,COOH containing CH,COONa; (iii) oxidation of C,H, by n- benzoquinone in glacial CH,COOH in the presence of PdC1,; (iv) oxidation of C,H, by n-benzoquinone in alcohol solution in the presence of PdCls. It is suggested that the decomposition of the x-complex in hydroxyl-bearing solvents entails intermediate formation of vinyl compounds. Methods of preparation of complex vinyl esters and of acetals are indicated.

Evolution of Atomic Oxygen from Platinum Surface Treated Previously with Nitrous Oxide K. MITANI and Y. HARANG, null. Chem. Soc.Japan,

Atomic oxygen was evolved in vacuo on heating to 1400'C a Pt surface previously treated at

1960, 33, (8), 1147


I 100°C with N,O at pressures of 10-50 mm Hg. A dark brown film of PtO, deposited on the wall of the reaction vessel. It is believed that PtO, formed on the Pt surface is the source of the atomic oxygen.

The Treatment of Nitric Acid Plant Tail Gas W. FLETCHER, Brit. Chem. Eng., 1960, 5, (II), 789-790 The tail gas, which usually contains 0.3-0.50/, NO,, 2-474 excess oxygen and nitrogen, may be catalytically reduced by hydrogen, CH, or other fuel gases. Four types of catalyst at present in use are: (i) Pt metals deposited on A1,0, spheres or pellets; (ii) Pt metals on ceramic pellets; (iii) supported Ni-Cu; (iv) Pt metals deposited on crimped Ni-Cr ribbon. The designs of the reactors is discussed and operating conditions are described in detail.

Thermal and Catalytic Decomposition of Hydrocarbons A. J. DE ROSSET and c. v. BERGER, Ind. Eng. Chem., 1960, 52, (81, 711-716 Recent literature concerning the processes of thermal decomposition, catalytic cracking, catalytic reforming and dehydrogenation in petroleum refining is reviewed. Both industrial methods and research work are outlined. (100 references.)

Heterogeneous Catalysis in the Petroleum Jildllstry H. PICHLER, Trans. Instn. Chem. Engrs., 1960, 38, (41, 225-233 The history of the development of the processes of hydrogenation, oxidation, cracking, dehydrogenation, isomerisation, reforming and polymer- isation is given briefly in this review. Funda- mental properties of catalytic reactions are discussed. Reaction mechanisms and properties of the Pt metal and base metal catalysts for CO- hydrogenation, catalytic cracking, reforming and Ziegler reactions are examined. (20 references.)

Kinetics of n-Pentane Isomerisation over Pt/Al,O, Catalyst

J . Phys. Chem., 1960,64, (7), 892-894 The investigation was carried out at 372°C in a flow reactor in the presence of added hydrogen. Pressures varied from 7.7 to 27.7 atm and the hydrogenln-pentane ratio varied from 1.4 to 18. The isomerisation rate was found to be independent of the total pressure at a fixed n-pcntane: hydrogen mole ratio and to be correlated with the n-pentane/hydrogen mole ratio. A mechanism by which isomerisation proceeds via an olefin intermediate, n-pentene, which migrates to acidic sites to isomerise, is supported by these results. The isomerisation of the intermediate olefin is the rate-controlling step.

J. H. SINFELT, H. HURWITZ and J. C. ROHRER,

The Correlation between the Activity of a Platforming Catalyst and Certain Physical Properties

and I. BALLY, J . Chim. Phys., 1960, 57, (51, 409-415 An active and thermally deactivated I', I"/ A1,0, catalyst was studied by X-ray and electrical methods. It was found that the active support material is q-Al,O, and not ;.-A1,0,. The decrease in catalyst activity results from a decrease in the degree of dispersion of the Pt as well as from deformation of the crystal lattice of the Pt. In the temperature range 429°-5000c, the specific electrical conductivity of the active catalyst in air and in hydrogen is greater than that of the deactivated catalyst. The energy of activation of the electrical conductivity increases on deactivation of the catalyst. The existence of a correlation between physical properties of the catalyst and its activity in the Platforming process are indicated.

I . V. NICOLESCU, A. POPESCU, C. FOREDA, A. PAPIA

An Investigation of Thiophene Poisoning Effect on a Platinum Catalyst under Re- forming Conditions. 3. Effeet of Tempera- ture and Hydrogen Pressure KH. M. MINACHEV, D. A. KONDRAT'EV and 0. K. SHCHUKINA, Izvest. Akad. Nauk S.S.S.R., Otdel. Khim. Nauk, 1960, (7), 1263-1266 The deactivation of a 19; Pt/AI,O, catalyst in the dehydrogenation of C,H,, containing 2.65% thiophene was studied at a constant hydrogen pressure of 20 atm with pressures of 10-40 atm and temperatures of 450" and 475°C. It was found that the degree of hydrogenation increases with increase of tcmperature and diminishes with increasing pressures. The specific surface area of the deactivated catalysts diminishes with increased temperature, but in practice is not changed with alteration of pressure.

A Study of the Effect of the Specific Surface Area of Platinised Alumina-Silica on the Degree of n-Nonane Conversion. 2. Change in the Catalytic Activity of Platinised Alumina-Silica in the Course of the Carrier Treatment by Water Vapour KH. M. MINACHEV, N. I. SHUIKIN and M. A. MARKOV, Izvest. Akad. Nauk S.S.S.R., Otdel, Khim. Nauk, 1960, (8), 1466-1470 The investigation was carried out using 0 . 5 ~ ~ Pt iAl,O,\SiO, catalysts with varying specific surface area at temperatures of 360-450°C and a hydrogen pressure of 10 atm in a fluid system. It was found that the degree of hydrocracking is reduced with decreasing specific surface area of the catalyst. A yield of 5400 i-C,H,, was obtained at 380'C and at 450°C with catalysts having specific surface areas of 320 mz'g and 60 m2 ;g, respectively.


ELECTRICAL ENGINEERING An Investigation of the Effect of Materials Used for the Construction of Telephone Exchanges on Contact Materials Containing Silver and Palladium H. LIPKE and W. CLEMENT, Xachrichtentech. Z.

Contact materials investigated at constant temperature and humidity levels were Ag, Pd, 50y0 Pd-Ag and 30:~ Pd-Ag. Resistance changes with time were the basis for conclusions on the effects of the various materials on the contacts. Organic substances such as oil of turpentine and linseed oil mainly affect Pd-containing contacts.

(hr*T.Z.), 1960, 133 (9) , 431-435

CHEMICAL TECHNOLOGY The Use of Precious Metals in Plant Con- struction M. WITTUM, Metall, 1960, 14, (9), 897-901 Uses of Ag, Au, Pt and their alloys in the construction of chemical plant are described. The suitability of these metals for this purpose is shown by a study of their corrosion resistance and mechanical and physical properties.

GLASS TECHNOLOGY The Increasing Use of Platinum in the Glass Industry KASWANT, Sprechsaal, 1960, 93, (IS), 473-477 Economic aspects of the world supply and con- sumption of the Pt metals are reviewed. The principal physical properties of these metals are given in graphical and tabular form. Examples given of the applications of Rh-Pt alloys include feeders, crucibles for melting optical glass and bushings for glass fibre manufacture. Mention is made of the use of a Re-Pt alloy for silicate melts.

TEMPERATURE MEASUREMENT Techniques in Calorimetry. I. A Noble- Metal Thermocouple for Differential Use E. D. WEST, Rev. Sci. Instr., 1960, 31, (S), 896-897 A 40"" Pd-Au: 1o0/, Rh-Pt thermocouple for use in an adiabatic calorimeter up to 600°C is described. The e.m.f. of the thermocouple together with dEjdT values are shown on a graph.

NEW PATENTS Thermocouples electrical make-and-break members have, at the ELECTROFLO METERS GO. LTD. et al. British Patent point of contact, a flame-sprayed coating of 845,031 platinum or of an alloy of platinum with another A thermocouple consists of an insulating sheath formed as a solid elongated block of high-refrac-

Of the Same group. - L

tory ceramic, the hot junction being embedded in the block close to one end and the thermocouple wires emerging from the other end. A metal cladding is provided around the block leaving the hot junction end exposed. The thermocouple wires are of platinum-rhodium 20% alloy and platinum-rhodium 4096 alloy.

Purification of Ethylene ENGELHARD INDUSTRIES INC. British Patent 846,077 Carbon monoxide is removed from a mixture thereof with ethylene and oxygen by passing the mixture over a rhodium-containing catalyst at 25-15oOC. The catalyst is preferably rhodium on activated alumina. Another platinum group metal, e.g. platinum, may also be included.

Electrical Contacts NORTON GRINDING WHEEL co. LTD. British Patent

For the purpose of inhibiting the detrimental effects of disruption at the points of contact,

847,200

Platinum Metals Rev., 1961, 5, (l), 3 8 4 0

Hydroforming Process THE BRITISH PETROLEUM GO. LTD. British Patent 847,728 The first stage of a two-stage platinum reforming process for treating petroleum hydrocarbons boiling within the gasoline and naphtha ranges is carried out at at least 450°C with a catalyst of platinum on a normally acidic support rendered non-acidic by the addition of sodium; the second stage is carried out at a similar temperature using a catalyst of platinum on an acidic support. Support preferably consists of alumina.

Dehydrogenation of Alicyclic Alcohols

849,135 An alicyclic alcohol is dehydrogenated to an alicyclic ketone by passing the alcohol at a pressure from subatmospheric to atmospheric over a catalyst consisting of ruthenium supported on carbon preferably at a temperature of 50- 700°C.

ENGELHARD INDUSTRIES INC. British Patent

38

Nitrocy clododecanes

Patent 849,237 A palladium-barium sulphate catalyst is used in a process for making the oxime of cyclodode- canone by mild selective reduction of aci-nitro- cyclododecane.

Electrical Resistance Element BECKMAN INSTRUMENTS INC. British Patent 849,305 A resistance element consists of a high temperature resistant base on which is fired a layer of resistance material composed of a minor amount of one or more noble metals and a major amount of non-absorptive, electrically non-conductive binder material of glass of lower melting point than the metal, the metal being finely divided and dispersed throughout a continuous phase of solidified glass. The metal, which may be platinum, rhodium or palladium, constitutes 1-16% by weight of the resistance material.

Chlorination of Hydrocarbons BADISCHE ANILIN & SODA PABRIK A.G. British Patent 849,434 Chlorination of a hydrocarbon or a partly hydrogenated derivative thereof is effected by allowing chlorine to act on it in the gas phase at a temperature at or above its boiling point up to about 400°C in the presence of a catalyst containing a halide of platinum, palladium, iridium or rhodium.

Magnet Alloys JOHNSON, MATTHEY & co., LTD. British Patent 849,505 A cobalt-platinum alloy (17-27% cobalt) is heat- treated to produce permanent magnet properties at a temperature to produce disordering within the alloy, followed by quenching to an ordering temperature of 5oo-750°C, the alloy being main- tained at this temperature for i-5 hours and finally quenched in water or allowed to cool in air.

Electric Furnace Heater Elements JOHNSON, MATTHEY & CO., LTD. British Patent 849,507 An electric furnace heater element is made by flame-spraying on to a platinum group metal or alloy wire or strip a thin layer of alumina of 2-50 thousandths of an inch. A platinum-rhodium (10-40%) alloy is used.

Spinning Nozzles W. C. HERAEUS G.m.b.H. British Patent 849,840 A spinning nozzle is made of an alloy of palladium and I-30% ruthenium, up to 15y0 of the palladium being replaceable by another platinum group metal. Ex: (I) 90% Pd, 10% Ru; (2) 90% Pd, 5 % Ru and 5 % Ir; (3) 85% Pd, 5 % Ru and 10% Ir; (4) 85% Pd, 10% Ru and 5 % Rh. Heat-treatment is stated to increase the hardness.

STUDIENGESELLSCHAFT KOHLE m.b.H. British Purification of Waste Gases

849,842 Waste gases containing oxides of nitrogen are purified by contacting the gases, mixed with a gaseous hydrocarbon fuel, with a rhodium- or palladium-containing catalyst at at least 690°F. The catalyst may consist of palladium, palladium and rhodium, or palladium and/or rhodium mixed with another platinum group metal. An alumina support is used.

Photographic Screens GRATICIJLES LTD. British Patent 850,047 A graticule or half-tone or gravure screen is made by forming a photographic image thereof of a platinum group metal in a collodion emulsion on a glass support, treating it with an aqueous solution of a soluble salt of tin, bismuth or lead and burning off the collodion.

Hydrogen Gauges WESTINGHOUSE ELECTRIC COW. British Patent

A hydrogen gauge includes a first conductor, the electrical resistance of which changes in response to changes in environmental hydrogen concentration, a second conductor exposed to the same environment, the resistance of which is not affected thereby, but having the same temperature coefficient of resistance as the first conductor, both conductors being insulated from one another and means for measuring the electrical resistance of each conductor or the differential resistance between them. The first conductor is formed of palladium and the second of platinum.

Electrical Contacts METALS AND CONTROLS cow. British Patent 850,185 One contact of a co-operating contact pair is composed of an alloy of 60-80Y0 by wt. of palladium, 0.5-1.8% of nickel, cobalt or copper or mixtures thereof and remainder silver. The other contact consists of an alloy of 50-80% by wt. of gold and balance silver. The combination is stated to have an average life of three times those at present used in voltage regulators.

Purification of Gas Mixtures IMPERIAL CHEMICAL INDUSTRIES LTD. British Patent 850,760 The amount of methyl-acetylene in propylene- rich gas is decreased by passing the gas, together with hydrogen, over a catalyst comprising 0.01% to 0.1% of palladium on gamma alumina. The catalyst is made by precipitating aluminium hydroxide from aluminium nitrate by addition of aqueous ammonia, separating, drying, calcining and pelleting to give pellets of gamma alumina and then impregnating them with an aqueous

ENGELHARD INDUSTRIES INC. British Patent

850,064


solution of an appropriate palladium salt, followed by heating in hydrogen. See also No. 850,761 covering the production of propylene free from methyl acetylene.

Alloy for Spinning Nozzles

German Patent 1,075,838 A spinning nozzle is formed of an alloy composed of more than 32%, up to 93%, platinum, 0.05-294, preferably 0.25-1 96, rhenium and remainder gold.

Palladium Alloy for Spinning Nozzles

The palladium- and iridium-containing alloy for making spinning nozzles for the production of artificial fibres, according to German patent No. 1,010,742, is modified so as to contain from 7:/; to less than 15% iridium, j-30:/~, preferably 10-2 j %, rhodium and remainder palladium.

Alloy for Electrical Contacts W. C. HERAEUS G.m.b.H. German Patent 1,077,435 A rhodium-nickel alloy containing 10-25 :L, preferably 12-21 24, nickel, remainder rhodium, is used for making electrical contacts, particularly telephone selector contacts,

Hydrocracking Catalyst PHILLIPS PETROLEUM CO. U.S. Patent 2,946,739 Wafra 400°F plus crude is hydrocracked at 750-85ooF, a pressure of 500-3000 psig and a liquid hourly space velocity of 0.1-1, using 500-5000 cu. ft of hydrogen per barrel of oil with a catalyst containing 0.1-1 wt.Yn of rhodium, 1-5 wt.:a of cobalt, 3-10 wt.u& of molybdenum, on an alumina support.

Selective Hydrogenation and Catalyst therefor CHEMETRON CORP. U.S. Patent 2,946,829 A catalyst for the seleaive hydrogenation of highly unsaturated hydrocarbons in a concentrated olefin stream is composed of o.or-o.09 wt.% of palladium metal on an alumina support, the catalyst having a pore volume of surface pores of a threshold diameter not over 8008, in the range of 0.6-0.4 cc/g and the palladium being mainly concentrated in the external portions of the carrier.

CatdlySt STANDARD OIL 60. U.S. Patent 2,948,672 A hydrocarbon conversion process is carried out using a platinum-alumina hydroforming catalyst of improved activity containing 0.05-1 04 by wt. of platinum, based on dry A1,0,, uniformly dis- tributed in it. The catalyst is prepared by impregnating solid hydrous alumina containing 1-300; by wt. of combined water, dry basis, with a solution of a platinum compound in

DEUTSCHE GOLD-UND-SILBER-SCHEIDEANSTALT

W. C. HERAEUS G.m.b.H. German Patent 1,077,434


amount to give the required amount of platinum, drying and calcining. Impregnation is effected in the presence of an aqueous solution of 'J.

halogen-containing aliphatic carboxylic acid having 2-5 carbon atoms in the molecule and an ionisation constant greater than I O - ~ at 25°C in a molar ratio to alumina of o.mr-o.05.

Catalysts STANDARD OIL co. U.S. Patent 2,950,243 A hydroforming process is carried out with a platinum-alumina catalyst prepared by forming a m:ixture by commingling an alumina hydrosol with a solution consisting of water, ammonium hydroxide, or a water-soluble amine or a quater- nary ammonium hydroxide, and a water-miscible oxygen-containing organic solvent (an alkyY alcohol, acetone, an alkyl glycol or an alkyl ether). Sufficient alkaline substance is used to adjuirt the pH of the mixture to 8.5-12; the solvmt comprising 10-50Y; by vol. of thc mixture. The mixture is held at 50-250"F for over I hour, whereby the alumina present is converted to a filterable slurry of solid hydrous alumina from which the alumina is separated and dried to a volatile content of 15-500& wet basis. The dried alumina is then impregnated with an aqueous chloroplatinic acid solution to a platinum level of o.o5-10& by wt., based on dry A1,0,, dried and calcined.

Platinum Catalyst ESSO RESEARCH & ENGINEERING GO. US. Patent

In the manufacture of an alumina supported platinum catalyst activated by heat-treatmentJ the impregnated alumina is heatcd at at least 900°F for a suitable time to form platinum metal crystallite particles from the impregnating solution, the heat-treatment being controlled to keep the particles from growing to a crystallite size of ovI:r SOB, as shown by an X-ray test.

Conversion of Petroleum UNION CARBIDE CORP. U.S. Patent 2,953,509 The viscosity and boiling range of petroleum are reduced by gamma irradiating the petroleum with about IOO million rantgens from a cobalt 60 bomb in the presence of a catalyst of platinum oxide or palladium chloride.

2,95'W59

Preparing Beta-Phenyl-Ethylchlorosilanes UNION CARBIDE CORP. U.S. Patent 2,954,390 Beta-phenyl-ethylchlorosilanes are produced by forming a mixture of styrene, a chlorosilane containing at least one hydrogen atom bonded to silicon, tetrahydrofuran in amount from 0.5 to 10 times the weight of styrene, and a catalyst consisting of chloroplatinic acid, platinum or platinum on an inert carbon-free carrier, and heating the mixture to cause addition of the chlorosilane to the styrene.

Documents

PLATINUM REVIEW · in other directions. The production of staple fibre began in 1930, and by 1940 production was greater than that of continuous filament yarn. Diversification here