ANL-6684 Chemis t ry ( T I D - 4 5 0 0 , 22nd Ed.) AEC Research and Development Report

ARGONNE NATIONAL LABORATORY 9700 South Cass Avenue Argonne, Illinois 60440

THE MECHANISM AND KINETICS OF THE REACTION BETWEEN NICKEL AND FLUORINE

by

R. L, J a r r y , W. H. Gunther, and J . F i sche r

Chemical Engineering Division

August 1963

Operated by The Universi ty of Chicago under

Contract W-31 - I09-eng-38 with the

U. S. Atomic Energy Commiss ion

DISCLAIMER

This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency Thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

DISCLAIMER Portions of this document may be illegible in electronic image products. Images are produced from the best available original document.

TABLE OF CONTENTS

Page

ABSTRACT 5

I. INTRODUCTION 6

II. MECHANISM OF THE NICKEL-FLUORINE REACTION 9

A. Mate r ia l s , Apparatus , and Exper imenta l P rocedure 9

B. Resul ts and Discussion 11

III. THE KINETICS OF THE REACTION OF NICKEL WITH FLUORINE. , 15

A. Mate r ia l s , Apparatus , and Exper imenta l P rocedure . . . . . 15

B. Resul ts and Discussion 17

IV. SUMMARY . 25

V. ACKNOWLEDGMENTS 26

VI. BIBLIOGRAPHY 27

# LIST OF FIGURES

No. Tit le Page

1. Migration P r o c e s s e s in Gas-Meta l Reactions 6 2. Calculated Concentration of Radioactivity in Oxide Layer

Based on the Cationic Vacancy Mechanism 7 3. Nickel-63 Plat ing Cell 10 4. Wedge Specimen for Impinging Scale Experiment . 10 5. Micrograph of Impinging Nickel Fluor ide Scales 12 6. Micrograph of Impinging Nickel Oxide Scales . . . . . . . . . . . . 12 7. Micrograph of Autoradiographic Emulsion Showing

Nickel-63 Activity in Nickel Fluor ide Scale 13 8. Micrograph of Autoradiographic Emulsion Showing

Nickel-63 Activity in Nickel Oxide Scale 13

9. Apparatus for the Study of the Kinetics of the Nickel-Fluor ine Reaction 15

10. Reaction Vesse l and Nickel Block. 16

11. Linear Plot of Rate of Reaction of Nickel with Fluorine in the Tempera tu re Range from 300 to 600 C . 18

12. Logari thmic Plot of Rate of Reaction of Nickel with Fluor ine in the Tempera tu re Range from 300 to 600 C . . . . . . 18

13. Ar rhen ius Plot of Parabol ic Rate Constants for the Reaction Ni + F j -> NiF2 in the Tempera tu re Range from 300 to 600 C . . 19

14. Comparison of the Reaction between Fluorine and Nivac and A-Nickel in the Tempera tu re Range from 400 to 600 C 20

15. The Fluorinat ion of A-Nickel in the Tempera tu re Range from 400 to 600 C . . . . . . . . . . . . . . . . . . . . . . . . 21

16. P r e s s u r e Dependence of the Nickel -Fluor ine React ion. . . . . . 24 17. Rate of Change of Scale Thickness as a Function of Fluorine

P r e s s u r e 24

LIST OF TABLES

No. Title Page

1. Parabol ic Rate Constants for the Nickel -Fluor ine Reaction Over the Tempera tu re Range from 3 00 to 600 C. . . . . . . . . 19

2. Nickel Fluoride Scale Thicknesses after 1000 Min of Reaction Timie for A-Nicke l . . 22

3. Parabol ic Rate Constants for the Nickel-Fluor ine Reaction at 500 C and Fluorine P r e s s u r e s of 100, 350 and 700 m m . . 22

4. The Effect of P r e s s u r e on the Rate of Buildup of A-Nickel Fluor ide Scale at 600 C 23

THE MECHANISM AND KINETICS OF THE REACTION BETWEEN NICKEL AND FLUORINE

by

R. L. J a r r y , W. H. Gunther, and J. F i scher

ABSTRACT

The mechanisxn and kinet ics of the nickel-fluorine react ion have been studied. Marke r (isotopic t r ace r ) exper iments , in which radioactive nickel-63 was used, and sca le- impingement exper iments , in which two scales formed during the react ion were forced to impinge upon each other, were c a r r i e d out to de termine whether nickel or fluorine mig ra t e s through the nickel fluoride scale formed during the fluorination of nickel. Similar exper iments were per formed with the nickel-oxygen system to verify the exper imenta l r e su l t s obtained in the nickel-f luorine study with those ob-tained in a reac t ion of known mechan i sm. The radioactive t r a c e r exper i -ments indicated that fluorine m i g r a t e s through the growing fluoride scale . This was shown by the lack of movement of the radioactive t r a c e r , which was found at the nickel fluoride scale-f luorine gas interface. In the nickel-oxygen exper imen t s , the radioact ivi ty was found to be distr ibuted through the oxide scale in a manner predic ted from the known mechanism. This resu l t was in accord with the accepted mechanism for that reaction, namely, that nickel m i g r a t e s through the nickel oxide scale to the nickel oxide-gas interface. In the fluoride sca le- impingement exper iments , the existence of an interface between the two sca les growing from opposing surfaces indicated that fluorine is the migrat ing species . In the oxide sca le - impingement exper iments , a continuous scale was formied, thereby indicating that nickel is the migra t ing species in this case .

The kinet ics of the nickel-f luorine react ion have been studied be -tween 300 and 600 C using high-puri ty and commerc i a l nickel. The p a r a -bolic ra te constants for the reac t ion with high-puri ty nickel were found to be 9.8, 81, 461, and I860 (/j g Fz/sq cm)^ per minute at 300, 400, 500, and 600 C, respec t ive ly .

No significant difference in react ion r a t e s for the two types of nickel was noted except in the init ial portion (less than 500 min) of the r e -action per iod. The parabol ic ra te was found to be independent of the p r e s -sure of fluorine over the range of 100 to 700 m m Hg when the thickness of the nickel fluoride scale was 10* A or l e s s . After a scale having a thick-ness of about 10 A had been deposited, the ra te of scale formation was found to vary with the one-half power of the fluorine p r e s s u r e .

I. INTRODUCTION

Fluorine is used in fluoride volatility processing of spent nuclear reactor fuels to convert uranium and plutonium to their respective hexa-fluorides. The best material of construction for use with fluorine at ele-vated temperatures, say 500 to 600 C, is nickel. Fluorine reacts with nickel to form a coherent, adherent scale of nickel fluoride which acts protectively by diminishing the rate of reaction. Several investigations of the corrosion of nickel have been reported,(1 "3) and a recent publica-tion summarizes the data available at the present time.(4) No description of the mechanism of the nickel-fluorine reaction has been reported.

Oxidation reactions of metals and alloys which result in protective scales, that is, a scale which controls the reaction rate in some manner proportional to its thickness, have been treated according to the theory developed by Wagner.(5) According to this theory, metal or nonmetai ions

are considered to be transported Figure 1

MIGRATION PROCESSES IN GAS METAL REACTIONS

across the growing scale to a reac-tion interface. Concurrently with the ion transport, vacancies, repre-senting vacant lattice sites, and electrons travel through the scale, thereby maintaining electrical neu-trality across the scale. This scheme is shown diagramimatically in Fig-ure 1. It follows from this consid-eration that in the case for which 3xietal-ion migration predominates the reaction occurs at the scale-gas interface. When nonmetal-ion mi-(A) Outward Migration of Positively Charged Metal Ions and Electrons, Reaction ,. -, . ^^.^^ ^ . i , ^ ^ ^ . , ^ + 4 . ^ ^ Occurs at d) g ration predominates, the reaction

(B) Inward Wigration of Negatively Charged Nonmetai Ions and Outward Migration O C C U r S a t t h e m e t a l - S C a l e i n t e r f a c e , of Electrons Reaction Occurs at (2) ^^^ classical example of the use of this mechanistic approach has been the study of the oxidation of copperw) in which it was shown that the copper ions migrated to the oxide-gas interface.

The Wagner Theory further states that reactions producing protec-tive scales follow a parabolic reaction rate law. The oxidation of nickel has also been shown to follow the parabolic rate law,(6) and measurements of the diffusion of nickel and oxygen in nickel oxide(7) have shown that the diffusion rate of nickel is greater by several orders of magnitude than that of oxygen.

7

Since react ion s i tes for the migrat ing meta l and nonmetai ions a r e different (the fo rmer r eac t s at the sca le -gas interface, the l a t t e r reac t s at the m e t a l - s c a l e interface), the determinat ion of the react ion site can serve as a means of elucidating the mechan ism of a react ion. Two different ap -proaches were used to indicate the location of the reaction site in this study of the nickel-f luorine react ion. To check the exper imental methods with a react ion of known mechan ism s imi la r experiments were performed with the nickel-oxygen sys tem. In the f i rs t experimental approach, a radioactive t r a c e r , n ickel -63, was used as a se l f -marker . Nickel-63 was plated on the specimens to be fluorinated or oxidized and the radioactivity in the reac ted specimiens was located by autoradiographic means .

It is possible to predic t the position of the activity in the result ing scale on the bas is of the work c a r r i e d out by Bardeen and associates.(S) In this work, the expected distr ibution of the radioactive se l f -marker was calculated according to the Wagner theory and verified experimental ly for the copper-oxygen sys tem. Additional verification of the expected dis t r ibu-tion of the activity was obtained by Castel lan and Moore.wj

The solid curve of Figure 2 shows the expected distribution when meta l - ion migra t ion predominates . In this case, there is a diminution of the radioactive t r a c e r from the oxide-gas interface to the me ta l - sca l e interface. For the case in which nonmetal- ion migrat ion through the scale predominates , the isotopic t r a c e r would not be involved and the activity would appear in a nar row band at the sca le -gas interface as shown by the dotted line in Figure 2. In the investigation of the oxidation of uranium by Schnizlein et aL,(!'-') the isotope uranium-235 was used as a se l f -marke r . The concentration of the alpha activity of the uranium-235 at the oxide-gas interface showed that migra t ion of the nonmetai, oxygen, predominated in this reaction.

Figure 2 CALCULATED CONCENTRATION OF

RADIOACTIVITY IN OXIDE LAYER BASED ON THE CATIONIC

VACANCY MECHANISM

0.25 0.50 0.75

RELATIVE DISTANCE FROM METAL

The second technique used an exper iment in which the cha rac te r of the interface, at the point at which two sca les of the same m a t e r i a l , nickel fluoride or nickel oxide, growing toward each other from near ly para l le l nickel surfaces would meet , as an indication of the mechan i sm. (This tech-nique wil l be r e f e r r e d to hereaf ter as the "impinging sca le" technique.) If metal a toms were the pr incipal species migra t ing through the scale to reac t at the sca le -gas interface, the two scale surfaces growing toward one another would fuse into one scale as the meta l ions from one scale surface migra ted into the other . If the mechanismi were dependent on the movement of the nonmetai a c r o s s the forming sca les , the two sca les would not fuse upon coming together , and an interface would be p resen t . This technique was used by Schnizlein(lO) to identify the diffusing species in the oxidation of uranium.

The kinet ics of the nickel-f luorine react ion were studied over the t empera tu re range from 300 to 600 C by a manomet r i c technique.

IL MECHANISM OF THE NICKEL-FLUORINE REACTION

A. Mate r i a l s , Appara tus , and Exper imenta l P rocedure

The fluorine used in this work was procured from the General Chemical Company. The puri ty of the fluorine was assayed to be 98.2 v /o by the m e r c u r y react ion me thod . ( l l ) Hydrogen fluoride was removed from the fluorine by passing the gas through a sodium fluoride t rap kept at about 100 C.

The nickel used was commerc i a l A-nickel which had a puri ty of 99.4 percent . Analyses by chemical and spectrographic means showed that the pr incipal impur i t i e s , expres sed in pa r t s per mil l ion, were as follows: manganese , 2800; carbon, 700; iron, 1000; silicon, 800; and copper, 500.

The nickel-63 t r a c e r was obtained from Oak Ridge National Labo-r a to ry in 5-mc lots as an acid chloride solution. Nickel-63 is a pure beta emi t t e r with an energy of 63 kev. A smal l amount of nickel-59, with a K-capture X ray of 1.07 Mev, was p re sen t as a contaminant to the extent of about 0.01 percen t . This gamma activity was not objectionable as it did not interfere with the autoradiographic p roces s .

Two types of str ipping film were used in this work: Kodak Expe r i -menta l Pe rmeab le Base Stripping F i lm, which consisted of b-jl emulsion overload with 5 jU of gelatin on a ro l l - f i lm backing., and Kodak Autoradio-graphic Filxn AR-10, which consis ted of a 5-/ i - thick emulsion overlaid with 10 /i of gelatin on a g lass -p la te backing. Because of the g rea te r thickness of the AR-10 film, it was found to be eas i e r to handle for this type of use .

The fluorination and oxidation exper iments were ca r r i ed out in e lec t r ica l ly heated tube r e a c t o r s . The tube reac tor for the fluorinations was a 2-ft section of 2-in. nickel pipe with a welded plate at one end and a flange c losure at the other . A thermocouple tube made of - j- in. nickel tubing was welded through the top flange and extended to the midpoint of the r e a c -tion tube. Hooks welded to the thermocouple tube were used to support the sainple spec imens . A second--in. nickel tube, which was also welded through the top flange, and which extended to within one inch of the bottom of the react ion tube, se rved as an inlet for fluorine gas . The tube reac tor for the oxidation exper iments was a 10-in. section of 2 - in . -d iamete r nickel tubing with a welded cap at one end and a flange c losure at the other.

A nickel manifold connected to the reac tor sys tems provided access for vacuum, fluorine and oxygen sou rces , and p r e s s u r e - m e a s u r i n g devices. Both Bourdon-type gages and a Booth-Cromer null-point gage were used for p r e s s u r e m e a s u r e m e n t s .

Tempera tu re "was maintained by tube furnaces through a propor t ion-ally c ircui ted Variac controlled by a pyromete r cont ro l le r . The pyrometer

was activated by a ch romel -a lumel thermocouple in the thermocouple well of the reac tor . A s e c -ond chromel -a lumel thermocouple in the reac tor was used in conjunction with a Brown potentio-m e t e r for measur ing and recording the r e a c -tion t empera tu re .

Figure 3 NICKEL-63 PLATING

CELL

I 24/4C

(-) CATHODE

Nickel containing the nickel-63 t r a c e r was plated on the nickel coupons with the plating cell shown d iagrammat ica l ly in Figure 3. The cell was constructed of 30-mm Pyrex tubing, 80 mm in length, capped with a 24/40 standard taper joint. The platinum leads were sealed through the P y r e x for support without a t tempt-ing to produce gas- t ight sea l s .

The coupons to be plated with nickel-63 were one cm by five cm by 0.16 cm, and were polished with one-micron diamond paste and then degreased using acetone. The acid chloride solution containing the nickel-63 was made basic with ammonia to form the t e t raammine complex. A plating t ime of about 15 min at 1 0 ma and 2.2 v was requi red to obtain a 2 -/i-thick plate of nickel. Only the lower 1-2 cm of the coupon

was plated, the remainder of the coupon being masked with paraffin. The thickness of the plate was calculated from the weight gain of the coupon, the geometr ic a r ea , and the theoret ical c rys ta l density of nickel.

NICKEL COUPON soLUTiorv

LEVEL

Coupons used for the impinging scale exper iments were one cm by three cm by 0.16 era. A react ion specimen was p repa red by welding two coupons together along the one-cm edges so as to make an angle of about one degree between surfaces , as shown in Figure 4.

Figure 4

WEDGE SPECIMEN FOR IMPINGING SCALE EXPERIMENT

' \

018cm

The plated coupons and welded impinging scale specimens were reac ted with fluorine or oxygen in the following manner . The p repared coupons were placed in the r eac to r , and the sys tem was evacuated and tes ted for l eaks . Following this step, the reactant gas was admitted and the heating per iod was begun. This p rocedure was followed because it was found that s tar t ing the heating cycle after the fluorine was admitted to the r eac to r produced a m o r e adherent scale . Fluorinat ions were c a r r i e d out at 600 to 700 C for per iods of 24 to 36 hr . The oxidations were run at about 1000 C for per iods of 48 to 72 hr . After the react ion period, the r eac to r was evacuated and allowed to cool slowly for a period of about 12 to 24 hr before the samples were removed.

In o rde r to examine the specimens metal lographical ly or apply the autoradiographic emulsion, the coupons were mounted in Bakelite. The mounts were then sect ioned normal ly to the short axis of the coupon for the nickel-63 specimens and normal ly to the long axis for the impinging scale spec imens .

The autoradiographic technique descr ibed by Gombergl l^) was used in these exper iments . The specimen, mounted in Bakelite, was p repa red by polishing with 600 gr i t meta l lographic paper . The mount was then cleaned in an u l t rasonic bath to ensure the removal of res idual activity spread over the surface during the polishing.

The emulsion, which was about 5-/J. in th ickness , plus the 5- or 10-,a-thick gelatin l ayer , was removed from the filmi backing. The emul -sion, active side down, was floated onto the surface of the specimen using a drop of water containing a t r ace of wetting agent. An exposure time of five days was used, after which the emulsion was developed. After develop-ment the emuls ion was removed from the mount and mounted on a s tandard mic roscope sl ide. Removal of the developed einulsion from the specimen was found des i rab le because the background made it difficult to observe the details of the exposed emulsion. The activity and repl icat ion of the surface could easi ly be observed when the emulsion was mounted on the glass sl ide. F r o m the rep l ica ted surface it was possible to identify the interface regions without ambiguity,

B. Resul ts and Discussion

The resu l t s of the impinging scale exper iments a r e shown in F ig -u re s 5 and 6 which a r e mic rog raphs of samples which have been reac ted with fluorine and oxygen, respec t ive ly . It is apparent from Figure 5, that the impinging fluoride sca les a r e separa ted by an interface, which indicates that fluorine mig ra t ed from the gas - so l id interface through the fluoride scale to the nickel-nickel fluoride interface and that meta l migra t ion was negligible.

F i g u r e 5

M I C R O G R A P H O F IMPINGING N I C K E L F L U O R I D E S C A L E S

JOOu: A -

A and A\ nickel substrates; B and B', nickel fluoride scales; C, interface between nickel fluoride scales.

F i g u r e 6

MICROGRAPH O F IMPINGING N I C K E L OXIDE SCALES

*

lOOn . * > . %

^ -9 ^ ^ ^ \ '

\ :

A and A\ nickel substrates; B, continuous nickel oxide scale.

13

In F i g u r e 6, a c o n t i n u o u s o x i d e s c a l e i s s e e n b e t w e e n t h e t w o m e t a l s u r f a c e s . T h i s c o n f i r m s t h e f a c t t h a t t h e m e t a l m i g r a t e s t h r o u g h t h e m e t a l o x i d e s c a l e , a n d r e a c t s a t t h e m e t a l o x i d e - g a s i n t e r f a c e t o p r o d u c e a c o n -t i n u o u s o x i d e f i l m .

C o n s i d e r a b l e p o r o s i t y i n t h e n i c k e l o x i d e s c a l e i s e v i d e n t in t h e m i c r o g r a p h r e p r o d u c e d in F i g u r e 6. T h e a d j a c e n t m e t a l s u r f a c e s , w h i c h w e r e e t c h e d t o p r o v i d e m o r e c o n t r a s t w i t h t h e s c a l e , a l s o e x h i b i t p o r o s i t y . T h e p o r o s i t y of t h e o x i d e s c a l e c a n b e a t t r i b u t e d t o t h e r e m o v a l of c a t i o n v a c a n c i e s b y c o n d e n s a t i o n a n d p r e c i p i t a t i o n w i t h i n t h e o x i d e p h a s e . T h i s m e c h a n i s m f o r t h e r e m o v a l of c a t i o n v a c a n c i e s f r o m t h e m e t a l o x i d a t i o n s y s t e m w a s p r o p o s e d b y B i r c l i e n a l l . ( 1 3 ) T h e v a c a n c i e s a r e p r e s e n t in t h e s y s t e m a s a r e s u l t of c a t i o n d i f f u s i o n d u r i n g t h e r e a c t i o n . T h e p r e s e n c e of w h a t a p p e a r t o b e v o i d s in t h e m e t a l s u b s t r a t e m a y b e t h e r e s u l t of t h e p r o d u c t i o n of v a c a n c i e s a t t h e m e t a l - o x i d e i n t e r f a c e a n d t h e i r s u b s e q u e n t m i g r a t i o n t o t h e g r o w i n g v o i d s w i t h i n t h e m e t a l . T h i s , a c c o r d i n g t o V e r m i l y e a , ' 1 4 ) r e s u l t s f r o m t h e m o v e m e n t of a t o m s f r o m t h e m e t a l i n t o t h e o x i d e f r o m p o s i t i o n s o t h e r t h a n p r e f e r r e d s i t e s , e . g . , l a t t i c e - s t e p p o s i t i o n s .

T h e r e s u l t s o b t a i n e d f o r t h e r a d i o a c t i v i t y t r a c e r e x p e r i m e n t s a r e s h o w n i n F i g u r e s 7 a n d 8. F i g u r e 7 i s a m i c r o g r a p h of t h e a u t o r a d i o g r a p h of t h e n i c k e l f l u o r i d e s c a l e . T h i s m i c r o g r a p h c l e a r l y s h o w s a n a r r o w b a n d

Figure 7 MICROGRAPH OF AUTORADIOGRAPHIC EMULSION

SHOWING NICKEL-63 ACTIVITY IN NICKEL FLUORIDE SCALE

Figure 8 MICROGRAPH OF AUTORADIOGRAPHIC EMULSION

SHOWING NICKEL-63 ACTIVITY IN NICKEL OXIDE SCALE

A, original location of nickel substrate; B, nickel-nickel fluoride interface; C, nickel fluoride scale; D, darken zone in emulsion due to radioactivity; E, location of nickel fluoride-fluorine gas interface; F, original location of dental rubber mounting.

lOOfi

A, original location of nickel substrate; B, nickel-nickel oxide interface; C, nickel oxide scale; D, darkened area of emulsion due to radioactivity; E, location of nickel oxide-oxygen gas interface; F, original location of Bakelite mounting.

of activity at the posit ion of the scale-f luorine interface. The line, indi-cated by a r row E in Figure 7, locates the position of the sca le -gas in te r -face. The width of the darkened portion of the einulsion is g rea te r than the thickness of the port ion of the nickel fluoride film occupied by the r ad io -active nickel because of the d ispers ion of the beta rays in the 5-,u-thick emulsion. F r o m the location and distr ibution of the radioactivity, it can be deduced that fluorine is the migra t ing species in this react ion and that it m ig ra t e s through the nickel fluoride film to the meta l surface where it r eac t s with the nickel.

Figure 8 is a m i c r o g r a p h of an autoradiograph of the nickel oxide scale . The nickel activity is seen to penet ra te into the nickel oxide scale . The l inear penetrat ion normal to the surface of the film is as much as 70 percent of the thickness of the oxide film.

Bardeen(8) predic ted that the activity would extend to the nickel-nickel oxide interface. However, the diminution of the activity close to the interface may not be reso lved in the autoradiograph. In addition, Birchenal l ( l3) has pointed out that the expected distr ibution of radioactive t r a c e r has been found by other worke r s to drop off rapidly in the region near the meta l -oxide interface. He has postulated that this effect is due to an abrupt change in the diffusion coefficient owing to the porosi ty in the scale near the meta l -oxide interface. Poros i ty has been observed in the nickel oxide scales produced in these exper iments and could therefore account for the activity dis t r ibut ion found in Figure 8.

The resu l t s obtained in both types of m a r k e r exper iments indicate that fluorine, r a the r than nickel, m ig ra t e s through the fluoride scale dur -ing the course of the react ion. Fluorine could r each the meta l surface by g ross movement through pores and c racks in the fluoride scale or by some t r anspor t p roces s through the bulk of the sca le . Since the kinet ics of the react ion have been shown to follow a parabol ic r a t e , * it is m o r e likely that the mechan i sm involves the t r anspo r t of fluorine through the bulk of the nickel fluoride sca le . Resolution of the mode of t ransfer of fluorine from the gas phase through the fluoride scale r equ i r e s further expe r i -mental work. The evidence obtained fromi the m a r k e r exper iments for the nickel-oxygen react ion is in accord with the accepted meta l - ion diffu-sion mechan ism for that react ion.

*See Section III of this r epor t .

15

I I I . T H E K I N E T I C S O F T H E R E A C T I O N O F N I C K E L W I T H F L U O R I N E

A . M a t e r i a l s , A p p a r a t u s , a n d E x p e r i m e n t a l P r o c e d u r e

B o t h h i g h - p u r i t y n i c k e l a n d c o m m e r c i a l A - n i c k e l w e r e u s e d i n t h e s e e x p e r i m e n t s . T h e h i g h - p u r i t y n i c k e l , d e s i g n a t e d b y t h e n a m e N i v a c , w a s o b t a i n e d f r o m t h e C r u c i b l e S t e e l C o m p a n y a n d w a s p r e p a r e d by v a c -u u m m e l t i n g . A n a l y s e s of t h e N i v a c n i c k e l b y c h e m i c a l a n d s p e c t r o g r a p h i c n i e a n s i n d i c a t e d 9 9 . 9 2 p e r c e n t n i c k e l . T h e p r i n c i p a l i m p u r i t i e s , i n p a r t s p e r m i l l i o n , w e r e a s f o l l o w s : c o b a l t , 3 0 0 ; i r o n , 4 0 0 ; c a r b o n , 8 2 ; o x y g e n , 2 8 ; a n d n i t r o g e n , 3 1 . T h e p r o p e r t i e s of t h e A - n i c k e l a r e d e s c r i b e d i n S e c t i o n I I . A .

T h e f l u o r i n e u s e d i n t h e s e e x p e r i m e n t s w a s p u r i f i e d b y d i s t i l l a t i o n a n d w a s a s s a y e d by r e a c t i o n w i t h m e r c u r y . ( 1 1 ) I t w a s f o u n d t o b e 9 9 . 9 3 v / o p e r c e n t f l u o r i n e . T h e i m p u r i t i e s i n p a r t s p e r m i l l i o n a s d e t e r m i n e d b y m a s s s p e c t r o g r a p h i c a n a l y s i s of t h e r e s i d u a l g a s w e r e a s f o l l o w s : o x y g e n ,

3 9 6 ; w a t e r , 117; n i t r o g e n , 78 ; c a r b o n Fi,.;urc J d i o x i d e , 30 ; s i l i c o n t e t r a f l u o r i d e , 30 ;

a n d a r g o n , 12. APPAR\TUS FOR THE iTUDY OF THE *

KINLTICS OF THE NICKEL-FLUORINE REACTION ^^^ s y s t e m u s e d f o r t h e s e

m e a s u r e m e n t s i s s h o w n s c h e m a t i c a l l y . ' , IANT [R/Fttar.-E i n F i g u r e 9. I t c o n s i s t s of ( l ) a r e a c -

- ' t i o n v e s s e l cind t u b e f u r n a c e , (2) a m a n -r.^-j^l'^ll^t -"^'-rrr' "'' i f o l d w i t h o u t l e t s f o r v a c u u m , f l u o r i n e

I I ^-J-.^-^ , -[... s u p p l y , a n d t h e p r e s s u r e - m e a s u r i n g " ' ' ' "" "^ " ' ' ^ d e v i c e s , a n d (3) a t h e r m o s t a t t e d s e c -

j " i . t i o n c o n t a i n i n g c a l i b r a t e d v e s s e l s of wr.jf,- u^ip ^ ^ ui' - = ' d i f f e r e n t v o l u m e s . T h e v o l u m e s of

1 , .^i, a p p r o p r i a t e p o r t i o n s of t h e m a n i f o l d , .A n-r ""^ f t h e t h e r m o s t a t t e d v e s s e l s , a n d t h e

p r e s s u r e t r a n s m i t t e r s e c t i o n w e r e d e -t e r m i n e d by P V T m e a s u r e m e n t s , u s i n g a w a t e r - c a l i b r a t e d s t a n d a r d v o l u m e .

^ Fjpr ^a...r

%L:: J K E L i i - ' FL ll\lH TUBF FU^NA E - ^ I

T h e i n t e r n a l s u r f a c e s of t h e r e -a c t i o n v e s s e l s s e r v e d a s t h e n i c k e l r e -

a c t a n t . T h e v e s s e l s w e r e f a b r i c a t e d f r o m e i t h e r N i v a c s h e e t o r A - n i c k e l t u b i n g a n d s h e e t b y h e l i u m - s h i e l d e d a r c w e l d i n g . T h e v e s s e l s w e r e a b o u t 4 i n . i n l e n g t h a n d o n e i n c h in d i a m e t e r ; e a c h v e s s e l h a d a v o l u m e of a b o u t 4 7 c c a n d a n a r e a of a b o u t 95 s q c m . T h e N i v a c n i c k e l s h e e t w a s a b o u t 20 m i l s i n t h i c k n e s s a n d h a d b e e n v a c u u m a n n e a l e d ; t h e A - n i c k e l w a s u s e d a s r e c e i v e d . D u r i n g t h e f o r m i n g a n d w e l d i n g of t h e v e s s e l s , s p e c i a l c a r e w a s t a k e n to p r e v e n t c o n t a n i i n a t i o n of t h e m e t a l , a n d t h e f a b r i c a t i o n w a s b r o k e n u p i n t o s t e p s b e t w e e n w h i c h t h e s u b a s s e m b l i e s w e r e c l e a n e d a n d d e g r e a s e d . A l e n g t h of - g - - i n . - d i a m e t e r A - n i c k e l t u b i n g w a s w e l d e d t h r o u g h t h e t o p p l a t e of e a c h v e s s e l t o s e r v e a s t h e c o n n e c t i o n to t h e m a n i f o l d .

16

The reac t ion vesse l s were held in a 10-in.-long nickel cylinder which in turn fitted snugly into a 2-|--in. tubular furnace. This section of the appara tus is shown schematical ly in F igure 10. In addition to the hole dr i l led to hold the react ion ves se l s , two thermocouple wells were dr i l led in the block, one terminat ing at the level of the midpoint and the other at the bottom of the react ion vesse l . The t empera tu re of the tube furnace was controlled by means of a py romete r - ind ica to r -con t ro l l e r through a proport ional c i rcui ted Var iac . The pyrometer was actuated by the output of a ch romel -a lumel thermocouple placed near the res i s t ance winding of the tubular furnace.

F igure 10 REACTION A^ESSEL AND NICKEL BLOCK

TO MANIFOLD

.1 HOKE 413 A VALVE

SWAGELOK FITTING

NICKEL BLOCK 10 ID LONG 2 1/Zm DIAMETER

CONTROL

THERMOCOUPLE

ARGON

Plat inum-90 percent platinum, 10 percent rhodium thermocouples were used to sense the t empera ture of the react ion vesse l . A Rubicon type B potentiometer and associa ted s tandard cell and galvanometer were utilized to m e a s u r e the output of the thermocouples . Tempera ture control during a react ion period was within one degree C.

The p r e s s u r e s on the ine r t side of the nickel diaphragms of the Booth-Cromer e lec t r i ca l p r e s s u r e t r ansmi t t e r s were measured with ei ther a wel l- type m e r c u r y manometer or a U-tube manometer filled with Octoi l -S.

At the s t a r t of an exper iment the nickel ves se l was attached to the n-ianifold, evacuated., and tes ted for leaks . The evacuated vesse l was then heated to the react ion t empe ra tu r e and fluorine was admitted to a p r e s s u r e of 700 m m of Hg, At this points p r e s s u r e and time recordings were s tar ted . The changes in p r e s s u r e were r eco rded at suitable tinie in te rva ls : at y - m i n in terva ls for the f i r s t 1-2 min, at l-niin in tervals for the f i r s t half hour5 and then at gradually lengthening t ime intervals as the reac t ion slowed down. The p r e s s u r e in the sys tem was kept within 25 m m of the init ial p r e s s u r e by interi-nittent additions of fluorine as the p r e s s u r e dropped. P r e s s u r e readings during the ini t ial rapid portion of the react ion were made with a m e r c u r y manomete r . Subsequent readings were made using an Octoil-S-fi l led manometer to uti l ize i ts g rea te r sensit ivity.

F o r overnight periods., when the apparatus was left unattended, one of the ba l las t volumes was included in the react ion sys tem so that the p r e s -sure in the sys tem would not drop below the specified value. The quantity of fluorine in the react ion volume was calculated from values of the p r e s s u r e , volumesj and t empe ra tu r e s of the various sections of the apparatus involved,

B. Resul ts and Discussion

The re su l t s obtained in the nickel-f luorine kinetic exper iments with Nivac nickel over the t empe ra tu r e range from 300 to 600 C a r e shown in F igure 11, in which micrograi-ns of fluorine consumed per sq cm of nickel surface a r e plotted ve r sus the react ion time in minutes . The exper iments were run for about 2000 min at each t empera tu r e .

In F igure 12 the data a r e presented as a log-log function of the same coordinates used in F igure 11, In the construction of these plots the data for the f i r s t minute of react ion t ime were discarded, because the react ion is init ially governed by a random selection of react ion sites due to activity differences over the nickel surface . The react ion proceeds rapidly on these s i tes in the manner of a nucleation p rocess which., by subsequent outgrowth and coalescence of growth s i t e s , r e su l t s in a continuous fluoride scale over the ent i re nickel surface . In the init ial phase, the react ion is not controlled by the t r anspo r t of fluorine through a nickel fluoride b a r r i e r , as is the case once a continuous fluoride scale is p resen t over the entire nickel surface.

18

Figure 11 LINEAR PLOT OF RATE OF REACTION OF NICKEL WITH FLUORINE

IN THE TEMPERATURE RANGE FROM 300 TO 600 C

Fluor ine P r e s s u r e : Mater ia l :

700 25 mm Nivac nickel

2000

Figure 12 LOGARITHMIC PLOT OF RATE OF REACTION OF NICKEL WITH FLUORINE IN THE TEMPERATURE RANGE FROM 300 TO 600 C

Fluorine P r e s s u r e : 700 + 25 mm Mater ia l :

Nivac Nickel: 99.92% Fluor ine: 99.93%

1000 54,800

100 TIME,minutes

1000

5,480 111

54 8

19

F o r these log-log plots the r ec ip roca l s of the slopes a re the values of n in the equation w"- = kt, in which w is the fluorine consumed per sq cm of nickel surface, k is the react ion ra te constant, and t is the t ime. Values of n determined graphical ly from the plots of F igure 12 a re l isted above the appropr ia te l inear sect ions. These values indicate that the reaction initially follows a parabol ic r a t e law, but that after a period of t ime the react ion slows down, conforming to a cubic or slower ra te . The parabolic ra te constants are l is ted in Table 1, and the logari thms of these ra te con-stants a r e plotted ve r sus l / T in F igure 13. The slope of this plot yields an activation energy of 17 kca l /mo le .

Table 1

PARABOLIC RATE CONSTANTS FOR THE NICKEL-FLUORINE REACTION OVER THE TEMPERATURE

RANGE FROM 300 TO 600 C Mater ia l : Nickel, Nivac 99.92%

Fluor ine , 99.93%

Tempera tu re (C)

300 400 500 600

Value n

1.9 1.9 2.2 1.9

of Parabol ic

Rate Constant (MgFz/sq cm)Vmin

9.8 81.0

461 1860

Figure 13 ARRHENIUS PLOT OF PARABOLIC RATE

CONSTANTS FOR THE REACTION Ni + F2 - NiFa IN THE TEM-

PERATURE RANGE FROM 300 TO 600 C

13 14 15 l/T, K X 10^

600 530 400 TEMPERATURE, C

20

Resul t s obtained in exper iments with A-nickel at 400, 500, and 600 C a r e shown in F igure 14; included on the plot a r e the data for Nivac nickel at the same t e m p e r a t u r e s . F r o m these data, it is apparent that the react ion between fluorine and A-nickel is slower at a given t empera tu re than that between fluorine and Nivac nickel . This difference is g rea tes t during the init ial per iods of the reac t ions , and becomes less pronounced with t ime and at higher t e m p e r a t u r e s . This is i l lus t ra ted by the fluorine consunaption and scale thickness data at var ious react ion t imes . The scale th icknesses were calculated by use of the theore t ica l density for nickel fluoride: 4.63 g/cm^ based on X- ray data.

F igure 14 COMPARISON OF THE REACTION BETWEEN FLUORINE

AND NIVAC AND A-NICKEL IN THE TEMPERATURE RANGE FROM 400 TO 600 C

P r e s s u r e : 700 25 m m Mater ia l : NV - Nivac, 99.92% purity

AN - A-nickel , ~99.4% purity

1000 TIME, minutes

The data show that the ra te of formation of nickel fluoride scale at 600 C becomes identical for the two nickel samples at react ion t imes g rea te r than 500 min. At 500 C this leveling off of the ra te of scale for-mation does not occur until 1000 min of react ion t ime have elapsed. At 400 C it would apparently requ i re a longer react ion period than that used in these experii-nents to r each the leveling-off period. F r o m these data it can be concluded that, after a cer ta in scale thickness has been formed the continuing fluorine consumption of the sys tem will be constant and inde-pendent of the purity of the nickel.

At the p resen t t ime an explanation for the difference in react ivi ty can be at t r ibuted to two var iab les : (l) the differences in puri ty and (2) the grain size of the two types of nickel. Differences in the amounts of

the main impur i t ies in the two types of nickel, in par ts per million, a r e iron, 400 ve r sus 1000; carbon, 80 ve r sus 700; silicon, 100 ve r sus 800; and copper, 100 ve r sus 500, for Nivac and A-nickel , respect ively. Est imation of the average grain size was made using the ASTM method designated E91-51T (ASTM Standards 1952, P a r t 2, Nonferrous Metals) . In this method, mic rographs (magnification lOOX) of polished and etched samples a re com-pared with micrographs of a s tandard grain size s e r i e s . By this method, it was determined that the average gra in size of the A-nickel was 0.11 m m and that of the Nivac nickel was 0.03 mm. It is possible, therefore , that the higher init ial react ivi ty of the Nivac nickel could be due to the smal l grain size of the Nivac nickel and the consequent g rea te r grain-boundary a r ea .

A compar ison of the ra te constants at various t empera tu res could not be made for the A-nickel because of a change in the order of the r e -action with t empera tu re . This variat ion is shown in the log-log plots of F igure 15. At 400 and 500 C, the react ion appears to follow a logarithmic ra te law; at 600 C the react ion approaches a parabolic ra te law behavior. This change in order was also noted by Steunenberg et al .(l5) in a previous study of the kinetics of the nickel-fluorine reaction. The resu l t s obtained in that work and in the p resen t study a r e in good agreement , as is shown in Table 2, in which the nickel fluoride scale thicknesses formed after a react ion t ime of 1000 min at various t empera tu res a re compared. In the previous study by Steunenberg, A-nickel and commerc ia l tank fluorine of g rea te r than 99 percent purity were used.

F igure 15 THE FLUORINATION OF A-NICKEL IN THE TEMPERATURE RANGE FROM 400 TO 600 C

lOOO:

100

z g X,

10

i 1 10 100 1000

TIME mirutes

22

Table 2

NICKEL FLUORIDE SCALE THICKNESSES AFTER 1000 MIN OF REACTION TIME FOR A-NICKEL

Nickel Fluoride Scale Thickness , A Tempera tu re

(C) This Study Steunenberg et al.( 15)

400 4,400 3.800 500 8,200 9,200 600 29,000 30,000

Gas-me ta l reac t ions in which the r a t e s a r e control led by a diffusion p r o c e s s and a r e dependent on the thickness of the scale formed somet imes show a p r e s s u r e dependence of a fract ional o rder . Two exper iments at each of the following p r e s s u r e s of f luorine: 100, 350, and 700 mm Hg, were made at 500 C with Nivac nickel . Ultimate fluoride scale th icknesses obtained in these experimients after 1500 to 2000 min of react ion t ime were approxi-mately 17,000 A. The re su l t s of these react ions did not indicate a p r e s s u r e dependence of the reac t ion ra te beyond the reproducibi l i ty of the data, ap-proximately 10 percen t . Pa rabo l ic ra te constants obtained from these data a r e l i s ted in Table 3, along with the average values at each p r e s s u r e and the average of the six ra te cons tants . It is apparent from these r a t e constants that the effect of p r e s s u r e on the react ion over the range covered in this work mus t be l ess than the magnitude of the deviation between runs .

Table 3

PARABOLIC RATE CONSTANTS FOR THE NICKEL-FLUORINE REACTION AT 500 C AND FLUORINE PRESSURES OF

100, 350, AND 700 m m

Mater ia l : Nivac nickel, 99.92% Fluor ine , 99.93%

Final Scale Thickness : ~1.7 x 10* A

Parabol ic Rate Constants P r e s s u r e

(mm)

700 700

350 350 100 100

(Mg F a / sq c m ) y m i n

461 387 370 322

355 438

Average Values

424 37

346 23

396 41

Average of 6 Constants = 388 4 0

23

Work per fo rmed at the Gaseous Diffusion Plant at Oak Ridge by Hale and coworkers(2) showed the ra te for the nickel-fluorine react ion to be p r e s s u r e dependent in the case of samples having initial nickel fluoride sca les of about 2.5 x 10^ A in th ickness . The data were used to derive the constants in the following equation:

dx/dt = kp"^

in which dx/dt is the ra te of growth of the fluoride scale , k is the ra te con-stant, and p is the p r e s s u r e . F r o m the slope of a log-log plot of dx/dt ve r sus p for their data at 600 C, a value of n of 0.87 was obtained.

These m e a s u r e m e n t s were repeated by us with both A-nickel and Nivac nickel samples having initial nickel fluoride scales of about 2.5 X 10^ A in th ickness . Our data along with values obtained from the Oak Ridge data by interpolat ion a r e l is ted in Table 4. The data obtained for A-nickel a r e plotted in Figure 16. F r o m the data l is ted in Table 4, it can be seen that our r e su l t s for A-nickel compare closely with those obtained at Oak Ridge. However, the Nivac nickel resu l t s a re higher than those ob-tained for A-nickel . In Figure 17, the rate of change in the thickness of the film is plotted ve r sus the p r e s s u r e of fluorine in a tmospheres as a log-log plot of the data from this study for Nivac nickel and for interpolated points obtained from the Oak Ridge work. F r o m the slopes of these curves , a value of n of 0.55 was obtained for this work and a value of n of 0.87 was obtained for the Oak Ridge work.

Table 4

THE E F F E C T OF PRESSURE ON THE RATE OF BUILDUP OF A NICKEL FLUORIDE SCALE AT 600 C

Initial Scale Thickness : ~2.5 x 10^ A Equation: dx/dt = kp"-

Rate of Increase of Scale Thickness , dx/dt , {jig Fg/sq cm) /min

P r e s s u r e (atm)

0.96 0.46 0.13

Nivac

1.20 0.78 0.11

This Study

A-Nickel

0.13 0.082 0.038

Oak Ridge, A-Nickel(2)

0.17 0.085 0.030

24

Figure 16 PRESSURE DEPENDENCE OF NICKEL-FLUORINE REACTION

Tempera tu re : 600 C Initial NiFg

Scale Thickness: ~2.5 x 10^ A

200 300 TIME, minutes

Figure 17 RATE OF CHANGE OF SCALE THICKNESS AS A

FUNCTION OF FLUORINE PRESSURE

O THIS STUDY

A OAK RIDGE AECD-4292

I I I I

Tempera tu re : 600 C Initial Scale Thickness: 2.5 x 10^ A

Equation log dx/dt = log k + n log p

PRESSURE FLUORINE, olm

25

IV. SUMMARY

Evidence obtained from two exper imental approaches has been presen ted for the mechan ism of the nickel-fluorine react ion. In one ap -proach the isotope nickel-63 was used as a s e l f -marke r , and the d i s t r i -bution of the beta activity of the nickel-63 in the scale indicated the species , nickel or fluorine, that migra ted during the react ion. In the second or impinging scale technique, the cha rac te r of the interface formed when sca les from opposing nickel surfaces a re made to grow against one another indicated the migra t ing spec ies . The validity of the miethod was checked by performing s imi la r exper iments with the nickel-oxygen s y s -tem, a sys tem for which the react ion mechanism is known. In this sys tem, the react ion proceeds via migra t ion of nickel ions through the oxide scale to the oxide-scale interface.

In the isotopic t r a c e r exper iments , nickel-63 was plated on the su r -faces of nickel coupons which were then fluorinated or oxidized. The r e -acted specimens were then mounted in Bakelite and sectioned normal to the surface of the sca le . An autoradiograph was then taken and, after development, was mounted on a microscope slide. The autoradiograph repl icated the surface of the speciinen so that an unambiguous identifica-tion of the m e t a l - s c a l e and sca l e -gas interfaces could be made. In the nickel-f luorine exper iments , the nickel-63 activity was found concentrated at the fluoride scale-f luor ine interface, thus indicating that the react ion miechanism involved the migra t ion of the fluorine through the nickel fluoride scale to the s ca l e -gas interface. A s imi la r experimient with the nickel-oxygen sys tem showed a dis tr ibut ion of the nickel-63 activity such as would be expected for a mechan i sm in which nickel migra ted through the growing oxide scale to the nickel-nickel oxide interface. The resu l t s obtained in the nickel-oxygen exper iment a r e in accord with the accepted mechanism for this react ion.

In the impinging scale exper iments , react ion specimens were p r e -pared by welding together two nickel coupons along a common edge, so that the opposing surfaces were separa ted by only a fraction of a mi l l ime te r . The spec imens , after react ion, were mounted in Bakelite and sectioned to expose the scales held between the opposing nickel faces. If the two op-posing sca les a r e fused into a single, continuous scale , meta l migra t ion is indicated with react ion occurr ing at the sca le -gas interface. If, however, the two sca les a re not fused into a single, continuous scale and a definite interface exis ts between them, nonmetal migrat ion is indicated, with r e a c -tion occurr ing at the s ca l e -me ta l interface. In the fluoride impingement exper iments , the p resence of an interface between the two fluoride scales indicated the migra t ion of the nonmetal , fluorine. In the nickel oxide im-pingement exper iments , the fusion of the two scales into one continuous scale indicated migra t ion of the me ta l , nickel.

Although these exper iments showed that the mechan ism of the nickel -fluorine react ion involves the migra t ion of fluorine through the growing fluoride scale to the m e t a l - s c a l e interface, they did not indicate the mode of t r anspor t of the fluorine. Two poss ibi l i t ies exist : the fluorine mig ra t e s to the m e t a l - s c a l e interface by g ross movement through pores and c racks in the fluoride sca le , or by some t r anspo r t p r o c e s s through the bulk of the scale . Since the kinet ics of the react ion have been shown to follow a p a r a -bolic rate law, it is m o r e likely that the mechanism involves the t r anspor t of fluorine through the bulk of the nickel fluoride sca le .

The kinet ics of the nickel-f luorine react ion were m e a s u r e d over the t empera tu re range from 300 to 600 C with Nivac, a high-puri ty nickel, and commerc ia l A-nickel , A manomet r i c technique was employed and the r e -actions were per formed under i sobar ic conditions. The kinet ics of the react ion between Nivac nickel and fluorine were found to obey a parabol ic rate law, with react ion ra te constants of 9.8, 81.0, 461, and I860 (jJ-gFz/ sq cm Ni) / m i n at 300, 400, 500, and 600 C, respect ively . An activation energy for the react ion of 17 kca l /mo le was calculated from the value of the slope of an Arrhenius plot of the data. Comparison of the t empera tu re dependence of the ra te constants obtained for the react ion between A-nickel and fluorine with those for the reac t ion between Nivac nickel and fluorine could not be made as the ra te law compliance in the case of A-nickel changed with t e m p e r a t u r e , from logar i thmic at 400 and 500 C to parabol ic at 600 C. The ra te of react ion was , however, higher for Nivac than it was for A-nickel . A sma l l e r c rys t a l gra in size for the Nivac nickel might account for its higher react ivi ty . The parabol ic react ion ra te constants for the Nivac nickel did not show a p r e s s u r e dependence g r e a t e r than the uncertainty for an individual constant, which was 10 percent , over the p r e s s u r e range from 100 to 700 m m of Hg. However, for samples having an initial fluo-ride scale of about 10^ A in thickness the r a t e s obtained were found to be dependent on a fractional power of the p r e s s u r e of fluorine. The react ion ra te of Nivac nickel was found to be dependent on the 0.55 power of the p r e s s u r e , whereas that for A-nickel was about 0.87 power of the p r e s s u r e which was confirmatory of the p r e s s u r e dependence found for A-nickel by worke r s at Oak Ridge,(2)

V. ACKNOWLEDGMENTS

The authors wish to axknowledge the helpful suggestions and advice given during the course of this work of J. G Schnizlein, L. Leibowitz, and R. K. Steunenberg. In par t icu lar we wish to thank M, D. Adams for his considerable advice and ass i s t ance in the autoradiographic p roces s .

VI. BIBLIOGRAPHY

1. Steindler, M. J . , and Vogel, R. C , Corrosion of Mater ia ls in the P r e s e n c e of Fluorine at Elevated Tempera tu re s , ANL-5662 (Jan 1957).

2. Hale, C. F . , et a l . , High Tempera tu re Corrosion Study, Interixn Report for the Pe r iod November 1958 through May 1959, AECD-4292 (July 28, 1959).

3. Jackson, R, B. , Corros ion of Metals and Alloys by Fluorine, NP-8845 (I960).

4. White, E. L., and Fink, F . W., Mater ia l s of Construction for Handling Fluor ine , Proceedings of the Propel lant Thermodynamics and Handling Conference, Ohio State Exper imenta l Station Special Report 12 (June I960).

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