UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

An investigation of the penetration of thin aluminum oxide films by liquid bismuth Allday, William John 1961

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-UBC_1961_A7 A5 I6.pdf [ 5.59MB ]
Metadata
JSON: 831-1.0105831.json
JSON-LD: 831-1.0105831-ld.json
RDF/XML (Pretty): 831-1.0105831-rdf.xml
RDF/JSON: 831-1.0105831-rdf.json
Turtle: 831-1.0105831-turtle.txt
N-Triples: 831-1.0105831-rdf-ntriples.txt
Original Record: 831-1.0105831-source.json
Full Text
831-1.0105831-fulltext.txt
Citation
831-1.0105831.ris

Full Text

AN INVESTIGATION OF THE PENETRATION OF THIN ALUMINUM OXIDE FILMS BY LIQUID BISMUTH.  by  WILLIAM JOHN ALLDAY  A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE  i n the Department of MINING AND METALLURGY  We a c c e p t t h i s thesis'" as conforming  t o the  s t a n d a r d r e q u i r e d from c a n d i d a t e s f o r t h e degree o f MASTER OF APPLIED SCIENCE.  Members Mining  o f the Department o f and M e t a l l u r g y .  THE UNIVERSITY OF BRITISH COLUMBIA April,  196l.  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of  the r e q u i r e m e n t s f o r an advanced degree a t the  University  o f B r i t i s h C o l u m b i a , I agree t h a t the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r r e f e r e n c e and  agree t h a t p e r m i s s i o n f o r e x t e n s i v e f o r s c h o l a r l y purposes may  study.  I further  c o p y i n g of t h i s  be g r a n t e d ' b y the Head o f  Department o r by h i s r e p r e s e n t a t i v e s .  thesis my  I t i s understood  t h a t c o p y i n g or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l not  Department o f  be a l l o w e d w i t h o u t my w r i t t e n  M i n i n g and  Metallurgy  The U n i v e r s i t y of B r i t i s h Vancouver $, Canada. Date  April k,  1961  Columbia,  permission.  - i -  ABSTRACT  The  p e n e t r a t i o n of t h i n aluminum oxide f i l m s by l i q u i d b i s m u t h  s t u d i e d between 35°  and  500°C.  A c o r r e l a t i o n was  sought between t h e type  t h i c k n e s s of the oxide f i l m , and the time and n a t u r e a n i c a l and  e l e c t r o p o l i s h e d , and a n o d i z e d  exposed t o l i q u i d bismuth e i t h e r by measuring the c o n t a c t angle  was  o f the a t t a c k .  and  Mech-  f i l m s o f d i f f e r e n t t h i c k n e s s e s were  immersing a p l a t e i n the l i q u i d  or by m e l t i n g a drop o f bismuth on a  and  specific  area of a p l a t e .  E l e c t r o p o l i s h e d s u r f a c e s had no r e s i s t a n c e t o a t t a c k by the b i s m u t h . P i t t i n g and anodized allowed  edge a t t a c k o c c u r r e d w i t h a l l o t h e r s u r f a c e p r e p a r a t i o n s .  f i l m s often separated  The  from the aluminum under t h e r m a l s t r e s s e s  the b i s m u t h t o s p r e a d under the f i l m ,  and  sometimes removing i t e n t i r e l y .  Attempts were- made t o c o n t r o l the number and n a t u r e  of defects i n  the oxide f i l m , but the d i f f i c u l t y of t h i s i s shown by the s c a t t e r i n the results.  Wo.attack on aluminum oxide i t s e l f i s l i k e l y and no d i f f u s i o n bismuth through.the o x i d e was  The  c o n c l u s i o n was  f o u n d a t t h e temperatures u s e d .  r e a c h e d t h a t the bismuth p e n e t r a t e d  f i l m o n l y a t p o i n t s where t h e r e was i m p u r i t y oxide  of  the  oxide  a h i g h c o n c e n t r a t i o n i n the f i l m o f some  (such as n i c k e l or copper o x i d e s ) t h a t r e a c t s w i t h b i s m u t h .  - i i-  ACKNOWLEDGEMENT  The  author i s i n d e b t e d  t o P r o f e s s o r W. M. Armstrong, Dr. J . B. Raynor  and Mr. M. J . F i n l a y s o n f o r t h e i r s u p e r v i s i o n and encouragement, and t o Mr.  R. B u t t e r s  f o r h i s t e c h n i c a l advice  and a s s i s t a n c e .  The many v a l u a b l e  d i s c u s s i o n s w i t h Dr. A. C. D. C h a k l a d e r and Mr. K. G. D a v i s a r e a l s o  grate-  f u l l y acknowledged.  The work was f i n a n c e d b y R e s e a r c h Grants DRB p r o v i d e d b y t h e Defence R e s e a r c h B o a r d o f Canada.  7510-32  and DRB  7510-36  - iii  TABLE OF CONTENTS  Page I.  II.  III.  IV.  INTRODUCTION  .  1 1  A.  Uses o f L i q u i d M e t a l s  B.  Corrosion by L i q u i d Metals  C.  Previous  I n v e s t i g a t i o n s on L i q u i d Bismuth  5  D.  Previous  Work on T h i n Oxide F i l m s  8  E.  S p e c i f i c Aims o f t h e P r e s e n t  EXPERIMENTAL  . . . . . . . . . .  on Aluminum  Investigation  P a r t 1.  . . .  3  13  Ik  A.  P r o p e r t i e s o f L i q u i d Bismuth  Ik  B.  Laboratory  l6  C.  D e s c r i p t i o n o f Apparatus  20  D.  E x p e r i m e n t a l Procedure  28  E.  Theory  29  F.  Analysis of Results  31  H a n d l i n g o f L i q u i d Bismuth  .  EXPERIMENTAL • P a r t 2  kO  A.  D e s c r i p t i o n o f Apparatus  kO  B.  E x p e r i m e n t a l Procedure  kl  C.  Analysis of Results  k2  D.  Discussion of Results  V7  EXPERIMENTAL  Part 3  .  52  A.  D e s c r i p t i o n o f Apparatus  52  B.  E x p e r i m e n t a l Procedure  55  C.  Analysis of Results  56  -  - iv -  Page Vo  VI.  VII.  VIII.  CONCLUSION  . o o . o . . . . . . '. o . . . . . . . „ . . . „ .  RECOMMENDATIONS FOR FURTHER WORK  APPENDICES  BIBLIOGRAPHY  6l  . . . . . . . . . . . . . . .  6h  . . . . . . . . . . . . . . . . . . . . . . . . . .  65  . . . . . . . . . . . . . . . . . . . . . . . . .  71  - V  -  FIGURES  No.  Page  1=  S u r f a c e t e n s i o n o f l i q u i d bismuth, under d i f f e r e n t atmospheres  2.  V a r i a t i o n o f e q u i l i b r i u m , c o n t a c t a n g l e w i t h temperature f o r t i t a n i u m and z i r c o n i u m  Rate o f oxide f i l m growth on aluminum  4.  Growth o f oxide on aluminum.  5o  F i l m growth i n ammonium t a r t r a t e e l e c t r o l y t e  6.  Water vapour a d s o r p t i o n b y m o l e c u l a r s i e v e s  7o  Magnetic b a l a n c e assembly  8.  Magnetic b a l a n c e c i r c u i t diagram  9.  C a l i b r a t i o n o f magnetic b a l a n c e  . . . . . . . .  10.  Drawing o f t h e g l a s s apparatus  . . . . . . . . . . . . .  11.  P l a t e attachment  12.  F o r c e s on t h e p l a t e i n l i q u i d b i s m u t h  13«  T y p i c a l p l o t o f c o n t a c t a n g l e v time  14.  W e t t i n g b e h a v i o u r o f A l c a n 2S  15.  Wetting behaviour of mechanically p o l i s h e d  1 6 .  Mechanically polished  1 7 .  Mechanically polished  18.  V e r t i c a l s e c t i o n o f p l a t e 1 9 showing bismuth under t h e o x i d e  19.  S e c t i o n o f p l a t e 3 3 showing p i t t i n g and i n t e r g r a n u l a r a t t a c k  2 0 o  Plates  / 2 1 . 22.  . . . . . . . . . . . . .  1 0  . . . . . . . . . . . . . . . . . .  1 0  . „ . „ . . . . .  1 2  . . „ . . . « . . .  1 8 2 1  . . . . . . . . . . . . . . . . . . . . .  2 3  . . . . . . . . . . . . . . . . . . . . . . . . . .  24 .  2 3  25 2.8  . . . . . . . . . . . . . . . . . . . . . . .  and  2 7  6  7  . . . . . . . . . . . . . . . . . .  3=  2 4 ,  .  3 0 .  3 4 3 6  . . . . . . . . . . .  3 7  9 9 - 9 8 $  aluminum a f t e r . i m m e r s i o n i n b i s m u t h  3 8  9 9 » 9 8 $  aluminum a f t e r immersion i n bismuth  4 3  9 9 « 9 8 $  Aluminum  a f t e r immersion i n l i q u i d b i s m u t h a t  .  400°C.  P l a t e s 25, 2 1 and 1 2 a f t e r immersion i n l i q u i d b i s m u t h . . . . .  4 4  46 46  P l a t e 3 2 a f t e r immersion i n l i q u i d bismuth f o r 2 0 minutes a t ^ 0 0 ^ 0  o  o  o  o  o  o  o  o  o  o  o  o  o  ©  o  o  »  e  c  »  o  o  o  a  o  *  5 ^  - vi No.  Page  23o  Section of p l a t e 3 2 ,  24.  P a r t i a l s e c t i o n of tube furnace  25.  Section of bismuth drop, showing general shape  260  Defect i n oxide f i l m on p l a t e D2 a f t e r penetration by l i q u i d bismuth „ . . . . . . . .  showing a defect I n the oxide l a y e r . .  5 3  . . . . . . . . . . . . . .  0  0  .  0  ......  .  0  0  .  .  .  5 0  „  5 6  5 9  - vii -  TABLES No. I. II. III.  Page Analysis  o f Bismuth  Physical Properties S o l u b i l i t y of  . . . . . . . . . . . . . . . . . . . . o f Li.quid. Bismuth  lh 15  . . . . . . . . . . .  Bi203 I n L i q u i d Bismuth . . . .  . . . . . . .  .  15  IV.  A n a l y s e s o f Aluminum Used . . . . . . . . . . . . . . . . . .  2.7  V.  Sample C a l c u l a t i o n o f C o n t a c t A n g l e . . . . . . . . . . . . .  33  M  INVESTIGATION OF THE  PENETRATION OF THIN  ALUMINUM OXIDE FILMS BY LIQUID BISMUTH  I.  INTRODUCTION  W i t h "the coming of n u c l e a r power, i n t e r e s t has o f l i q u i d metals  as h e a t - t r a n s f e r media.  The metals  grown i n the  use  considered u s e f u l f o r  t h i s purpose a r e t h o s e w i t h m e l t i n g p o i n t s below 660°C, and i n c l u d e aluminum, bismuth, assium,  cadmium, g a l l i u m , l e a d , l i t h i u m , magnesium, mercury, p o t -  sodium, t i n and z i n c , and the sodium-potassium and  eutectic  lead-bismuth  alloys.  The use of l i q u i d metals may t h e y c o r r o d e t h e s o l i d metals  be r e s t r i c t e d by'the  i n c o n t a c t w i t h them.  e x t e n t t o which  To date most o f t h e i n -  v e s t i g a t i o n s i n t h i s f i e l d have been c o n c e n t r a t e d on sodium, p o t a s s i u m their alloys.  Bismuth was  i t s i n c r e a s i n g importance.  and  chosen f o r t h e p r e s e n t i n v e s t i g a t i o n because o f I t was  decided to study i t s c o r r o s i v e a c t i o n  aluminum as t h i s m e t a l i s w i d e l y used i n e x i s t i n g n u c l e a r r e a c t o r s as a  on con-  taining material.  A.  Uses o f L i q u i d  Metals  P r i o r t o the advent  o f n u c l e a r power, sodium was  the o n l y l i q u i d  m e t a l used w i t h any s u c c e s s , w i t h the e x c e p t i o n of the G e n e r a l Company's use, i n 1922,  o f mercury vapour, i n p l a c e o f steam, t o i n c r e a s e t h e  e l e c t r i c power g e n e r a t i n g e f f i c i e n c y o f turbines- -.?^„ 1  s i n c e 1928  Electric  t o c o o l v a l v e s i n a i r c r a f t engines^,  Sodium has b e e n u s e d  c o r e s f o r magnesium d i e c a s t -  i n g , and f o r many o t h e r a p p l i c a t i o n s i n v o l v i n g h e a t - t r a n s f e r a t h i g h temperatures.  I n 19^3,  the Dow  C h e m i c a l Company o p e r a t e d a system c o n t a i n i n g  l i q u i d sodium and r e c o v e r e d as much as one  and a h a l f m i l l i o n Btu/hr  (440kw) .  - 2  L i q u i d metals have v a r i o u s a p p l i c a t i o n s i n n u c l e a r r e a c t o r s .  -  As  h e a t - t r a n s f e r media, whether u s e d as s t a t i c or dynamic c o o l a n t s , l i q u i d m e t a l s have the advantage  o f good t h e r m a l c o n d u c t i v i t y , s t a b i l i t y under c o n d i t i o n s o f  r a d i a t i o n and h i g h temperature, and low vapour p r e s s u r e ; u s e d as a f u e l  carrier,  whether as a s o l v e n t or d i s p e r s a n t o f the f u e l , l i q u i d m e t a l s are s u i t a b l e f o r continuous p r o c e s s i n g ; t h e y p r e s e n t no problems possess good h e a t - t r a n s f e r p r o p e r t i e s . b l a n k e t s and as r a d i a t i o n s h i e l d s . Alamos f a s t r e a c t o r . o f hours i n the EBR  NaK,  o f d i m e n s i o n a l s t a b i l i t y and t h e y  They a r e a l s o s u i t a b l e f o r use i n b r e e d e r  Mercury was  a sodium-potassium  u s e d as the c o o l a n t i n the Los  a l l o y , has b e e n u s e d f o r thousands  (Experimental Breeder R e a c t o r ) .  the SIR, the EBR-II, the SRE  Sodium i s t h e c o o l a n t f o r  (sodium g r a p h i t e ) and i n G r e a t B r i t a i n f o r t h e  Dounreay e x p e r i m e n t a l f a s t b r e e d e r ' r e a c t o r o f the U. K. A. E. A.  Bismuth  been p r o p o s e d f o r the LMFR ( L i q u i d M e t a l F u e l R e a c t o r ) power b r e e d e r . interested i n the p o s s i b i l i t i e s  has  Russia i s  of bismuth-lead a l l o y s .  N u c l e a r r e a c t o r s i n which l i q u i d sodium i s u s e d s u f f e r from some disadvantages'^: a)  The e f f i c i e n c y o f the s o l i d uranium f u e l rods i n t h e r e a c t o r  will  u l t i m a t e l y decrease as f i s s i o n proceeds and f i s s i o n p r o d u c t s accumulate . b)  A h i g h e r o p e r a t i o n a l temperature would be advantageous  f o r higher  h e a t - t r a n s f e r e f f i c i e n c y and t h i s can o n l y be o b t a i n e d i f a c o o l a n t o f h i g h e r b o i l i n g p o i n t i s used. T00°C  i s 100  The vapour p r e s s u r e o f sodium a t  ramJ.  I f the uranium f u e l and the f i s s i o n p r o d u c t s were s o l u b l e i n a l i q u i d o f h i g h b o i l i n g p o i n t , the above d i s a d v a n t a g e s would be e l i m i n a t e d .  Much work  has been done on systems where a continuous c y c l e o f f u e l , d i s s o l v e d i n a l i q u i d ,  - 3 -  passes through the c o r e o f t h e r e a c t o r and t h e n through some form o f c o u n t e r c u r r e n t e x t r a c t i o n p r o c e s s t o remove the f i s s i o n p r o d u c t s . tities  A d d i t i o n a l quan-  o f f i s s i l e m a t e r i a l can he added a t i n t e r v a l s and c o n c e n t r a t i o n s are  e a s i l y c o n t r o l l e d , thus g i v i n g optimum e f f i c i e n c y . o n l y l i q u i d bismuth material.  fulfils  Of the p o s s i b l e s o l v e n t s ,  t h e s e c o n d i t i o n s and i s , i n f a c t , almost t h e i d ^ . a l  L i q u i d m e t a l f u e l l e d r e a c t o r s have been d e s c r i b e d i n d e t a i l by  Frnst  8 Q and o t h e r s ' . B.  C o r r o s i o n by L i q u i d Metals  L i q u i d bismuth o n l y m e t a l l i c elements  i s one o f t h e most v e r s a t i l e o f a l l s o l v e n t s .  t h a t can be r e g a r d e d as i n s o l u b l e b e l o v 600°C are  b e r y l l i u m , molybdenum, t a n t a l u m and t u n g s t e n .  T h i s r a i s e s obvious  so f a r as c o n t a i n i n g v e s s e l s f o r l i q u i d b i s m u t h  are  problems  concerned.  I t i s p r o b a b l y t r u e t o say t h a t any l i q u i d m e t a l w i l l wet  The  completely  any s o l i d m e t a l p r o v i d e d t h a t t h e r e i s n o t h i n g to p r e v e n t t r u e m e t a l - t o -  m e t a l c o n t a c t a t the l i q u i d m e t a l / s o l i d m e t a l i n t e r f a c e .  A l l previous  exper-  i e n c e i s i n agreement w i t h t h i s assumption b u t i t i s d i f f i c u l t t o v e r i f y completely"^.  I n a l l p r a c t i c a l c a s e s , the p r e s e n c e o f an o x i d e f i l m on the  s o l i d m e t a l w i l l p r e v e n t immediate w e t t i n g .  Corrosion i s prevented  if:-  a)  the s o l i d m e t a l does not d i s s o l v e i n the l i q u i d  b)  an impervious b a r r i e r can be i n t r o d u c e d which p r e v e n t s c o n t a c t between the l i q u i d m e t a l and the s o l i d m e t a l .  metal.  T h i s can e i t h e r be  the  o x i d e o f t h e s o l i d m e t a l or a l a y e r o f a compound such as z i r c o n i u m nitride.  F o r example, i n the l i q u i d b i s m u t h - s t e e l system,  Z i r c o n i u m d i s s o l v e d i n t h e bismuth  250 p.p.m.  r e a c t s w i t h the n i t r o g e n i n the  s t e e l f o r m i n g a hard, i m p e r v i o u s , p r o t e c t i v e f i l m o f z i r c o n i u m n i t r i d e on the s t e e l . d i s s o l v i n g i n the  T h i s p r e v e n t s the i r o n i n t h e s t e e l  bismuth^.  from  - k C o r r o s i o n appears t o o c c u r o n l y when w e t t i n g t a k e s p l a c e . degree o f w e t t i n g i s determined b y t h e f o l l o w i n g a)  The  factors:-  The s o l u b i l i t y o f t h e s o l i d m e t a l i n t h e l i q u i d m e t a l , e.g.  copper  i s w e t t e d by bismuth, and i s s o l u b l e t o the e x t e n t o f 8 atomic %>  a t 500°C b)  1 1  >  1 2  .  A t t a c k on m e t a l s o f v e r y low s o l u b i l i t y i n l i q u i d b i s m u t h ( s u c h as niobium) may be i n c r e a s e d by a l l o y i n g w i t h a m e t a l t h a t i s s o l u b l e -1  i n ' b i s m u t h (copper., f o r c)  o  example)  .  I n t e r m e t a l l i c compound f o r m a t i o n a t t h e i n t e r f a c e , e.g. z i n c i s w e t t e d b y sodium a t a l l temperatures above the m e l t i n g p o i n t o f sodium 1k  be-  cause o f t h e f o r m a t i o n o f the compound NaZn^c, d)  The a b i l i t y o f the l i q u i d m e t a l atoms t o d i f f u s e t h r o u g h the o x i d e f i l m on t h e s o l i d m e t a l .  T h i s i s t h e mechanism p o s t u l a t e d b y I b e r s o n ^ ^  f o r t h e w e t t i n g o f c a l c i u m b y sodium. is e)  The s i z e o f the sodium  atom  such t h a t i t c o u l d pass t h r o u g h t h e c a l c i u m o x i d e l a t t i c e .  A d d i t i o n of an element t o the l i q u i d m e t a l t o promote w e t t i n g , e.g. i r o n i s r e a d i l y w e t t e d b y sodium i f 0.1  wt.%  c a l c i u m i s added - t h i s  i s because the o x i d e s of i r o n a r e r e d u c e d more e a s i l y b y c a l c i u m t h a n b y sodium-^.  ;  I t w i l l be seen t h a t the v a l u e o f l i q u i d b i s m u t h i n t h e f i e l d o f n u c l e a r r e a c t o r s i s not so much as a c o o l a n t , b u t as a s o l v e n t f o r many elements. From t h i s ,  i t i s apparent t h a t the s u r f a c e p r o p e r t i e s o f bismuth, the i n t e r -  a c t i o n s between l i q u i d b i s m u t h and s o l i d metals a t the s o l i d / l i q u i d  interface,  and the i n f l u e n c e o f o x i d e f i l m s a t t h i s i n t e r f a c e , are a l l o f importance i n the  study of c o r r o s i o n by l i q u i d bismuth.  C.  P r e v i o u s I n v e s t i g a t i o n s on L i q u i d  Bismuth  Many measurements o f the s u r f a c e t e n s i o n o f l i q u i d bismuth have been made from 1868  t o the p r e s e n t time, u s i n g a v a r i e t y o f methods i n c l u d i n g drop  weight, maximum b u b b l e p r e s s u r e , and du Wquy r i n g , under vacuum and  atmospheres  o f c a r b o n d i o x i d e , hydrogen, and n i t r o g e n , and o b t a i n i n g v a l u e s o f the s u r f a c e t e n s i o n o f 465  t o 269  dynes/cm.  Raynor"^  c a r r i e d out a s u r v e y o f p a s t exper-  iments, and determined a new v a l u e u s i n g the drop volume method w i t h c o r r e c t i o n f a c t o r s by H a r k i n s and B r o w n ^ .  Raynor  obtained a value f o r the surface t e n s i o n  o f l i q u i d bismuth o f 378.0 dynes/cm. a t 300°C and a temperature c o e f f i c i e n t o f  -0,069 dynes/cm/°C.  No  v a r i a t i o n o f t h e v a l u e o f t h e s u r f a c e t e n s i o n or the  temperature c o e f f i c i e n t was  f o u n d when atmospheres  o f argon, n i t r o g e n , hydro-  gen or carbon d i o x i d e were used i n p l a c e o f a vacuum (see F i g u r e  A comprehensive  l) ^. 1  s t u d y o f t h e w e t t i n g b e h a v i o u r o f a number o f t r a n s -  i t i o n element metals b y l i q u i d bismuth was u n d e r t a k e n by R a y n o r ^ u s i n g t h e 1  Wilhelmy v e r t i c a l p l a t e t e c h n i q u e .  The w e t t i n g o f the f o l l o w i n g metals  was  studied;a)  T i t a n i u m and z i r c o n i u m . W e t t i n g o c c u r r e d a t 650 and 550°C i v e l y (see F i g u r e 2) and was  respect-  governed b y t h e a b i l i t y o f the o x i d e  f i l m t o d i s s o l v e i n the s o l i d m e t a l thus e x p o s i n g m e t a l atoms f o r d i r e c t contact with bismuth. b)  Vanadium, niobium and t a n t a l u m .  Won-wetting c o n d i t i o n s  predominated  due t o t h e r e s i s t a n c e o f t h e m e t a l o x i d e t o breakdown b y l i q u i d  bis-  muth.  and  W e t t i n g o f niobium and t a n t a l u m was  o f vanadium a t 6^0°C^  }  r e p o r t e d a t 1000°C-'-^  b u t no s u g g e s t i o n s were made as t o the mech-  anism. c)  Iron.  W e t t i n g o c c u r r e d a t 500°C by a p r o c e s s i n v o l v i n g the t r a n s -  f o r m a t i o n of t h e s u r f a c e o x i d e s from Fe,0), t o FeO.  FIGURE 1. S u r f a c e t e n s i o n o f l i q u i d bismuth under d i f f e r e n t atmosph  d)  Cobalt.  S o l u t i o n o f c o b a l t i n bismuth, was  p r e v e n t e d "by the  oxide  f i l m which a c t e d as a b a r r i e r t o w e t t i n g . e)  N i c k e l and copper were wetted r e a d i l y due t o the r e d u c t i o n o f t h e i r surface oxides by  bismuth.  A s i m i l a r study t o Raynor's has been c a r r i e d out b y Iberson^-5 on t h e s u r f a c e and i n t e r f a c i a l p r o p e r t i e s o f ition  liquid  sodium a g a i n s t s o l i d t r a n s -  metals.  Much r e s e a r c h has been undertaken  on l i q u i d bismuth i n c o n j u n c t i o n  w i t h i t s a n t i c i p a t e d use i n l i q u i d m e t a l f u e l r e a c t o r s . s t u d i e d were t h e f o r m a t i o n o f i n t e r m e t a l l i c  Among the problems  .compounds i n l i q u i d bismuth  20 21 p a r t i c u l a r l y w i t h the f u e l elements uranium and t h o r i u m22 ' o s i o n o f s t e e l s i n l i q u i d bismuth, b o t h i n i s o t h e r m a l and o s i o n o f s t e e l s i n l i q u i d bismuth, b o t h systems i n v o l v i n g mass transfer^-* D.  -  ,  corr, and the non-isothermal  >}  P r e v i o u s Work on T h i n Oxide F i l m s on Aluminum  The  oxide f i l m on aluminum has been f o u n d t o be v e r y p r o t e c t i v e  a g a i n s t most forms o f c o r r o s i v e a t t a c k f o r a number o f reasons Gulbransen  summarized by  and Wysong^^ _ :  a)  t h e o x i d e / m e t a l volume r a t i o i s g r e a t e r t h a n  b)  the o x i d e i s v e r y s t a b l e thermodynamically  one.  w i t h r e s p e c t t o decomp-  o s i t i o n , r e d u c t i o n and s o l i d phase r e a c t i o n s w i t h o t h e r metals f r e e energy  of formation of  (the  AI2O3 a t 500°C i s -227 K c a l s per mole o f  26 O2 of c)  , o n l y l i t h i u m , magnesium, and c a l c i u m have lower f r e e  energies  formation)  t h e r e l a t i v e l y h i g h m e l t i n g p o i n t (2015°C) and b o i l i n g point- (2980°C) of the oxide.  - 9 d)  r e l a t i v e l y few o x i d e s t r u c t u r e s may  form.  Al^O-^ i s the o n l y  stable  o x i d e a t o r d i n a r y temperatures.  I t has been observed f r e q u e n t l y ^7-31  t h a t the v e r y f i r s t  oxide f i l m  formed on aluminum exposed t o a i r a t room temperature i s amorphous, a p p a r e n t l y c o n s i s t i n g o f an aggregate o f groups o f two m o l e c u l e s o f A l g O ^ ^  jprom the  2  w i d t h o f the d i f f u s e bands o b t a i n e d from e l e c t r o n d i f f r a c t i o n by t h i n aluminum o x i d e f i l m s , H a r r i n g t o n and Welson^5 c a l c u l a t e d t h a t the g r a i n s i z e o f the o f i l m as formed, i f c r y s t a l l i n e , was o f the o r d e r o f 12A, l e s s than t w i c e the o edge o f the u n i t c e l l o f y-Al203 (7.90  A).  There i s l i t t l e  d i f f e r e n c e between  an amorphous m a t e r i a l and a c r y s t a l l i n e m a t e r i a l o f t h i s g r a i n  size.  I n d r y a i r a t room temperature the o x i d a t i o n r a t e o f aluminum i s i n i t i a l l y v e r y h i g h b u t r a p i d l y l e v e l s o f f (see F i g u r e 3 ) . f i l m growth  stops a f t e r a month a t a t h i c k n e s s o f  X.  Hass ^  s t a t e s t;hat  2  However, V e r n o n ^  found  t h a t when the p r i m a r y f i l m on aluminum had c e a s e d t o t h i c k e n , sudden b r e a k s occ u r r e d i n the weight-increment/time curve (see F i g u r e k).  He p o s t u l a t e d t h a t  t h e y a r e caused by the o c c u r r e n c e o f c r a c k s or f i s s u r e s i n the p r i m a r y f i l m , exposing f r e s h aluminum s u r f a c e f o r o x i d a t i o n .  Measurements o f t h e f i n a l t h i c k n e s s o f the o x i d e f i l m formed on a l -  o urainum a t room temperature v a r y between 20 A and 100  o 27-30,37 A  ences are p r o b a b l y due t o v a r i a t i o n s i n s u r f a c e roughness  .  The  differ-  and hence a r e a .  A  t h e o r e t i c a l v a l u e f o r the o x i d e f i l m t h i c k n e s s , b a s e d on the quantum m e c h a n i c a l " t u n n e l e f f e c t " f o r c o n d u c t i o n o f e l e c t r o n s through the f i l m , t h a t has been der i v e d by  M o t t 3 ^ g i v e s a maximum t h i c k n e s s o f kO A a t room temperature. A l t h o u g h oxide f i l m s formed on aluminum a t room temperature a r e  amorphous, t h o s e formed on molten aluminum are c r y s t a l l i n e ^-AJ-202  25 29 30 38 39 ' ' ' '  - 10 -  FIGURE k. Growth o f o x i d e on aluminum a t o r d i n a r y temperatures 37,  - 11 While some i n v e s t i g a t o r s have f o u n d f i l m s formed a t others  620°C t o he amorphous,  , u s i n g e l e c t r o n d i f f r a c t i o n , have f o u n d c r y s t a l l i n e y - A ^ C ^ i n  }  p r e v i o u s l y amorphous f i l m s a f t e r h e a t i n g f o r one hour a t 500°C o r s i x hours a t ! UOO°C.  The f o r m a t i o n  o f amorphous o r c r y s t a l l i n e f i l m s i s determined b y t h e  r e l a t i v e speeds o f o x i d a t i o n and c r y s t a l l i z a t i o n .  Many i n v e s t i g a t o r s have s t u d i e d a n o d i c a l l y produced oxide f i l m s on aluminum.  These f i l m s f a l l i n t o two c l a s s e s , those formed i n s o l u t i o n s i n  which t h e oxide i s s o l u b l e , and those formed i n s o l u t i o n s i n which i t i s i n s o l uble.  I n the f i r s t  adjacent  case t h e f i l m has a t h i n , c o n s t a n t  thickness, b a r r i e r layer  t o t h e m e t a l and a porous l a y e r which i n c r e a s e s i n t h i c k n e s s w i t h  the v o l t a g e and c u r r e n t d e n s i t y remaining phuric a c i d , phosphoric  constant.  This process, using  time, sul-  a c i d o r chromic a c i d , i s w i d e l y u s e d i n i n d u s t r y t o  form t h i c k , p r o t e c t i v e oxide c o a t i n g s on aluminum.  When anodic f i l m s a r e formed i n an e l e c t r o l y t e which does n o t d i s s o l v e t h e o x i d e , t h e r e s u l t i n g f i l m i s f o u n d t o he amorphous and f r e e from  pores.  At constant voltage the current r a p i d l y f a l l s t o a very small v a l u e , the f i n a l f i l m t h i c k n e s s depending on t h e forming v o l t a g e ^ .  From t h i s Hunter and F o w l e ^ l  have d e v e l o p e d a method f o r measuring t h e t h i c k n e s s o f b a r r i e r f i l m s o r f o r p r o ducing these f i l m s t o a r e q u i r e d t h i c k n e s s .  An e l e c t r o l y t e o f 3$ t a r t a r i c  a c i d , a d j u s t e d t o a pH o f 5.5 w i t h ammonium h y d r o x i d e  a t 24°C, i s u s e d .  In this  s o l u t i o n t h e c u r r e n t d e n s i t y v e r y r a p i d l y f a l l s t o about 10/oA/cnr (see F i g u r e 5) 2  and a f i l m , h a v i n g " t h e f i n a l (leakage)  a t h i c k n e s s o f ik A / a p p l i e d v o l t , i s formed. A l t e r n a t i v e l y c u r r e n t may be determined b y a n o d i z i n g a c l e a n specimen t o  a thickness approximately  e q u a l t o t h a t on a f i l m t o be measured, and t h e n  i n c r e a s i n g t h e v o l t a g e a p p l i e d t o t h e unknown specimen i n t h e e l e c t r o l y t e t h e p r e v i o u s l y determined l e a k a g e c u r r e n t i s r e a c h e d .  until  The f i l m t h i c k n e s s i n  1100  - 12 -  - 13  -  o  Angstrom u n i t s i s then f o u r t e e n times t h e a p p l i e d v o l t a g e .  F o r pure aluminum  the l e a k a g e c u r r e c t v a r i e s o n l y s l i g h t l y over a wide v o l t a g e range, t h i s stage i t was  assumed t h a t t h e f i l m was  v e s t i g a t i o n by Hunter and Towner  c o m p l e t e l y formed.  and a t  Further i n -  has shown t h a t the f i n a l c u r r e n t i s more  t h a n j u s t a l e a k a g e , and t h a t t h e f i l m a c t u a l l y c o n t i n u e s t o grow b y the forma- . t i o n o f porous o x i d e (see F i g u r e 5)p  t h i s would i n d i c a t e t h a t t h e o x i d e i s not  completely i n s o l u b l e i n the e l e c t r o l y t e .  D u r i n g t h e f i r s t twelve minutes o f  •coating time, the b a r r i e r t h i c k n e s s i n c r e a s e s i n i n v e r s e p r o p o r t i o n t o t h e c u r r e n t f l o w , a f t e r which b o t h v a l u e s remain s u b s t a n t i a l l y c o n s t a n t , t h e growth o f the o v e r a l l f i l m t h i c k n e s s c o n t i n u i n g by porous o x i d e f o r m a t i o n . E.  S p e c i f i c Aims o f t h e P r e s e n t I n v e s t i g a t i o n  The  o r i g i n a l aim o f t h i s i n v e s t i g a t i o n was  t o study the wetting  h a v i o u r o f aluminum i n l i q u i d b i s m u t h b y t h e Wilhelmy v e r t i c a l p l a t e  be-  technique  used by Raynor"'"^ i n h i s s i m i l a r i n v e s t i g a t i o n s w i t h t h e t r a n s i t i o n element metals.  I t was  hoped t h a t t h e w e t t i n g b e h a v i o u r would i n d i c a t e t h e mechanism  by which bismuth p e n e t r a t e d t h e aluminum o x i d e f i l m , i f ,  i n f a c t ^ i t was  able  to.  Aluminum was  chosen f o r t h i s study, s i n c e i t was  s o l u b l e i n l i q u i d bismuth t o t h e e x t e n t o f 0.01$ b u t t h a t i t was  a t 300°C and l.k<f> a t  p r o t e c t e d b y an o x i d e f i l m which was  i c a l l y w i t h r e s p e c t t o decomposition,  600°C^,  v e r y s t a b l e thermodynam-  r e d u c t i o n and s o l i d phase r e a c t i o n s w i t h  o t h e r m e t a l s , as mentioned p r e v i o u s l y . by t h e bismuth i t s e l f was  known t h a t i t was  Thus any breakdown o f t h e o x i d e  film  unlikely.  W i t h aluminum i t would a l s o be p o s s i b l e t o a s c e r t a i n the e f f e c t  of  oxide f i l m t h i c k n e s s , s i n c e b y a n o d i z i n g , the f i l m t h i c k n e s s c o u l d be i n c r e a s e d i n an e a s i l y c o n t r o l l e d manner.  - ih -  II.  A..  EXPERIMENTAL - P a r t 1  P r o p e r t i e s o f L i q u i d Bismuth  The bismuth u s e d i n t h e p r e s e n t i n v e s t i g a t i o n was s u p p l i e d i n t h e form o f f o u r pound b a r s b y The C o n s o l i d a t e d M i n i n g and S m e l t i n g Company o f Canada L i m i t e d . ing  The bismuth was o f " i n t e r m e d i a t e g r a d e " and had t h e f o l l o w -  analysis:-  TABLE I A n a l y s i s o f Bismuth  Analysis, parts per m i l l i o n . L o t Ko. Ca [ HPM  3  1+03  -HPM.U52  Cu  0.1  0.1  Al  Fe  Mg  Fb  Si  0.1  -  0.1  0.1  -  -  0.2  0.1  -  0.1  Ag  Wi  2  0.5  0.1  -  The bismuth a l s o c o n t a i n e d a s m a l l q u a n t i t y o f oxygen.  Cd  1.0  However,  m e t a l o f t h i s p u r i t y i s v e r y s a t i s f a c t o r y f o r any experiments i n v o l v i n g  sur-  f a c e t e n s i o n measurements.  S o l i d bismuth has a s i l v e r y appearance.  I t i s e x t r e m e l y b r i t t l e and  thus i s e a s i l y b r o k e n i n t o s m a l l p i e c e s w i t h a hammer. t h i n o x i d e f i l m which i s p r o t e c t i v e i n a i r .  I t i s covered with a  Some o f t h e p h y s i c a l p r o p e r t i e s  o f l i q u i d b i s m u t h a r e l i s t e d i n T a b l e I I , w i t h t h o s e o f sodium and mercury added f o r comparison.  S i n c e t h e d e n s i t y and v i s c o s i t y o f mercury a r e s i m i l a r t o t h o s e o f l i q u i d bismuth, i t may be used f o r t r i a l runs a t room t e m p e r a t u r e .  - 15 TABLE I I  P h y s i c a l P r o p e r t i e s o f L i q u i d Bismuth  Physical  Property  Bismuth  Sodium  Mercury  Melting Point,  °C  271  98  -39  Boiling Point,  °C  1477  883  357  C o n t r a c t i o n on f r e e z i n g  -3^32  2.5  3.6  S p e c i f i c Gravity at melting point, gm/cc  10.6k  0.93  V i s c o s i t y at melting point, centipoises  1.662  0.684  209  Atomic Weight  13.65 1.85 201  23  Pure l i q u i d bismuth i s l i k e mercury i n appearance.  However, i t r e -  a c t s r e a d i l y w i t h t r a c e s o f oxygen and water* vapour t o form t h e b l a c k monoo x i d e , BIO. .The p r e s e n c e o f a d d i t i o n a l oxygen Or water vapour l e a d s t o t h e f o r m a t i o n o f t h e more s t a b l e , y e l l o w leads d i r e c t l y  s e s q u i o x i d e , 6120^.  Excess a i r o r oxygen  t o t h e y e l l o w s e s q u i o x i d e . " A t temperatures g r e a t e r t h a n 600°C,  an orange a l l o t r o p i c  form o f t h e s e s q u i o x i d e e x i s t s .  The s e s q u i o x i d e i s s o l -  u b l e i n l i q u i d bismuth, t h e s o l u b i l i t y i n c r e a s i n g w i t h temperature ( s e e T a b l e I I I ) . I f l i q u i d bismuth i s h e a t e d i n t h e absence o f a i r o r water vapour, i t w i l l  dis-  s o l v e any o x i d e f i l m and p r e s e n t a c l e a n , m e t a l l i c s u r f a c e , p r o v i d e d t h e s u r f a c e area/volume r a t i o , i s s m a l l enough.  TABLE I I I  S o l u b i l i t y ..of .'Bi203 i n " L i q u i d :'Bismuth  Temperature, Solubility, of Oxygen  °C  272  300  400  500  600  12.0  29.O  p.p.m.  0.17  0.34  3.4  - 16 -  N i t r o g e n , hydrogen,  argon and h e l i u m do not r e a c t w i t h , and do not  •kk  d i s s o l v e i n l i q u i d bismuth a protective B.  .  F o r t h i s r e a s o n t h e y are s u i t a b l e f o r use as  atmosphere.  L a b o r a t o r y H a n d l i n g of L i q u i d  Some o f the problems  Bismuth  encountered when h a n d l i n g l i q u i d bismuth i n  the  l a b o r a t o r y are mentioned below.  1)  C o n t a i n e r v e s s e l s f o r l i q u i d bismuth The most c o n v e n i e n t m a t e r i a l f o r h o l d i n g l i q u i d bismuth i s p y r e x  g l a s s , which i s not a t t a c k e d below 500°C=  Above t h i s temperature, however,  bismuth r e a c t s w i t h t h e s o f t e n e d g l a s s t o form a y e l l o w o p a l e s c e n t s u b s t a n c e , which cannot be removed. for  Pyrex g l a s s was  used f o r a l l containment  vessels  l i q u i d bismuth and f o r a l l a n c i l l a r y g l a s s w a r e .  S t a i n l e s s s t e e l s or chrome-vanadium, low a l l o y s t e e l s a r e the o n l y p r a c t i c a l metals f o r h o l d i n g l i q u i d b i s m u t h .  Tantalum, molybdenum, chromium  and b e r y l l i u m are r e p o r t e d t o be s u i t a b l e f o r temperatures up h i g h e r ^ , "but are i m p r a c t i c a l f o r most u s e s .  to 750°C or  P l a t i n u m and n i c k e l - c o n t a i n i n g  a l l o y s d i s s o l v e i n l i q u i d bismuth..  2)  P r o t e c t i v e atmospheres  f o r l i q u i d bismuth  U n l i k e sodium, bismuth w i l l r e a c t w i t h d r y oxygen,  so, not o n l y  must a l l m o i s t u r e be removed from the p r o t e c t i n g gas, b u t a l s o as much oxygen as p o s s i b l e .  Of the p r e v i o u s l y mentioned p r o t e c t i v e gases, the f o l l o w -  i n g were t r i e d : -  a)  helium.  T h i s , however, had t o o h i g h an oxygen c o n t e n t .  A thick  o x i d e f i l m formed on the s u r f a c e o f the l i q u i d bismuth, and c o u l d not be d i s s o l v e d b y r a i s i n g the temperature.  - 17 b)  nitrogen.  T h i s c o n t a i n e d l e s s oxygen t h a n the helium, b u t would not  keep the l i q u i d m e t a l s u r f a c e b r i g h t as l o n g a s - -  c)  n i t r o g e n - h y d r o g e n m i x t u r e s or p l a i n hydrogen, which c o u l d be oxidized with a c a t a l y t i c  Throughout used.  hydrogen  de-  purifier.  the experiments a 3 t o 1 n i t r o g e n - h y d r o g e n m i x t u r e  The n i t r o g e n and hydrogen were f e d from s e p a r a t e c y l i n d e r s ,  was  through  s e p a r a t e f l o w meters, b e f o r e b e i n g mixed and p a s s e d through an E n g e l h a r d "Deoxo" hydrogen p u r i f i e r  t o c o n v e r t any oxygen t o water.  of a p p r o x i m a t e l y f o u r c u b i c f e e t / h o u r was  A t o t a l flow rate  used.  Gas u s e d as a p r o t e c t i v e atmosphere  f o r l i q u i d bismuth must be  he d r i e d extremely w e l l . are  P r e v i o u s experiments ' have show t h a t m o l e c u l a r s i e v e s  s u p e r i o r t o s u l p h u r i c a c i d , anhydrous  c a l c i u m s u l p h a t e or c h l o r i d e ,  s i l i c a g e l , a c t i v a t e d alumina, magnesium p e r c h l o r a t e and phosphorus oxide f o r t h e removal o f water vapour from gasses (see F i g u r e 6 (tlrfion C a r b i d e ) m o l e c u l a r s i e v e s , type 5A, c o n t a i n e d i n U-tube, l o n g , 2.5  cms  pent-  ). 120  "Linde" cms  i n diameter, w i t h g l a s s t a p s a t each end, were u s e d t o remove  m o i s t u r e from a l l gases u s e d i n the experiments. Raynor"^  found i t n e c e s s a r y t o use a l i q u i d bismuth b u b b l e r t o r e -  move oxygen from the argon t h a t he u s e d as a p r o t e c t i v e atmosphere bismuth. i t was  However, u s i n g a n i t r o g e n - h y d r o g e n m i x t u r e , p u r i f i e d  for liquid  as d e s c r i b e d ,  p o s s i b l e t o keep the s u r f a c e o f l i q u i d bismuth c l e a n f o r as l o n g as  d e s i r e d (up t o 5 h o u r s ) .  D e s p i t e the p r e c a u t i o n s r e q u i r e d t o keep a c l e a n s u r f a c e on bismuth, t h e r e appears t o be no f i r e r i s k  s i n c e the o x i d e f i l m ,  once  liquid formed,  - 18 -  I  1  Activated Alumina  -20  J*  Molecular Sieve  -  -p a O ft  >  Q  -6o -80  Silica Gel  L.  5  10  15  20  Wt$ water a d s o r b e d . Dynamic gas d r y i n g .  25  - 19 i s p r o t e c t i v e , and the l i q u i d m e t a l can he s a f e l y poured i n a i r .  For this  r e a s o n i t i s much e a s i e r t o work w i t h t h a n l i q u i d sodium, potassium o r sodiumpotassium  3.  alloy.  F i l t r a t i o n of l i q u i d  bismuth  The o x i d e s o f m e t a l s , p r e s e n t as i m p u r i t i e s i n t h e bismuth, a r e i n s o l u b l e i n t h e l i q u i d m e t a l , though t h e metals themselves may be s l i g h t l y soluble. are  By f i l t e r i n g bismuth a t _the m e l t i n g p o i n t most o f t h e i m p u r i t i e s  removed and t h e oxygen c o n t e n t i s r e d u c e d t o 0.17  p . p . m.  F i l t r a t i o n was c a r r i e d out u s i n g a Pyrex g l a s s f i l t e r  s t i c k , kO cms.  l o n g and 2.5 cms i n diameter, w i t h a s i n t e r e d g l a s s d i s c (EC grade) f u s e d i n t o t h e tube a t i t s lower end, and h a v i n g a gas by-pass tube c a r r y i n g a tap  "A" (see F i g u r e 10).  Lumps o f bismuth were p l a c e d i n t h e f i l t e r Bunsen b u r n e r w h i l e gas p a s s e d down t h e by-pass  tube.  s t i c k and m e l t e d w i t h a The f i l t e r  disc  sup-  p o r t e d t h e m e l t e d bismuth, u n t i l t h e by-pass t a p "A" was c l o s e d and t h e gas p r e s s u r e f o r c e d t h e bismuth t h r o u g h t h e f i l t e r ,  l e a v i n g b e h i n d t h e s o l i d im-  purities .  k)  Assembly  o f apparatus  As i t was i m p o r t a n t t o p r e v e n t c o n t a m i n a t i o n o f t h e bismuth b y g r e a s e , o n l y those ground-glass j o i n t s through which no l i q u i d bismuth were g r e a s e d w i t h s i l i c o n e g r e a s e , a p p l i e d  passed  sparingly.  B e f o r e m e l t i n g t h e bismuth, t h e apparatus was purged w i t h gas t o remove a l l a i r . to  - A l s o t h e system was m a i n t a i n e d a t a s l i g h t p o s i t i v e p r e s s u r e  p r e v e n t i n g r e s s r o f a i r d u r i n g t h e experiment.  - 20 Due t o the expansion o f bismuth on f r e e z i n g , . the l i q u i d m e t a l  was  poured i n t o a s t a i n l e s s s t e e l beaker a t the end o f an experiment t o p r e v e n t breakage o f g l a s s a p p a r a t u s .  A l l g l a s s apparatus was  cleaned with concentrated  n i t r i c a c i d , f o l l o w e d b y r i n s i n g w i t h water and a l c o h o l , and d r y i n g b e f o r e reuse.  C.  D e s c r i p t i o n o f Apparatus  A magnetic b a l a n c e was t h i n aluminum p l a t e as i t was t h e s e measurements i t was  l)  u s e d t o measure the f o r c e s a c t i n g on a  p u l l e d through a l i q u i d bismuth s u r f a c e .  From  p o s s i b l e t o c a l c u l a t e the receding contact angle.  The magnetic b a l a n c e F i g u r e 1 g i v e s a diagrammatic r e p r e s e n t a t i o n o f the magnetic b a l a n c e  assembly.  An  each  side a c o i l  end, p a r a l l e l t o i t s a x i s .  (B) o f a p p r o x i m a t e l y  w i r e , wound oh a Perspex:.former. flat,  i n c h i n d i a m e t e r and 1 l / 2  had rods o f l / l 6 i n c h diameter a u s t e n i t i c s t a i n l e s s  inches long, glued to  " A l n i c o " permanent magnet (A), 3/l6  T h i s was  2000 t u r n s o f  2h  The magnet was  steel  suspended v e r t i c a l l y i n s'.w.g. l a c q u e r e d copper  l o c a t e d l a t e r a l l y by  two  s p i r a l s p r i n g s (c) o f t h i n c o p p e r - b e r y l l i u m a l l o y , which p r o v i d e d v e r y  l i t t l e restraint i n a vertical  direction.  The m e t a l p l a t e s were suspended from the bottom o f t h e magnet a s s embly b y a Pyrex g l a s s f i b r e  (D).  T h i s was  p r e p a r e d by p u l l i n g a p i e c e o f  g l a s s tube t o t h e r e q u i r e d diameter and f u s i n g i n t o each end a s h o r t l e n g t h of tungsten wire (to f a c i l i t a t e  attachment t o b a l a n c e and p l a t e  The combined weight o f the magnet assembly, supported by a stop (E).  clamp).  s u s p e n s i o n f i b r e and p l a t e  was  D  FIGURE 7» Magnetic b a l a n c e assembly.  Scales F u l l  size.  - 22 To measure the f o r c e s a c t i n g on the p l a t e , the t o t a l downward f o r c e was  b a l a n c e d by a n upward f o r c e on the magnet produced by a c u r r e n t  i n the c o i l  (B).  The magnet assembly f l o a t e d o f f . the stop  end touched the f i x e d c o n t a c t block  (G) and was  assembly o f .005  (F).  The  c o n t a c t was  flowing  (E) and i t s upper  mounted i n an i n s u l a t e d  a d j u s t a b l e t o g i v e a t o t a l v e r t i c a l movement o f t h e magnet inches.  The  t h e l i n e t e r m i n a l of the 110  contact  (F) was  connected through a neon b u l b  to  v o l t mains, and the magnet assembly Was grounded,  so t h a t when t h e upward f o r c e j u s t exceeded the downward f o r c e , the neon l i g h t came on.  The  f o r c e was  measured by moving t h e c o a r s e  adjustments (see F i g u r e 8) u n t i l the neon l i g h t  and  the  j u s t came on.  fine The  current  f l o w i n g c o u l d be determined by measuring the v o l t a g e drop a c r o s s a 0.1  ohm  r e s i s t o r with a T i n s l e y Portable Potentiometer.  standard  The b a l a n c e  was  c a l i b r a t e d by hanging weights on i t and n o t i n g the v o l t a g e drop a t t h e ancing c u r r e n t . the b a l a n c e was  The  The + 20  c a l i b r a t i o n curve i s shown i n F i g u r e 9°  accuracy  of  mg.  complete b a l a n c e  was  f i x e d t o a b r a s s nut  t i c a l l y on the screw r o d (K) o f t e n threads the k n u r l e d d i s c (L) moved-the b a l a n c e  The  inches.  The  turn of disc  complete assembly was  had clamped  By l o o s e n i n g t h i s clamp, t h e assembly c o u l d v be moved v e r t i c a l l y through a range o f two f e e t .  2)  a v e r t i c a l aluminum  (H) which moved v e r -  per i n c h , so t h a t one  v e r t i c a l l y 0.1  a c l i c k stop o p e r a t i n g once per r e v o l u t i o n . to  The  bal-  The  "T" beam.  g l a s s apparatus The whole of the apparatus was  It  made o f Pyrex g l a s s (see F i g u r e  c o n s i s t e d o f t h e main c o n t a i n e r , 2 l/2 i n c h e s i n diameter and 8 l/2  t a l l , w i t h two  upswept side-arms and a two-piece v e r t i c a l e x t e n s i o n ^  10).  inches  down  - 23 12 V o l t s  -vww18  Ohms  Coarse Adjustment  AAAM/WvWvVV  1  22 Ohms Fine Adjustment  18 Ohms  0-500 Ohms.  Ammeter ,0-1 Amps.  Magnetic Balance. 8 Ohms  Standard Resistor  A / W  0.1  Ohms.  Tinsley Portable Potentiometer  FIGURE 8 . Magnetic b a l a n c e c i r c u i t  diagram.  Gas  (—1  A  Filter Stick  t<\  Inlet  Suspension Fibre  - 26 which the s u s p e n s i o n f i b r e p a s s e d .  One  side-arm c a r r i e d the f i l t e r  p r e v i o u s l y d e s c r i b e d , c a p a b l e o f h o l d i n g 850  grams o f b i s m u t h .  stick,  The o t h e r  p r o v i d e d access f o r a g l a s s sheathed chromel-alumel thermocouple,  which  dipped i n t o the l i q u i d bismuth.  The l i q u i d bismuth was was  c o n t a i n e d i n t h e Pyrex g l a s s v e s s e l ,  p r o t e c t e d from o x i d a t i o n b y a m i x t u r e o f n i t r o g e n and hydrogen,  and  which  e n t e r e d t h r o u g h the f i l t e r s t i c k and p a s s e d out through the v e r t i c a l e x t e n sion.  T h i s e x t e n s i o n was reduced i n diameter towards the top t o t h e s m a l l e s t  diameter t h a t would a l l o w f r e e passage o f the s u s p e n s i o n f i b r e .  3.  H e a t i n g and temperature  control.  The bottom s e c t i o n o f the g l a s s v e s s e l c o n t a i n i n g t h e l i q u i d b i s m u t h was h e a t e d by a 200 watt T h i s mantle was  " E l e c t r o t h e r m a l " h e a t i n g mantle  (Type MJ 1504  connected t o t h e power s u p p l y through a "Wheelco" Model  EX  6).  402  i n d i c a t i n g c o n t r o l l e r , which a l s o accommodated t h e thermocouple.  The Model 402  c o n t r o l l e r i s an o f f - o n or t w o - p o s i t i o n temperature  c o n t r o l l e r w i t h an a d j u s t a b l e t i m e - p r o p o r t i o n i n g d e v i c e t o minimize v a r i a t i o n at the c o n t r o l set p o i n t .  control  The c o n t r o l a c t i o n o c c u r s when t h e meter  i n d i c a t o r i s at the r e d c o n t r o l set p o i n t e r .  The i n s t r u m e n t has a range o f 0 t o 800°C and d u r i n g the experiments the  temperature v a r i e d no more t h a n 2°C e i t h e r s i d e o f the s e t temperature.  he  Preparation of plates (  " S u p e r p u r i t y " aluminum ( 9 9 - 9 8 $ 0 and A l c a n 2S a l l o y were u s e d i n t h e experiments.  The a n a l y s e s o f t h e s e m a t e r i a l a r e g i v e i n T a b l e IV»  - 27 TABLE IV A n a l y s e s o f Aluminum  Analysis i n percent  Material Cu 'Superpurity' A l c a n 2S  Fe  .005 .02  .52  Balance  The  Si  .Mg  Trace  .008  .Ik  .010  Mn  Ti  -  Trace  .05  <,010  Zn  Cr  -  -  Wi  V  .008  .01  <.010 <.010  - Aluminum  a l l o y specimens were c u t from l 6 gauge (1.5  mm) A l c a n 2S  "Utility"  sheet, which had been r o l l e d down t o O.h mm.  The  " s u p e r p u r i t y " aluminum was a v a i l a b l e i n i n g o t form.  A slab,  a p p r o x i m a t e l y 6 cms b y 2.5 cms b y 1 cm, was c u t from t h e c e n t r e o f an i n g o t s e c t i o n and was r o l l e d down t o a p p r o x i m a t e l y 0.0k cms t h i c k , w i t h one i n t e r mediate a n n e a l i n a i r a t 500°C f o r one hour.  The p l a t e s were c u t t o s i z e from t h e 0.0k cms sheet w i t h a g u i l l o t i n e , and t h e edges rounded b y p o l i s h i n g w i t h emery.  The by 1.2  cms b y 0.0k cms.  the w e t t i n g  a)  o f t h e aluminum p l a t e s used were a p p r o x i m a t e l y 3-2 cms  dimensions  Two d i f f e r e n t s u r f a c e p r e p a r a t i o n s were used f o r  experiments:-  M e c h a n i c a l p o l i s h i n g under kerosene w i t h 0, 2/0 and 3/0 emery paper, f o l l o w e d by degreasing i n chlorethane.  b)  as ( a ) , b u t f o l l o w e d b y e l e c t r o p o l i s h i n g f o r 2 minutes a t 2k v o l t s i n a s o l u t i o n o f 15$ p e r c h l o r i c a c i d i n a c e t i c a c i d . were t h e n washed i n water and a l c o h o l .  The p l a t e s  - 28 All  specimens  u n t i l ready f o r use. plate'were noted.  were kept i n a d e s s i c a t o r c o n t a i n i n g m o l e c u l a r  B e f o r e each experiment, the dimensions  The p l a t e was  o f a clamp (see F i g u r e  11)  and weight  sieves o f each  t h e n a t t a c h e d t o the s u s p e n s i o n w i r e by means  so t h a t i t hung  vertically.  •Suspension Wire  -Weight  0  P l a t e Clamp  -Plate  FIGURE 1 1 .  Plate  attachment.  The h i g h d e n s i t y o f l i q u i d bismuth p r e s e n t e d a problem. t r i a l runs t h e aluminum p l a t e tended t o f l o a t  and d r i f t e d  t o the s i d e o f t h e  v e s s e l , d e s p i t e the c o m p a r i t i v e r i g i d i t y o f the Pyrex f i b r e ever, i t was  f o u n d t h a t , i f a b r a s s weight was  the  aluminum p l a t e would hang  D.  E x p e r i m e n t a l Procedure  The apparatus was  During  suspension.  added above the p l a t e  How-  clamp,  vertically.  f l u s h e d out w i t h N 2 - H 2 m i x t u r e f o r 1 1 / 2  hours and the l i q u i d bismuth v e s s e l was  p r e h e a t e d t o about 300°C.  to 2 The  - 29 bismuth, i n t h e f i l t e r  s t i c k was m e l t e d w i t h a Bunsen b u r n e r and f i l t e r e d b y  c l o s i n g t h e t a p i n t h e s i d e arm. depth o f about 5  c m s  •  The l i q u i d bismuth f i l l e d t h e v e s s e l t o a  I t was h e a t e d t o 500°C t o d i s s o l v e any s u r f a c e o x i d e  b e f o r e a d j u s t i n g t h e temperature t o t h e d e s i r e d  level.  With t h e nut ( H ) ( s e e F i g u r e 7 ) one t u r n below t h e t o p o f i t s t r a v e l , t h e whole magnetic b a l a n c e assembly was lowered on t h e "T" beam u n t i l the  bottom  o f t h e p l a t e j u s t touched t h e s u r f a c e o f t h e l i q u i d b i s m u t h .  was t h e n clamped  t o t h e beam.  The p l a t e ( p l u s t h e magnetic b a l a n c e ) was t h e n  lowered one i n c h by t u r n i n g t h e d i s c started.  ( L ) t h r o u g h t e n t u r n s , and t h e t i m i n g was  A s c a l e ( M ) a l o n g s i d e t h e r a i s i n g and l o w e r i n g screw i n d i c a t e d t h e  p o s i t i o n o f t h e plate,, at  It  A f t e r one minute  a time (one t u r n o f t h e d i s c  t h e p l a t e was withdrawn 0.1  inches  ( L ) as i n d i c a t e d b y t h e c l i c k - s t o p ) , t h e  force  on t h e p l a t e was b a l a n c e d a t each s t o p and t h e p o t e n t i o m e t e r r e a d i n g n o t e d . When t h e p l a t e was c l e a r o f t h e l i q u i d ,  an " o u t - r e a d i n g " was t a k e n t o i n d i c a t e  any l o s s o r g a i n i n t h e weight o f t h e p l a t e .  The p l a t e was immediately r e -  immersed and t h e above p r o c e d u r e r e p e a t e d e v e r y t e n m i n u t e s .  One s e t o f  r e a d i n g s , from t h e s t a r t o f r a i s i n g t o reimmersion i n t h e bismuth, took from t h r e e t o f o u r minutes  depending on how much adjustment  p o t e n t i o m e t e r was needed.  The f a c t t h a t t h e bottom  o f t h e b a l a n c e and  o f t h e p l a t e was im-  mersed f o r l o n g e r t h a n t h e t o p was accounted f o r i n c a l c u l a t i n g t h e r e s u l t s .  E.  Theory The f o r c e s a c t i n g on t h e p l a t e a r e r e p r e s e n t e d i n F i g u r e 12 and  are: a)  The upward f o r c e , F grams, due t o t h e t e n s i o n i n t h e s u s p e n s i o n w i r e . T h i s i s a l s o t h e f o r c e r e c o r d e d b y t h e magnetic b a l a n c e .  - 30 -  Surface tension force.  FIGURE 12. F o r c e s on the p l a t e i n l i q u i d b i s m u t h .  b)  t h e v e r t i c a l component o f t h e s u r f a c e t e n s i o n ^ a c t i n g a t a c o n t a c t a n g l e o f 9 t o the p l a t e , g i v i n g a v a l u e o f y c o s 9 dynes/cm.  c)  t h e n e t weight Wgms = t o t a l weight-bouyancy  force  The t o t a l weight i n c l u d e s t h e weight o f t h e p l a t e , clamp, and s u s pension f i b r e .  .  The bouyancy f o r c e = t(w) (x) ( p ) . where t = t h i c k n e s s o f p L a t e i n cms. w = w i d t h o f p l a t e i n cms. x = l e n g t h o f p l a t e immersed i n bismuth i n cms. jo = d e n s i t y o f l i q u i d b i s m u t h . (The v a l u e u s e d was t h a t o f Bircumshaw the  hi  i  and was 10.03 gms/cc a t t h e m e l t i n g p o i n t ,  temperature c o e f f i c i e n t  b e i n g -0.00.3 g m s / c c / ° C ) .  - 31 R e s o l v i n g v e r t i c a l l y , we have; 2 ( t + w) g  ycos 6 = F - W  From t h e above e q u a t i o n and Raynor's" "^ v a l u e o f t h e s u r f a c e t e n s i o n 1  o f l i q u i d , bismuth, t h e c o n t a c t angle 9 c a n be c a l c u l a t e d .  Accuracy of r e s u l t s  The a c c u r a c y t o which t h e c o n t a c t angle c o u l d be determined depended on a number o f f a c t o r s ; - t h e approximate a)  t h i c k n e s s and w i d t h o f p l a t e  b)  n e t weight o f p l a t e  c)  surface tension.  e r r o r f o r each i s g i v e n below:-  +0.2$ +1.0$  The v a l u e used h a d an a c c u r a c y o f + 1.0$.  v a r i a t i o n o f temperature would produce a change o f o n l y d)  Any  +0.01$  p e r °C.  t h e magnetic b a l a n c e r e a d i n g had an a c c u r a c y o f + 20 mg throughout the range, g i v i n g much lower percentage a c c u r a c y a t low r e a d i n g s , i . e . when t h e c o n t a c t a n g l e was g r e a t e r t h a n 90°.  The a c c u r a c y  v a r i e d between 2$ and 0.5$.  The n e t e r r o r may be up t o 7$; b u t would be lower t h a n t h i s f o r cont a c t a n g l e s near 0°,  as t h e p e r c e n t a g e e r r o r i n t h e magnetic b a l a n c e r e a d i n g  i s a minimum a t t h i s  point.  F.  Analysis of Results  B e f o r e p r o c e e d i n g i t i s n e c e s s a r y t o d e f i n e t h e d i f f e r e n t degrees o f w e t t i n g t h a t a r e used i n t h e d i s c u s s i o n o f r e s u l t s .  D e f i n i t i o n of wetting a)  W e t t i n g and p a r t i a l w e t t i n g w i l l i m p l y c o n t a c t a n g l e s l e s s t h a n  9°°.  - 32 b)  Complete w e t t i n g w i l l imply a c o n t a c t a n g l e o f zero and i s r e c o g n i z e d by t h e presence o f l i q u i d m e t a l a d h e r i n g t o the s o l i d Non-wetting w i l l i m p l y a c o n t a c t a n g l e g r e a t e r t h a n 90°  c)  metal.  and i s  r e c o g n i z e d by the absence o f l i q u i d m e t a l a d h e r i n g t o the  solid  metal. o C o n t a c t angles were measured a t v a r i o u s temperatures and 500°C f o r m e c h a n i c a l l y p o l i s h e d A l c a n 2S polished a n g l e was  " s u p e r p u r i t y " aluminum. examined a t each  between 350  and m e c h a n i c a l l y and  C  electro-  The i n f l u e n c e o f immersion time on c o n t a c t  temperature.  The r e s u l t s were c a l c u l a t e d u s i n g the e q u a t i o n g i v e n i n S e c t i o n E . T a b l e V shows a t y p i c a l c a l c u l a t i o n o f the c o n t a c t a n g l e .  The p o s i t i o n column  g i v e s t h e r e a d i n g o f the v e r t i c a l p o s i t i o n s c a l e (M i n F i g u r e 7)  and  indicates  the depth o f immersion o f the aluminum p l a t e i n t h e l i q u i d bismuth i n u n i t s of  0.1  inches.  The f i r s t  t h r e e columns are those r e c o r d e d d u r i n g the e x p e r i -  ment.  The c o n t a c t a n g l e v e r s u s time r e l a t i o n s h i p was  plotted either  as  a group o f curves each r e p r e s e n t i n g a d i f f e r e n t p o s i t i o n on the p l a t e , o r as a curve r e p r e s e n t i n g t h e average  F i g u r e 13  c o n t a c t a n g l e over the whole p l a t e .  shows a p l o t o f the f i r s t  type.  Each c u r v e shows the  change o f c o n t a c t angle w i t h time a t a p a r t i c u l a r l e v e l on the p l a t e ( o n l y f o u r a r e shown f o r c l a r i t y ) , and each p o i n t r e p r e s e n t s t h e average angle a t t h i s l e v e l . pattern.  contact  I t w i l l be observed t h a t the curves f o l l o w the same  - 33 TABLE V  Sample C a l c u l a t i o n o f C o n t a c t Angle  P l a t e 5 M e c h a n i c a l l y p o l i s h e d A l c a n 2S Time P o s i t i o n mins.  1.00  4.00  y= 362.0  Potentiometer Reading M V  F gms  9  39-65  8  500°C Cos 0  e  gms  S gms  1.162  1.978  -.816  -.969  40.15  1.279  2.088  -.809  -.96O 164.  1.37  7  41.03  1.486  2.201  -.715  -,8k$  148.  1.75  6  4l.4o  1.572  2.311  -.739  -.877  151.5  2.12  5  41.85  1.678  2.423  -.7-45  -.884  152.  2.50  4  42.19  1.758  2-533  -•775  -.920  157.  2.87  3  42.97  1.941  2.645  -.704  -.836  146.5  3.25  2  •^3-79  2.133  2-757  -.624  -.741  138.  3.62  l  M+-53  2.307  2.868  -.561  -.666  131.5  4.00  165.5  Immersion Time-mins.  1.00  dynes/cm;  p =  9°73  gms/cc.  w =>  1.101  cms.  t = 0.0409 cms. ' P o s i t i o n ' i s t h e r e a d i n g o f t h e p o i n t e r on t h e b a l a n c e and r e p r e s e n t s t h e l e n g t h o f p l a t e immersed i n u n i t s o f 0.1 S = F - W = y c o s 0 .2(w  inches.  + t) g  F = Magnetic b a l a n c e r e a d i n g W = Wet weight .= T o t a l weight - Bouyancy f o r c e  Immersion Time, minutes.  - 35 Curves  o f the second t y p e are shown i n F i g u r e s 14 and 15".  The  c o n t a c t a n g l e p l o t t e d i n t h i s case i s the average over a l l p o s i t i o n s  for  one w i t h d r a w l o f t h e p l a t e .  T h i s curve w i l l r u n t h r o u g h the c e n t r e o f the  group o f c o r r e s p o n d i n g curves o f t h e f i r s t t y p e . (Compare the p l o t s f o r p l a t e l 4 i n F i g u r e s 13  F i g u r e 14 e r a t u r e s o f 400,  450  and  15)  shows the v a r i a t i o n o f c o n t a c t a n g l e w i t h time a t tempand 500°C f o r p l a t e s o f m e c h a n i c a l l y p o l i s h e d A l e a n  2S.  I t w i l l he seen t h a t the I n i t i a l c o n t a c t a n g l e i s t h e same i n each ease h u t t h a t i t decreases f a s t e r w i t h immersion time a t t h e h i g h e r t e m p e r a t u r e s .  The w e t t i n g b e h a v i o u r o f m e c h a n i c a l l y p o l i s h e d " s u p e r p u r i t y " aluminum a t temperatures  of  350> 400,  450 and  500°C i s shown i n F i g u r e 15.  The i n i t i a l i n c r e a s e i n the c o n t a c t a n g l e i n t h e case o f the two lower tempe r a t u r e curves was  p r o b a b l y due t o a s l i g h t i n c r e a s e i n t h e f i l m t h i c k n e s s  caused b y a p i c k - u p by t h e aluminum o f oxygen d i s s o l v e d i n t h e bismuth.  A s i m i l a r e f f e c t was  and vanadium.  o b s e r v e d b y R a y n o r ^ on niobium,  liquid tantalum  The I n i t i a l i n c r e a s e i n t h e c u r v e a t 450°C i s p r o b a b l y due  t o t h e same cause.  The  maxima  o f t h e s e curves tended t o s h o r t e r t i m e s and t h e  slope i n c r e a s e d uniformly with i n c r e a s i n g  The c u r v e s i n F i g u r e s l 4  and 15  i n c o n t a c t a n g l e w i t h immersion t i m e .  temperature.  appear t o show a s t e a d y d e c r e a s e  However, the c o n t a c t a n g l e shown I s 13,  a c t u a l l y t h e average a n g l e over t h e whole p l a t e , o r , i n the case o f F i g u r e over each l e v e l on the p l a t e .  V i s u a l o b s e r v a t i o n o f t h e p l a t e s (see F i g u r e  showed t h a t a t any l e y e l on t h e p l a t e , c o n d i t i o n s would v a r y from complete ting, to  non-wetting.  16)  wet-  - 37 -  o  FIGURE 1$.  J  1  ko  Wetting behaviour of mechanically p o l i s h e d 99.98$ aluminum.  0 500°C  Plate  15.  A 450°C  "  8.  o Loo°C  "  6.  • 350°C  "  14.  1  60  Immersion Time, minutes.  1  80  i _  100  8  9  Figure  l6  (b)  M e c h a n i c a l l y p o l i s h e d 99-98$ aluminum a f t e r exposure t o l i q u i d b i s m u t h a t v a r i o u s temperatures and times l i s t e d below. a)  b)  P l a t e lk " 18 6 Plate 9  350°C kOO°Q kOO°C H-50°C  8  450°C  123 minutes 76 YLk 23  3k  - 39 At f i r s t  s t a i n e d areas woiild appear,  f o l l o w e d b y areas with, bismuth  adhering  and .areas showing a t t a c k , o f t e n edge a t t a c k ; a l l these--areas w o u l d be c o m p l e t e l y wet by t h e l i q u i d bismuth.  The s t e a d y decrease i n c o n t a c t a n g l e shown i n  F i g u r e s . Ik and 15, t h e r e f o r e , r e p r e s e n t s n o t a g e n e r a l d e c r e a s e , h u t a s p r e a d ing  o f areas on t h e p l a t e t h a t a r e c o m p l e t e l y w e t t e d .  A t .the lower  .actual a t t a c k was u s u a l l y l i m i t e d t o t h e edge o f t h e p l a t e  temperatures,  ( F i g u r e 16, a and b ) .  W i t h i n c r e a s e d temperature more severe a t t a c k o c c u r r e d w i t h c o n s i d e r a b l e s o l u t i o n o f t h e aluminum ( F i g u r e l 6 ( b ) ) a l t h o u g h some areas p f t h e p l a t e were not  wetted.  A f t e r s o l u t i o n o f one t e n t h o r more o f t h e aluminum p l a t e i n t h e bismuth, bismuth  t h e c o n t a c t a n g l e measurements h a d t o be stopped,  since the l i q u i d  s u r f a c e became c o v e r e d w i t h an aluminum o x i d e l a y e r , even though I t  c o n t a i n e d no more t h a n 10 p . p . m. o f d i s s o l v e d aluminum. was a l s o s u f f i c i e n t  This concentration  t o prevent the formation of i n t e r f e r e n c e colours i n the  o x i d e f i l m when t h e l i q u i d bismuth was poured i n a i r a t t h e end o f t h e experiment.  Three p l a t e s t h a t h a d "been e l e c t r o p o l i s h e d as d e s c r i b e d e a r l i e r , were t e s t e d and a l l were f o u n d t o wet c o m p l e t e l y and u n i f o r m l y , w i t h .uniform s o l u t i o n and t h i n n i n g o f t h e p l a t e .  S i n c e c o n t a c t a n g l e measurements c o u l d g i v e no more t h a n t h e r a t e o f i n c r e a s e o f w e t t e d a r e a s , i t was d e c i d e d t o abandon t h i s  experimental  t e c h n i q u e and develop a procedure whereby a c o r r e l a t i o n c o u l d be a c h i e v e d between t h e time a t which t h e aluminum p l a t e was f i r s t bismuth  and t h e s u r f a c e c o n d i t i o n o f t h e aluminum oxide  attacked by the l i q u i d film.  - i+o III.  A.  EXPERIMENTAL - P a r t 2  D e s c r i p t i o n o f Apparatus  The  same apparatus was  'the magnetic b a l a n c e , which was  u s e d as i n p a r t 1, w i t h t h e e x c e p t i o n r e p l a c e d by a l / l 6 i n c h diameter  of  stainless (  s t e e l r o d clamped d i r e c t l y t o the nut H ( F i g u r e 7) p l a t e clamp s i l v e r s o l d e r e d t o the bottom l)  a t the top and w i t h  the  end.  Preparation of plates The  used b e f o r e . surface  a)  aluminum p l a t e s were o f the same s i z e and m a t e r i a l as The  " s u p e r p u r i t y " aluminum p l a t e s were g i v e n the f o l l o w i n g  treatments:-  M e c h a n i c a l p o l i s h i n g under kerosene on 0, f o l l o w e d by d e g r e a s i n g  b)  those  in  2/0  and 3/0  emery paper  chlorethane.  C l e a n i n g by immersion f o r f i v e minutes i n a s o l u t i o n o f 35 phosphoric  a c i d (85$)  and 20 g m s / l i t r e chromium oxide a t 100°C  and f o r f i v e minutes i n a 50 80°C.  ml/litre  g m / l i t r e sodium .carbonate s o l u t i o n a t  They were t h e n a n o d i z e d  i n a 3$ ammonium t a r t r a t e s o l u t i o n 41  as d e s c r i b e d by Hunter and Fowle  .  The  f o l l o w i n g v o l t a g e s were  used:1Q v o l t s g i v i n g an approximate f i l m t h i c k n e s s of 140  o A 0  15 "volts" g i v i n g an approximate f i l m t h i c k n e s s of* 210  c)  A  o 20 v o l t s g i v i n g an approximate f i l m t h i c k n e s s o f 280 A . o 30 v o l t s g i v i n g an approximate f i l m t h i c k n e s s o f 420 A C l e a n i n g as i n (b) and a n o d i z i n g i n 15$ s u l p h u r i c a c i d a t 15 v o l t s and 20°C t o g i v e a porous oxide f i l m a p p r o x i m a t e l y  14 microns  51 thick  .  One  such f i l m was  f o r 30 m i n u t e s .  s e a l e d by immersion i n b o i l i n g water  ~ kl -  B.  Experimental Procedure  The apparatus was f l u s h e d out w i t h f i l t e r e d as d e s c r i b e d i n p a r t 1.  N2-H2 m i x t u r e and t h e bismuth  The aluminum p l a t e , clamped  t o t h e bottom  end o f the s t a i n l e s s s t e e l r o d , was l o w e r e d u n t i l i t j u s t t o u c h e d t h e l i q u i d bismuth s u r f a c e , and t h e r a i s i n g and l o w e r i n g mechanism was clamped t o t h e "T" beam.  The p l a t e was t h e n immersed i n t h e l i q u i d bismuth t o a depth o f  1 i n c h by means o f t h e screw mechanism (K i n F i g u r e 7.) •  At  t h e end o f t h e f i r s t minute  t h e p l a t e was q u i c k l y withdrawn  from t h e l i q u i d bismuth f o r e x a m i n a t i o n and immediately reimmersed. was r e p e a t e d a t t h e end o f t h e f i r s t for  f i v e minutes  and e v e r y f i v e  This  minutes  t h e f i r s t hour, and t h e n e v e r y t e n minutes u n t i l t h e p l a t e was a t t a c k e d .  As t h e p l a t e was withdrawn, i t s s u r f a c e was c a r e f u l l y examined f o r s t a i n i n g , a d h e r i n g bismuth, p i t t i n g or any o t h e r forms o f a t t a c k which were n o t e d t o g e t h e r - w i t h t h e time a t which  All i n Appendix of  t h e p l a t e s t e s t e d b y immersion i n l i q u i d b i s m u t h a r e l i s t e d  I , t o g e t h e r w i t h d e t a i l s o f t h e t e s t i n g c o n d i t i o n s and t h e type  attack that occurred.  immersion  they occurred.  I n t h e column headed "Time" i s g i v e n t h e time o f  a t which a t t a c k b y t h e l i q u i d bismuth was b e l i e v e d t o have  started.  T h i s time was e x t r e m e l y d i f f i c u l t t o e s t i m a t e as many o f t h e p l a t e s had b i s muth a d h e r i n g t o t h e s u r f a c e i n s m a l l d r o p s . concentrated n i t r i c  I f t h e p l a t e was immersed i n  a c i d a f t e r t h e t e s t , any bismuth on t h e p l a t e was r a p i d l y  d i s s o l v e d and i n many cases i t was f o u n d t h a t t h e aluminum p l a t e was p i t t e d where t h e bismuth had been l o c a t e d .  I t was i m p o s s i b l e t o t e l l whether t h e  bismuth adhered t o t h e p l a t e because  t h e f i l m had a l r e a d y been p e n e t r a t e d o r  whether p e n e t r a t i o n o c c u r r e d a f t e r t h e bismuth adhered t o t h e p l a t e and had established close contact with the f i l m . former i s t h e c a s e .  I t i s b e l i e v e d , however, t h a t t h e  - k2 -  C.  A n a l y s i s of Results  I n g e n e r a l , the aluminum p l a t e s were attacked, i n one or i n some cases  a combination o f the two.  I n one  o f two  case the p l a t e s  first  became s t a i n e d , p a r t i c u l a r l y  round the edges; t h i s was  adhering  edges o f the p l a t e s i n s m a l l drops (see  l6).  The  t o the s u r f a c e s and first visible  s i g n s o f a t t a c k were one  the edges o f the p l a t e s .  I n some cases  be removed w i t h a f i n g e r n a i l ,  although,  p i t s were f o u n d when the bismuth was num  bismuth Figure  or more s m a l l notches  the adherent bismuth c o u l d  In  easily  as mentioned p r e v i o u s l y , i n o t h e r s ,  dissolved.  d i s s o l v e d i n the l i q u i d bismuth was  f o l l o w e d by  ways,  The  r a t e a t which the  slow and t h e r e was  alumi-  o n l y a s m a l l number  o f p o i n t s o f a t t a c k , o f t e n not more t h a n t h r e e or f o u r .  I n the second type num  o f a t t a c k , t h e bismuth, on p e n e t r a t i n g the  oxide f i l m , would r a p i d l y s p r e a d under the f i l m .  i n the f i l m ,  i n d u c e d by t h e oxide/metal  caused the oxide f i l m t o w r i n k l e .  The  alumi-  compressive s t r e s s e s  volume r a t i o b e i n g g r e a t e r t h a n  On withdrawing the p l a t e from the  one,  liquid  bismuth, the bismuth t r a p p e d under the oxide f i l m would r u n t o the bottom of the p l a t e and form a b u l g e i n the f i l m  (see F i g u r e  17)-  When a p l a t e t h a t had been a t t a c k e d i n the l a t t e r way a l a y e r o f bismuth c o u l d be F i g u r e 18 has  seen between the aluminum and t h e oxide  shows a v e r t i c a l s e c t i o n o f the bottom o f p l a t e 19  c o l l e c t e d i n a b u l g e under the o x i d e  The m e c h a n i c a l l y  was  sectioned, film.  where t h e bismuth  film.  p o l i s h e d specimens g e n e r a l l y showed a  c o n s i s t e n t form o f a t t a c k i n the l i q u i d b i s m u t h .  fairly  - k3 -  15  FIGURE  17.  18.  2  0  M e c h a n i c a l l y p o l i s h e d 99.98$ A l a f t e r immersion i n l i q u i d bismuth at the f o l l o w i n g temperatures. a) P l a t e 15 500°C f o r Ik m i n u t e s .  b) c)  FIGURE  19  "  19 20  500°C f o r 15 minutes. 500°C f o r 10 minutes.  A v e r t i c a l s e c t i o n o f p l a t e 19, m e c h a n i c a l l y p o l i s h e d 99.98$ A l a f t e r immersion I n l i q u i d bismuth f o r 15 minutes a t 500°C. showing bismuth under t h e o x i d e f i l m a t t h e b o t t o m o f t h e p l a t e . Magnification 11OX.  - kh The A l c a n 2S specimens showed t h e f i r s t  type o f a t t a c k i n a l l cases  S t a i n i n g o f t h e p l a t e was f o l l o w e d b y b i s m u t h a d h e r i n g f i n a l l y b y edge a t t a c k .  to the  surface,  and  On d i s s o l v i n g o f f t h e bismuth, i t was f o u n d t h a t  most p l a t e s were p i t t e d underneath.  I n t h e case o f two p l a t e s t h a t were  s e c t i o n e d , i n t e r g r a n u l a r a t t a c k was a l s o v i s i b l e I n t h e aluminum around t h e pits  (see F i g u r e  F i g u r e 19  19).  S e c t i o n o f p l a t e 33, m e c h a n i c a l l y p o l i s h e d A l c a n 2S, a f t e r immers i o n i n l i q u i d b i s m u t h f o r 15 minutes a t ^00°C showing p i t t i n g and i n t e r g r a n u l a r a t t a c k . M a g n i f i c a t i o n 99QX. f  The  A l c a n 2S p l a t e s were a t t a c k e d more q u i c k l y a t t h e h i g h e r  e r a t u r e s , b u t t h e r e was c o n s i d e r a b l e  s c a t t e r i n the values  temp-  o f the* time t a k e n  t o i n i t i a t e a t t a c k , which cannot be e n t i r e l y a c c o u n t e d f o r b y t h e u n c e r t a i n t y I n t h e p r e c i s e moment a t which t h e a t t a c k  commenced.  The  " s u p e r p u r i t y " aluminum p l a t e s were a t t a c k e d I n the same  as the a l l o y specimens a t 35°  way  and 400°C, h u t w i t h l e s s p i t t i n g on t h e  surface  o f the p l a t e , and no s i g n o f i n t e r g r a n u l a r a t t a c k (see F i g u r e l 6 a ) . ,450°C, the s t a i n i n g was  45 -  At  f o l l o w e d "by p e n e t r a t i o n o f the f i l m a t a number o f  p l a c e s and non-uniform a t t a c k on the aluminum'under the f i l m (see F i g u r e 16  b).  o A t 500  C the second t y p e of a t t a c k predominated w i t h r a p i d s p r e a d i n g  o f the 17)«  bismuth under the oxide f i l m and f a i r l y severe l o c a l a t t a c k . ( s e e F i g u r e A g a i n t h e r e was to  the wide s c a t t e r i n the v a l u e s o f the time t a k e n f o r a t t a c k  start. The r e s u l t s f o r the 99-98$ 'aluminum, a n o d i z e d  solution,'showed  i n ammonium t a r t r a t e  even l e s s r e p r o d u c a b i l i t y t h a n p r e v i o u s r e s u l t s . o  though the minimum f i l m t h i c k n e s s u s e d was f o r the m e c h a n i c a l l y  o  A compared w i t h 20-40 A  p o l i s h e d specimens, no s i g n i f i c a n t i n c r e a s e i n the r e -  s i s t a n c e t o a t t a c k was The  140  Even  produced, except f o r the t h i c k e r f i l m s (280  second type o f a t t a c k , i n v o l v i n g complete removal o f the oxide  and 420  A).  film  f o l l o w e d by r a p i d s o l u t i o n o f the aluminum, o c c u r r e d more f r e q u e n t l y i n t h e s e t e s t s and was  not c o n f i n e d t o the h i g h e r temperatures.  The  oxide f i l m .often  f l o a t e d o f f the p l a t e i n b u l k and l a y on the s u r f a c e of the b i s m u t h on e i t h e r s i d e o f the p l a t e i n l a r g e p i e c e s . the a t t a c k was  v e r y l o c a l i z e d , o f t e n appearing  points, with l i t t l e show the types  However, when the f i l m was  F o u r specimens were anodized - thickness of approximately  l4  on a n o d i z e d i n 15$  microns-'-'".  One  detached,  t o spread from o n l y one  s t a i n i n g or adherent b i s m u t h elsewhere.  of attack t h a t ocpurred  not  or  two  F i g u r e s 20 and  21  specimens..  sulphuric a c i d to give a f i l m p l a t e t e s t e d at 400°C and  a t 500°C showed no a t t a c k a f t e r 3 and 5 hours r e s p e c t i v e l y .  one  Another p l a t e  was  - he -  FIGURE 21. P l a t e s 25, 21, and 12 (lj+O % a n o d i z e d f i l m ) af£er immersion i n l i q u i d "bismuth a t 50t C f o r 25 minutes, 450 C f o r 9 minutes and 42 minutes r e s p e c t i v e l y .  - kl -  h e l d j u s t above t h e l i q u i d bismuth s u r f a c e a t before  e n t e r i n g the h o t l i q u i d .  t r a v e l l i n g up t h e p l a t e . had  t o a l l o w i t t o heat up  As i t was l o w e r e d i n t o t h e l i q u i d  the aluminum o x i d e f i l m f l o a t e d o f f t h e p l a t e . b e f o r e i t was c o m p l e t e l y  500°C  metal,  The p l a t e was withdrawn  immersed, and a dark s t a i n c o u l d be seen r a p i d l y On s e c t i o n i n g t h e p l a t e , i t was f o u n d t h a t bismuth  spread over t h e whole p l a t e under t h e oxide f i l m , presumably b y c g j p i l l a r y  a c t i o n s i n c e b i s m u t h w i l l wet u n p r o t e c t e d  The  aluminum.  f o u r t h specimen was s e a l e d b y immersing i n b o i l i n g water f o r  t h i r t y minutes a f t e r a n o d i z i n g .  When t e s t e d , t h e oxide f i l m was p e n e t r a t e d  and bismuth s p r e a d under t h e f i l m , c a u s i n g e x t e n s i v e c r a c k i n g i n t h e t h i c k oxide  D.  film.  D i s c,u s s i1o n o f R e s u l t s The  r e s u l t s have shown t h a t t h e a t t a c k on aluminum b y l i q u i d b i s m u t h  o c c u r r e d i n two ways. spreading  When p e n e t r a t i o n o f t h e oxide f i l m l e d t o immediate  o f t h e bismuth under t h e f i l m , i t was thought a t f i r s t  t h a t t h i s was  caused b y r a p i d s o l u t i o n o f t h e s u r f a c e o f t h e u n d e r l y i n g aluminum. I f , however, t h e b i s m u t h was d i s s o l v e d o f f t h e p l a t e , i t was f o u n d t h a t a t t a c k on the aluminum was c o n f i n e d t o a s m a l l a r e a around a b r e a k i n t h e o x i d e  film.  I n p l a c e s where access b y f r e s h bismuth was l i m i t e d , t h e r a t e o f a t t a c k was v e r y slow, due t o t h e s m a l l s o l u b i l i t y o f aluminum i n b i s m u t h (about a t 500 C)  .  1$  F o r bismuth t o t r a v e l up t o l / 2 i n c h under an unbroken oxide  film,  a t t h e r a t e observed, b y d i s s o l v i n g t h e aluminum would, t h e r e f o r e , be improbable.  I f , however, t h e oxide f i l m had a l r e a d y s e p a r a t e d  from t h e a l u m i -  num t h e b i s m u t h c o u l d r a p i d l y s p r e a d under t h e f i l m b y c a p i l l a r y a c t i o n .  - 48 The c o e f f i c i e n t o f t h e r m a l expansion o f an anodic f i l m on aluminum' is  approximately  i s heated,  one f i f t h  o f t h a t o f t h e "base m e t a l . When an a n o < l i  ze(  a c o n s i d e r a b l e shear s t r e s s w i l l o c c u r a t the m e t a l / o x i d e  l plate interface.  T h i s s t r e s s c o u l d produce a s e p a r a t i o n o f t h e m e t a l and o x i d e a l o n g t h e face.  Furthermore,  due t o d e h y d r a t i o n . of  the s t r e s s w i l l be i n c r e a s e d by  s h r i n k a g e o f the  oxide  I t i s p r o b a b l e t h a t t h i s c o n d i t i o n o c c u r r e d i n many  the p l a t e s t e s t e d .  As would be  expected t h i s phenomenon was  among t h e p l a t e s w i t h t h i c k o x i d e f i l m s .  more p r e v a l e n t  These p l a t e s would a l s o be more  s u s c e p t i b l e t o c r a c k i n g o f t h e f i l m under t h e s t r e s s , which would for  inter-  account  t h e v e r y r a p i d breakdown and r e m o v a l o f the oxide f i l m i n some c a s e s .  T h i s was  demonstrated b y the p l a t e t h a t was  a l l o w e d t o heat up b e f o r e  m e r s i o n i n t h e b i s m u t h and whose o x i d e f i l m f l o a t e d o f f as the p l a t e immersed f o r t h e f i r s t  imwas  time.  The performance o f a n o d i z e d p l a t e s t h a t were not a t t a c k e d i n t h i s way  c o n s t i t u t e d f u r t h e r evidence i n support o f the s e p a r a t i o n o f t h e  from t h e aluminum under t h e r m a l s t r e s s . sponsible f o r the s e p a r a t i o n o f the f i l m ,  oxide  I f t h e a c t i o n o f b i s m u t h was  re-  s e p a r a t i o n would o c c u r whenever  the bismuth p e n e t r a t e d t h e f i l m under c o n d i t i o n s t h a t l e d . t o s e p a r a t i o n on other p l a t e s .  However, some p l a t e s were a t t a c k e d under t h e s e c o n d i t i o n s and  were d i s s o l v e d i n a number o f p l a c e s w i t h o u t any s p r e a d i n g o f b i s m u t h under the f i l m  (see F i g u r e s 20 and  21).  I t would appear t h a t t h e removal o f t h e oxide f i l m i n t h e b i s m u t h o r t h e s p r e a d i n g o f t h e b i s m u t h under the f i l m , was consequence o f t h e a t t a c k on aluminum b y l i q u i d bismuth, t h e r m a l s t r e s s e s i n d u c e d by h e a t i n g the p l a t e .  The  not a d i r e c t  but r a t h e r of the  s e p a r a t i o n o f the  from t h e aluminum a l l o w e d t h e bismuth t o r u n between the m e t a l when i t p e n e t r a t e d the  film.  liquid  and the  oxide oxide  - 4 9  When p l a t e s t h a t had were examined, i t was  o n l y been a t t a c k e d b y p i t t i n g o r edge a t t a c k  n o t i c e d t h a t t h e a t t a c k was  concentrated  d i s c r e t e p o i n t s on t h e s u r f a c e or edges o f the p l a t e . -were o n l y two  or t h r e e such p o i n t s .  observed i n these  experiments.  c h e m i c a l l y and no The  c o n s i s t e n t w i t h the t h e o r y t h a t f l a w s were p r e s e n t which t h e b i s m u t h  On some p l a t e s  there  As mentioned p r e v i o u s l y , i t i s e x t r e m e l y  u n l i k e l y t h a t b i s m u t h c o u l d a t t a c k aluminum oxide any r e a c t i o n was  a t a number o f  evidence  type o f a t t a c k n o t e d  was  i n the oxide l a y e r through  penetrated.  48 S t e r n and U h l i g  , have a l s o p o s t u l a t e d t h a t aluminum i s a t t a c k e d  t h r o u g h f l a w s i n t h e oxide f i l m . been a n o d i z e d  i n ammonium  They s u b j e c t e d aluminum p l a t e s , t h a t  t a r t r a t e and  s u l p h u r i c a c i d , to a t t a c k by  carbon t e t r a c h l o r i d e . They f o u n d t h a t c o r r o s i o n d i d not the e n t i r e s u r f a c e o f the aluminum, b u t r a t h e r a t a few  boiling  start uniformly small points.  a l s o present  Edge  i n some specimens.. These r e s u l t s a l s o i n d i c a t e t h e  presence of d e f e c t s i n the oxide  film.  On examining p l a t e s w i t h thick ,, a n o d i z e d -  t o see d e f e c t s i n the f i l m . l i g h t area surrounding  over  Once  s t a r t e d , the r e a c t i o n s p r e a d r a d i a l l y u n t i l the c o r r o d i n g areas met. a t t a c k was  had  F i g u r e 22  oxide l a y e r s . i t was  possible  shows a h o l e i n the o x i d e f i l m ,  the  t h e h o l e i s an a r e a o f oxide t h a t has been l i f t e d o f f  the u n d e r l y i n g bismuth l a y e r .  F i g u r e 23  shows, i n s e c t i o n , a h o l e t h r o u g h the oxide l a y e r  ( c i r c l e d ) . There i s b i s m u t h above and below the oxide l a y e r . i s a t "the bottom 'of •" the photograph.  The  aluminum  of  FIGURE 22. P l a t e 32 (anodized i n 15$ HgSO^ and s e a l e d ) a f t e r immersion i n l i q u i d "bismuth f o r 20 minutes a t 500°C, showing a h o l e i n a r e g i o n o f r a i s e d o x i d e . M a g n i f i c a t i o n 60X.  FIGURE 23. S e c t i o n o f p l a t e 32 (anodized i n 15$ H 2 S0^ and s e a l e d ) a f t e r immersion i n l i q u i d bismuth f o r 20 minutes a t 500°C, showing a d e f e c t i n t h e oxide f i l m . M a g n i f i c a t i o n 1200X.  - 51 The c o u l d he  d e f e c t s i n the oxide f i l m c o u l d he  of s e v e r a l types.  They  areas where t h e f i l m i s v e r y t h i n , such as sharp edges on t h e p l a t e ,  s c r a t c h e s or p i t s i n t h e s u r f a c e .  P a r t i c l e s embedded i n the s u r f a c e  during  r o l l i n g or p o l i s h i n g , or n o n - m e t a l l i c  i n c l u s i o n s i n t h e m e t a l i t s e l f would  l e a d t o d i s c o n t i n u i t i e s i n the f i l m .  Concentrations  the s u r f a c e would produce areas film. areas  of i m p u r i t y atoms  on  o f the oxide o f t h e i m p u r i t y element i n t h e  I f t h e i m p u r i t y element was  r e a d i l y a t t a c k e d by l i q u i d bismuth,  o f i m p u r i t y o x i d e would a l l o w p e n e t r a t i o n by the b i s m u t h .  the oxide f i l m , e i t h e r t h e r m a l l y or m e c h a n i c a l l y  induced,  these  Cracks i n  would l e a d t o r a p i d  penetration.  A t h i r d s e r i e s o f experiments was on t h e a c t u a l p e n e t r a t i o n o f the f i l m . o f as many o f the sources s p o n s i b l e c o u l d be  designed  I t was  t o g i v e more i n f o r m a t i o n  hoped t h a t by the e l i m i n a t i o n  o f d e f e c t s as p o s s i b l e , t h e type o f d e f e c t r e -  determined.  The  S e s s i l e drop method was  chosen t o e l i m -  i n a t e edge d e f e c t s , and t o a l l o w the bismuth t o be p o s i t i o n e d on or away from v i s i b l e d e f e c t s i n the p l a t e .  - 52 EXFERIMMTAL - P a r t 3  IV.  S e s s i l e Drop Experiments  A s m a l l lump o f b i s m u t h was p l a c e d on a t h i n aluminum p l a t e and h e a t e d i n a tube f u r n a c e . f i l m was n o t e d .  The time a t which t h e bismuth p e n e t r a t e d t h e o x i d e  T h i s method had t h e advantage t h a t o n l y a s m a l l a r e a o f t h e  p l a t e was a t t a c k e d and t h e b i s m u t h c o u l d b e p l a c e d on o r away from obvious defects.  A l s o , f o u r p l a t e s c o u l d be t e s t e d a t t h e same t i m e .  A.  D e s c r i p t i o n o f Apparatus  l)  The tube f u r n a c e  A c o n v e n t i o n a l tube f u r n a c e was used; i t was 15 .inches l o n g and had a 1 i n c h i n t e r n a l diameter V y c o r tube, 36 i n c h e s l o n g , r u n n i n g t h r o u g h i t (see  f i g u r e 24).  One m o d i f i c a t i o n was made b y b l o c k i n g t h e t o p h a l f o f t h e  f u r n a c e up l / 4 i n c h t o p r o v i d e a 5 i n c h . l o n g s l o t a e r o s s t h e f u r n a c e , g i v i n g a view through t h e t u b e .  This slot  enabled the p l a t e s t o he observed w i t h -  out  d i s t u r b i n g the tube.  An i l l u m i n a t e d w h i t e background was p l a c e d b e h i n d  the  s l o t t o throw t h e drops o f b i s m u t h on t h e p l a t e s i n t o s i l h o u e t t e .  The  tube, complete w i t h p l a t e s , c o u l d be withdrawn t o a l l o w c l o s e r e x a m i n a t i o n of t h e s u r f a c e o f t h e p l a t e s .  A g r a p h i t e b o a t , 5 i n c h e s l o n g and o f a s e m i - c i r c u l a r h e l d f o u r aluminum p l a t e s .  cross-section,  A chromel-alumel thermocouple i n a s i l i c a  was p o s i t i o n e d over t h e g r a p h i t e b o a t i n t h e c e n t r e o f t h e f u r n a c e .  sheath The  thermocouple was .connected t o t h e Wheelco temperature c o n t r o l l e r u s e d i n the  p r e v i o u s experiments.  The f u r n a c e element was connected t o t h e mains  through a V a r i a c and a r e l a y .  The r e l a y was o p e r a t e d b y t h e temperature  Tube Furnace  FIGURE 2h,  P a r t i a l s e c t i o n of tube f u r n a c e .  - 54 -  controller.  The temperature  over t h e c e n t r e 4 i n c h e s o f t h e f u r n a c e v a r i e d no  more t h a n 10°C from t h e s e t temperature.  P u r i f i e d hydrogen was p a s s e d t h r o u g h t h e tube from t h e r i g h t hand end t o t h e l e f t , where i t was b u r n t .  2)  Gas p u r i f i c a t i o n  Hydrogen was used f o r a l l t h e s e s s i l e drop experiments, a l t h o u g h t h e tube was f l u s h e d w i t h n i t r o g e n a t t h e b e g i n n i n g and end o f a r u n t o e l i m i n a t e t h e r i s k o f an e x p l o s i o n .  The hydrogen was p u r i f i e d , E S : b e f o r e , b y p a s s i n g  .through a c a t a l y t i c p u r i f i e r t o remove oxygen and m o l e c u l a r s i e v e s t o remove moisture.  A f l o w o f 1 c u b i c f o o t / h o u r was m a i n t a i n e d d u r i n g experiments. A  f a s t e r f l o w (3 c u b i c f e e t / h o u r ) was u s e d f o r f l u s h i n g o u t .  3)  Preparation of plates  G r e a t c a r e was t a k e n i n t h e p r e p a r a t i o n o f t h e p l a t e s t o p r e v e n t t h e incorporation of defects.  I n some cases i t was f o u n d t h a t d i s s o l v e d  caused b l i s t e r i n g o f p a r t i a l l y r o l l e d sheet during a n n e a l l i n g .  hydrogen  To remove  hydrogen t h e aluminum was r e m e l t e d and c a r b o n rods soaked i n c a r b o n t e t r a c h l o r i d e were d i p p e d i n t o t h e m o l t e n m e t a l . s l a b i n a copper mold. before r o l l i n g .  The aluminum was c a s t as a f l a t  The s u r f a c e was machined t o remove any t h i c k o x i d e  New r o l l s were u s e d and g r e a t c a r e was t a k e n t o p r e v e n t  b e i n g r o l l e d i n t o t h e s u r f a c e o f t h e aluminum. mediate and a f i n a l a n n e a l a t sheet was Q*25 mm.  550°C  grit  The sheet was g i v e n an i n t e r -  f o r one hour.  The f i n a l t h i c k n e s s o f t h e  The sheet was c u t i n t o p l a t e s 2.4 cms square.  " S u p e r p u r i t y " aluminum o n l y was u s e d f o r t h e s e s s i l e drop A l l p l a t e s were c h e m i c a l l y p o l i s h e d and a n o d i z e d .  experiments.  Various eleetropolishing  - 55 s o l u t i o n s were tested, b u t the b e s t s u r f a c e f i n i s h was g i v e n b y c h e m i c a l polishing.  However, i t was n o t p o s s i b l e t o o b t a i n a p l a t e c o m p l e t e l y  of p i t s w i t h any method. phosphoric a c i d ,  free  A l c o a B r i g h t D i p was u s e d c o n s i s t i n g o f 80$  14$ a c e t i c a c i d and 6$ n i t r i c a c i d .  The p l a t e s were immersed  f o r about 10 minutes a t 70 - 80°G.  The p l a t e s were a n o d i z e d i n t h e ammonium t a r t r a t e  electrolyte . o  described i n the introduction.  A non-porous f i l m w i t h a t h i c k n e s s o f 14 A p e r  a p p l i e d v o l t i s o b t a i n e d a f t e r a n o d i z i n g f o r 12 minutes. wast\ed i n water, a l c o h o l and acetone,  and t h e n driedj.  The p l a t e s were  They were kept i n a  dessicator u n t i l required. D e f e c t s were d e l i b e r a t e l y I n t r o d u c e d m e c h a n i c a l l y i n some p l a t e s e i t h e r b e f o r e o r a f t e r a n o d i z i n g t o determine  t h e i r e f f e c t on t h e p e n e t r a -  t i o n o f t h e bismuth.  B.  E x p e r i m e n t a l Proqedure  S m a l l lumps o f bismuth,  a p p r o x i m a t e l y 2.5  mm  i n diameter,  were  washed i n d i l u t e n i t r i c a c i d t o remove any o x i d e ; t h e y were then washed i n water, acetone  and d r i e d .  F o u r aluminum p l a t e s w i t h t h e same f i l m t h i c k n e s s  were p l a c e d on t h e g r a p h i t e b o a t .  One lump o f bismuth was p l a c e d on each  p l a t e i n a p r e v i o u s l y s e l e c t e d p o s i t i o n , e i t h e r on o r away from any v i s i b l e defects.  The b o a t was pushed t o t h e c e n t r e o f t h e f u r n a c e and t h e thermo-  couple was i n s e r t e d i n t h e tube so t h a t i t was above t h e c e n t r e o f t h e b o a t .  The  f u r n a c e tube was f l u s h e d w i t h n i t r o g e n f o r 20 minutes and hydroo  gen f o r 30 minutes b e f o r e t h e f u r n a c e was s w i t c h e d on. was used f o r a l l experiments,  t h i s temperature  a f t e r s w i t c h i n g on t h e f u r n a c e .  A temperature  o f 500 C  b e i n g r e a c h e d about 10 minutes  - 56 The bismuth lumps melted, and formed n e a r l y s p h e r i c a l drops (see F i g u r e 25), no w e t t i n g o f t h e o x i d e o c c u r r i n g .  With o n l y one or two  excep-  t i o n s , the s u r f a c e s of the drops were c l e a n and f r e e from o x i d e , and remained t h i s way  f o r the d u r a t i o n of the longest t e s t  FIGURE 25  (75 h o u r s ) .  S e c t i o n o f bismuth drop on p l a t e D4 (140 $ oxide f i l m ) , g e n e r a l shape o f d r o p s . MagnJ.fication 20 X.  showing  The bismuth drops were examined t h r o u g h t h e s l o t i n the f u r n a c e e v e r y f i v e minutes f o r t h e f i r s t houn , and t h e r e a f t e r a t i n c r e a s i n g vals.  I f p o s s i b l e , t h e f u r n a c e tube was  q u i c k l y withdrawn  Inter-  every hour t o  examine the s u r f a c e o f the p l a t e s . I n n e a r l y every case, however, p e n e t r a t i o n of the f i l m was  i n d i c a t e d by the bismuth drop r a p i d l y f a l l i n g , the bismuth  s p r e a d i n g over the s u r f a c e o f the p l a t e under the oxide f i l m .  C.  Analysis of Results  D e t a i l s o f a l l p l a t e s t e s t e d , i n c l u d i n g f i l m t h i c k n e s s , the time taken f o r the bismuth t o p e n e t r a t e t h e f i l m , and comments on the form o f attack  a r e g i v e n i n Appendix I I .  - 57 Once a g a i n t h e r e were wide v a r i a t i o n s i n t h e time t a k e n b y t h e b i s m u t h t o p e n e t r a t e t h e oxide f i l m .  I n many c a s e s , p e n e t r a t i o n was f o l l o w e d by im-  mediate s p r e a d i n g o f t h e bismuth under t h e oxide f i l m , a g a i n i n d i c a t i n g .that the f i l m had s e p a r a t e d from t h e aluminum even though the r a t e o f h e a t i n g was  much,  lower t h a n i n p r e v i o u s experiments.  I n a few c a s e s , however, t h e bismuth  took s e v e r a l hours t o s p r e a d showing t h a t s e p a r a t i o n had not o c c u r r e d .  I n f o u r cases, t h e bismuth was p l a c e d so t h a t i t c o v e r e d one o r more s m a l l p i t s on t h e s u r f a c e o f the p l a t e s .  Once, the bismuth p e n e t r a t e d  the f i l m b e f o r e 500°C was reaqhed, i n d i c a t i n g a d e f e c t t h a t went  completely  through the f i l m .  The o t h e r f i l m s were n o t p e n e t r a t e d a f t e r 7h 3/k  28 hours and 8^ 1/2  hours ( i n the l a t t e r case, a l l p l a t e s were p e n e t r a t e d  when t h e temperature  550°c).  c o n t r o l r e l a y jammed and t h e temperature  hours,  went t o over  P l a t e s w i t h no v i s i b l e d e f e c t s were a t t a c k e d a f t e r times v a r y i n g  from K7 minutes t o 9 hours 45 minutes.  I t would appear t h a t d e f e c t s t h a t can  be seen w i t h t h e u n a i d e d eye ( o r a m a g n i f y i n g g l a s s ) do not lower t h e p r o t e c t i v e power o f t h e f i l m .  ( F i n e c r a c k s or pores  i n the f i l m i t s e l f  cannot  be seen even under h i g h m a g n i f i c a t i o n as the oxide f i l m i s t r a n s p a r e n t ) .  Two p l a t e s had v e r y sharp p i t s i n t r o d u c e d w i t h a s t e e l one b e f o r e and one a f t e r a n o d i z i n g . same t i m e .  scriber,  Both p l a t e s were a t t a c k e d a t about t h e  S i m i l a r l y , two p l a t e s were s c r a t c h e d w i t h a s t e e l s c r i b e r , o n e b e f o r e  and one a f t e r a n o d i z i n g .  The p l a t e s c r a t c h e d .before a n o d i z i n g was a t t a c k e d  a f t e r 9 hours, the one a f t e r a n o d i z i n g was u n a t t a c k e d a f t e r 12 l / 2 h o u r s . I n a l l cases t h e bismuth was p l a c e d on t h e d e f e c t .  I t would appear t h a t  exposure t o the atmosphere h e a l e d t h e b r e a k i n the f i l m p r o v i d i n g p r o t e c t i o n as good as t h a t o f the a n o d i z e d  film.  - 58 Two p l a t e s were s e v e r e l y deformed b y b e n d i n g through a 5/l6  i n c h diameter r o d t o c r a c k t h e f i l m .  l80°  The p l a t e s were t h e n f l a t t e n e d  and a drop o f bismuth p l a c e d on what was the o u t s i d e o f t h e bend. were p e n e t r a t e d a f t e r 37 and 67 minutes.  over  The f i l m s  Of t h e two c o n t r o l p l a t e s , one  f a i l e d a f t e r k7 minutes, t h e o t h e r was u n a t t a c k e d a f t e r lh  hours.  o Four p l a t e s were p r e p a r e d w i t h a 700 A oxide f i l m . t h a t f i l m s o f t h i s t h i c k n e s s might by h e a t i n g .  I t was  thought  c r a c k under t h e t h e r m a l s t r e s s e s i n d u c e d  I f c r a c k i n g o c c u r r e d , i t would almost c e r t a i n l y be d u r i n g the  h e a t i n g o f the p l a t e .  None o f t h e p l a t e s , however, showed any p e n e t r a t i o n  by bismuth a f t e r 20 h o u r s . o I t w i l l be n o t i c e d t h a t two p l a t e s  (ihO  A f i l m s ) were u n a t t a c k e d  a f t e r 7h hours and t h r e e (280 A f i l m s ) a f t e r 28 h o u r s .  On s e c t i o n i n g t h e 7h  hour p l a t e s through the bismuth drop, no s i g n o f a t t a c k o r c h e m i c a l a c t i o n c o u l d be seen. U n f o r t u n a t e l y , i t was i m p r a c t i c a l t o c a r r y out t e s t s f o r l o n g e r p e r i o d s than 75 h o u r s .  The o n l y mechanism, however, b y which t h e bismuth  c o u l d p e n e t r a t e t h e o x i d e f i l m i n times o f t h i s o r d e r , would be by d i f f u s i o n o f bismuth atoms through t h e aluminum o x i d e f i l m .  To see i f the d i f f u s i o n  o f bismuth through the f i l m was a p r o b a b l e mechanism, t h r e e s a p p h i r e windows o f d i f f e r e n t o r i e n t a t i o n s were h e a t e d a t 500°C f o r hQ hours w i t h a l/h diameter drop o f bismuth on each.  The windows were washed q u i c k l y w i t h d i l u t e  n i t r i c a c i d t o remove any bismuth t h a t had condensed drops o f bismuth were knocked  inch  on t h e s u r f a c e .  The  o f f and the s u r f a c e o f the s a p p h i r e s p o l i s h e d  l i g h t l y w i t h B r a s s o t o remove any a d h e r i n g bismuth o r bismuth o x i d e .  The  a r e a under t h e bismuth drop was t h e n s p e c t r o g r a p h i c a l l y a n a l y s e d f o r bismuth.  - 59 None was found i n d i c a t i n g t h a t t h e bismuth had not d i f f u s e d i n t o sapphire.  the  I t i s , t h e r e f o r e , extremely u n l i k e l y t h a t t h e bismuth c o u l d  d i f f u s e through t h e aluminum oxide f i l m on t h e p l a t e s .  An a d d i t i o n a l s a p p h i r e window was h e a t e d w i t h t h e t h r e e p r e v i o u s l y mentioned.  T h i s window had no bismuth p l a c e d on i t , and was not c l e a n e d  before analysis.  A t r a c e o f bismuth ( l e s s t h a n 10 p. p. m.) was found,  i n d i c a t i n g t h a t a monolayer  o f bismuth h a d condensed on t h e p l a r e  o though t h e vapour p r e s s u r e o f bismuth a t 500 C I s l e s s t h a n 1 mm.  FIGURE 26  even Hg.  o D e f e c t i n o x i d e f i l m on p l a t e D2 (140 A f i l m ) a f t e r p e n e t r a t i o n by l i q u i d b i s m u t h . M a g n i f i c a t i o n 150 X.  On examining p l a t e s t h a t had been a t t a c k e d by t h e bismuth, i t was f o u n d t h a t t h e o x i d e f i l m was w r i n k l e d as i n p r e v i o u s t e s t s .  I n places the  bismuth t h a t had s p r e a d under t h e f i l m c o u l d be seen through a h o l e i n t h e  - 60 -  film  (see F i g u r e 26).  The o n l y e x p l a n a t i o n f o r t h e s e h o l e s i s t h a t t h e  bismuth had a t t a c k e d a weak p a r t o f t h e f i l m from below.  The o n l y type o f  d e f e c t t h a t would be s u s c e p t i b l e t o such a t t a c k i s an a r e a o f i m p u r i t y i n t h e aluminum oxide f i l m . the same as t h a t o f p i t s  The s u r f a c e d e n s i t y o f such h o l e s was  i n t h e f u l l y immersed p l a t e s .  oxide  approximately  > - 6l -  V. CONCLUSION  The r e s u l t s are d i s c u s s e d a t the ends o f t h e a p p r o p r i a t e e x p e r i m e n t a l sections.  The t e c h n i q u e o f measuring  the v a r i a t i o n o f c o n t a c t a n g l e w i t h  16 temperature  and time o f immersion  d i c a t e the breakdown  of  I n l i q u i d bismuth as u s e d by Raynor  the o x i d e  i c a l f o r use w i t h aluminum.  f i l m s on t r a n s i t i o n m e t a l s , was  to i n impract-  A d e c r e a s i n g c o n t a c t a n g l e d i d not i n d i c a t e a  g e n e r a l decrease, b u t an i n c r e a s e i n t h e number o f i s o l a t e d areas a t which w e t t i n g had o c c u r r e d . A l l o x i d e f i l m s produced on the aluminum were p r o t e c t i v e t o a l i m i t e d degree, w i t h t h e e x c e p t i o n o f t h o s e on e l e c t r o p o l i s h e d  specimens.  The l a t t e r p r o v i d e d no p r o t e c t i o n a g a i n s t t h e l i q u i d b i s m u t h .  T h i s was  to  49 be expected s i n c e G y - H o l l o ^ f o u n d the f i l m on e l e c t r o p o l i s h e d aluminum t o be b o t h t h i n and  porous.  The aluminum was pitting  a t t a c k e d b y the l i q u i d bismuth i n two ways, b y  on the s u r f a c e and edges o f the p l a t e s , and by bismuth  under the f i l m  ( i n some cases c a u s i n g i t t o f l o a t o f f ) .  p e r i m e n t a l e v i d e n c e t h a t the aluminum o x i d e i t s e l f was attack.  S e s s i l e drop experiments  spreading  There was  no  ex-  subjected to general  on a n o d i z e d p l a t e s and s a p p h i r e windows  showed t h a t bismuth does not d i f f u s e through the o x i d e f i l m under the  exper-  i m e n t a l c o n d i t i o n s employed.  The p i t t i n g type o f a t t a c k was and w i t h the t h i n n e r f i l m s . observed on each p l a t e . was  p r e v a l e n t a t t h e lower  temperatures  Only a s m a l l number o f p o i n t s o f a t t a c k was  The n a t u r e o f the a t t a c k i n d i c a t e d t h a t the  p e n e t r a t i n g the o x i d e f i l m through d e f e c t s .  S e s s i l e drop  bismuth  experiments  showed t h a t p i t s i n t h e aluminum under the oxide f i l m were not n e c e s s a r i l y sources  o f d e f e c t s i n t h e f i l m , and t h a t s c r a t c h e s t h r o u g h t h e f i l m q u i c k l y  h e a l e d i n a i r and d i d n o t  c o n s t i t u t e a weakness.  Mechanical  d e f e c t s i n the  p l a t e or f i l m do not d i m i n i s h the p r o t e c t i v e power o f t h e f i l m , w i t h e x c e p t i o n o f c r a c k s produced by l a r g e  I t i s most p r o b a b l e the aluminum. having  deformations.  that concentrations of i m p u r i t i e s e x i s t e d i n  These c o n c e n t r a t i o n s would l e a d t o areas  a composition  the  corresponding  of the oxide  t o t h e o x i d e o f the i m p u r i t y .  The  film main  i m p u r i t i e s i n t h e aluminum (see T a b l e IV) a r e copper, t i t a n i u m , magnesium and n i c k e l ,  o f t h e s e , copper and n i c k e l a r e a t t a c k e d by l i q u i d b i s m u t h a t  temperatures below 500°C, t h e i r oxides b e i n g r e d u c e d by b i s m u t h . c o n c e n t r a t i o n s cannot be  These  seen i n the p l a t e s u s e d i n the experiments even  under h i g h m a g n i f i c a t i o n , b u t much i n d i r e c t evidence  exists for their  presence.  50 Davis  has  found a d e n d r i t i c s t r u c t u r e i n the i n g o t from which  the p l a t e s were made, thus  s e g r e g a t i o n c o u l d be  expected  i s b e l i e v e d t h a t the r o l l i n g and a n n e a l i n g would not be the s e g r e g a t i o n  i n the i n g o t . s u f f i c i e n t to  It destroy  completely.  The A l c a n 2S p l a t e s w i t h a l l o y i n g a d d i t i o n s had many more p i t s than the e q u i v a l e n t  " s u p e r p u r i t y " aluminum p l a t e s .  S i n c e b i s m u t h cannot  a t t a c k o r d i f f u s e t h r o u g h a pure aluminum o x i d e f i l m , any d e f e c t i n such a f i l m would have t o go c o m p l e t e l y penetrate  immediately.  The  t h r o u g h the f i l m , and t h e bismuth c o u l d  f a c t t h a t some f i l m s were p e n e t r a t e d o n l y a f t e r  9 hours can o n l y be e x p l a i n e d on t h e b a s i s o f bismuth s l o w l y r e a c t i n g w i t h an a r e a o f i m p u r i t y  oxide.  - 63 The  second t y p e o f a t t a c k , where the bismuth  t h e o x i d e f i l m , was  s p r e a d r a p i d l y under  almost c e r t a i n l y caused b y t h e s e p a r a t i o n o f the aluminum  and i t s o x i d e a l o n g the o x i d e / m e t a l i n t e r f a c e .  Shear s t r e s s e s  resulting  from t h e d i f f e r e n c e i n the c o e f f i c i e n t o f t h e r m a l expansion o f aluminum and i t s o x i d e and from d e h y d r a t i o n o f the o x i d e f i l m , would be  generated  d u r i n g h e a t i n g o f t h e p l a t e , and would be g r e a t e r I n t h e t h i c k e r f i l m s .  Pene-  t r a t i o n o f t h e f i l m c o u l d o c c u r b y t h e mechanism j u s t d e s c r i b e d f o r p i t t i n g , by c r a c k i n g o f the f i l m a l o n g t h e edges o f t h e p l a t e where a s t r e s s r a i s e r o r c r a z e c r a c k i n g on t h e s u r f a c e o f the p l a t e .  exists,  - 6k VI.  RECOMMENDATIONS FOR FURTHER WORK  The r e s u l t s - o f t h e p r e s e n t  i n v e s t i g a t i o n a r e q u a l i t a t i v e and  s e v e r a l l i n e s o f i n q u i r y might he f o l l o w e d t h a t would r e i n f o r c e t h e p r e s e n t findings.  The r e s u l t s o f v a r y i n g t h e i m p u r i t y c o n t e n t o f t h e aluminum might  throw a d d i t i o n a l l i g h t on t h e mechanism o f p e n e t r a t i o n o f t h e f i l m b y l i q u i d bismuth.  I f t h e mechanism p o s t u l a t e d i n t h e p r e s e n t  investigation i s correct,  zone r e f i n e d aluminum, o r a t h i n aluminum f i l m condensed on a g l a s s  slide,  should e x h i b i t exceptional r e s i s t a n c e t o attack.  By v a r y i n g t h e o x i d e f i l m t h i c k n e s s and t h e r a t e o f h e a t i n g i t s h o u l d b e p o s s i b l e t o o b t a i n i n f o r m a t i o n on t h e bond s t r e n g t h between num and i t s o x i d e  film.  alumi-  - 65 VII.  A.  A l c a n 2S.  Temp. °C  Mechanically  Plate  Time  No.  Mins.  APPENDIX I  polished.  Type o f A t t a c k  4oo  2  50  S t a i n i n g and s l i g h t  450  4  40  3h  10  S t a i n i n g , bismuth a d h e r i n g t o p l a t e , s l i g h t a t t a c k at two p o i n t s on one edge. S t a i n i n g , bismuth a d h e r i n g , edge and s u r f a c e a t t a c k at many p o i n t s .  5  9  33  5  35  12  500  B.  S t a i n i n g , b i s m u t h a d h e r i n g , severe a t t a c k a t s u r f a c e l e v e l , s l i g h t a t t a c k a t two p o i n t s on one edge. S t a i n i n g , b i s m u t h a d h e r i n g , edge a t t a c k a t many points, surface p i t s . Bismuth a d h e r i n g , many s u r f a c e p i t s under bismuth, s l i g h t edge a t t a c k .  " S u p e r p u r i t y " Aluminum .  Temp* °C  Plate  Time  No.  Mins.  a t t a c k a l o n g one edge  Electropolished.  Type o f A t t a c k  350  11  0  Immediate w e t t i n g f o l l o w e d b y d i s s o l u t i o n o f t h e plate.  4oo  10  0  As  11.  450  7  0  As  11.  - 66 C.  " S u p e r p u r i t y " Aluminum.  Temp.  Plate  Time  Wo.  Mins.  Mechanically  polished.  Type o f A t t a c k °C  350  14  400  6  450  500  D.  S t a i n i n g , bismuth adhering,  43  edge a t t a c k .  ^—  18  63  8  10  9  8*  15  5  19  10  20  0  S t a i n i n g , bismuth a d h e r i n g , edge a t t a c k a t t h r e e points, surface p i t t i n g . S t a i n i n g , bismuth a d h e r i n g , s l i g h t edge a t t a c k at l i q u i d l e v e l . S t a i n i n g , f o l l o w e d b y edge a t t a c k a t many p l a c e s spreading t o surface o f p l a t e . As 8.. Q u i c k p e n e t r a t i o n o f f i l m , w i t h s p r e a d i n g under f i l m causing w r i n k l i n g , considerable d i s s o l u t i o n of p l a t e . S t a i n i n g , bismuth a d h e r i n g , l e a d i n g t o l i q u i d l e v e l a t t a c k and s p r e a d i n g o f bismuth under f i l m . Immediate p e n e t r a t i o n o f f i l m w i t h s p r e a d i n g under film. A t t a c k near t o p o f p l a t e .  " S u p e r p u r i t y " Aluminum.  A n o d i z e d i n 15$ H2SQJ4. f o r 30 m i n u t e s ,  ( f i l m thickness approximately  Plate  Time  No.  Mins.  400  30  180  Slight  500  31  300  No a t t a c k .  41  0  32  20  Temp.  slight  14 m i c r o n s )  Type o f A t t a c k °C  s t a i n i n g near l i q u i d l e v e l  - no a t t a c k .  Oxide removed on immersion o f bottom o f p l a t e , b i s muth s p r e a d under f i l m on unimmersed p a r t . S e a l e d f o r 30 mins. P e n e t r a t i o n and s p r e a d i n g o f b i s muth under f i l m w i t h c r a c k i n g o f f i l m and s o l u t i o n o f aluminum.  - 67 E.  " S u p e r p u r i t y " Aluminum.  Anodized  i n Ammonium T a r t r a t e  Temp..  Plate  Time  Film  °c  Wo.  Mins.  Thickness A  26  40  140  23  5  140  24  10  140  27  0  140  39  55  140  12  30  140  21  0  140  22  36  210  25  20  140  36  18  280  37  105  420  4o  175  280  1  350 4oo  450  500  0  .  Type o f A t t a c k  S l i g h t edge a t t a c k a t "bottom c o r n e r , ._,,„  Removal f i l mt h from fa t e plate, so o lfu oxide t i o n and i n n i nmost g of o pl C o n s i d e r a b l e edge a t t a c k a t one p o i n t . no o t h e r a t t a c k . Immediate w e t t i n g f o l l o w e d b y removal of oxide f i l m from most o f p l a t e . S l i g h t staining, very small area of edge a t t a c k . Complete removal o f o x i d e f i l m from most o f p l a t e - c o n s i d e r a b l e s o l u t i o n of aluminum. Immediate w e t t i n g w i t h removal o f o x i d e f i l m and s o l u t i o n o f aluminum. A t t a c k under p a r t s o f f i l m l e a d i n g t o detachment o f bottom o f p l a t e . Edge a t t a c k a t s e v e r a l p o i n t s near bottom o f p l a t e s p r e a d i n g Inwards. Removal o f oxide and s o l u t i o n over s m a l l a r e a a t bottom o f p l a t e . Bismuth a d h e r i n g t o c e n t r e o f p l a t e w i t h p i t s underneath. S m a l l amount o f bismuth a d h e r i n g , f o l lowed b y complete removal o f oxide f i l m  1  - 68 -  APPENDIX I I .  A l l p l a t e s were o f " s u p e r p u r i t y " aluminum,  c h e m i c a l l y p o l i s h e d , and o  a n o d i z e d i n ammonium t a r t r a t e s o l u t i o n f o r 12 minutes (10 minutes f o r 70 A f i l m s ) .  Temperature o f t e s t i n each case was 500°C. Film Time t o Plate No. C 1  o Thickness A  70  Comments Penetrate  3 hrs. 8 1/2 h r s .  R e l a y j ammed,T > 550°C.  8 1/2 h r s .  As C 2.  8 .1/2 h r s .  As C 2.  14 h r s . +  No a t t a c k .  E 2  37 mins.  Mechanically  cracked.  E  3  47 mins 0  E  4  67 mins.  Mechanically  cracked.  C 2 C  3  C 5 E 1  70  Bismuth p l a c e d on p i t i n plata„  - 69 -  Plate No. A  3  Film o Thickness A 140  9 3/4 h r s .  A  5  3 1/2 h r s .  A  6  9 3/4 h r s .  D 2  140  Comments  Penetrate  5 mins.  A 4  :  Time t o  5 hrs.  P e n e t r a t i o n b e f o r e 500°C r e a c h e d . . B i s muth drop on f i n e p i t s i n p l a t e . t  Bismuth p e n e t r a t e d and s p r e a d s l o w l y under f i l m over a p e r i o d o f 24 h o u r s . As D 2. V e r y l i t t l e a t t a c k on aluminum.  D  3  4 hrs.  D  h  74 3/4 h r s . plus 74 3/4 h r s . plus  No- a t t a c k . in plate. No a t t a c k .  ^5 h r s .  Mechanically p i t t e d before anodizing, bismuth p l a c e d on p i t . Mechanically p i t t e d a f t e r anodizing, bismuth p l a c e d on p i t . Plate scratched before anodizing, b i s muth c l o s e t o s c r a t c h . Plate scratched a f t e r anodizing, b i s on s c r a t c h . No a t t a c k .  D 5  K 1  140  K 2  a/5 h r s .  3  A/9 hrs •  K  K 4  12 1/2 h r s . plus  Bismuth drop on f i n e  pits  - TO -  ' Plate Wo. B.  1  Film Thickness  280  Time t o o A  Comments Penetrate  28 1/3  hrs. hrs.  No a t t a c k . plate. No a t t a c k .  hrs.  3 hours t a k e n f o r b i s m u t h t o s p r e a d film. No a t t a c k .  plus  2  28 1/3  B  3  plus 5 hrs.  B  k  B  28 1/3  Bismuth drop on s m a l l p i t i n  plus  700  20 h r s . +  No  2  20 h r s . +  20 h o u r s .  3  20 h r s . +  f i l m had o c c u r r e d , p e n e t r a t i o n would  H k  20 h r s . +  have t a k e n p l a c e w i t h i n a few  H  1  H H  under  a t t a c k on any  o f the f o u r p l a t e s a f t e r  I f thermal cracking of  the  hours.  - 71 ~ VIII.  BIBLIOGRAPHY  1.  H a c k e t t , H. N.  2.  Smith, A. R. and Thompson, E . S.  T r a n s . Am. Soc. Mech. Engrs.,  64, 6kl ( l 4 2 ) . 9  T r a n s . Am. Soc. Mech. E n g r s . , 64,  625 (1942). 3-  Heron, S. D.  U. S. P a t e n t 1670965, May 22, 1928.  4.  Bennett, F . C.  5-  Chirkin,  J . N u c l . Energy, 5, 124  6.  Novikov,  J . N u c l . Energy, 4, 385 (1957).  7.  Lyon, R. N.  14854, Oct. 1948.  Dow C h e m i c a l Co., Report (1957).  ' l i q u i d M e t a l s Handbook".  U. S. A. E . C.  Rep. Ko. NAVEXOS  P-733 (1952) Ch. 2 . 8.  Boadle.  9.  Frost.  Atomics, 8 , 4 l and 83 (1957). N u c l . Eng.,  1,  33k and 373 (1956).  10.  B a i l e y , Fox and Watkins.  U. K. A. E . R. E . Rep. No. M/TN6 ( l 5 l ) .  11.  Bondi.  12.  Hansen.  13.  Frost et a l .  14.  A d d i s o n , A d d i s o n , K e r r i d g e and Lewis.  15.  I b e r s o n , E . Ph. D. T h e s i s , Nottingham  16.  Raynor, J . B. Ph. D. T h e s i s , Nottingham  17.  H a r k i n s and Brown. J . A. C. S.  18.  Parkman and Shepard.  19.  B a r t o n , P. J . and Greenwood, G. W.  20.  T e i t e l , R. J . e t a l . N u c l e o n i c s , 12 ( 7 ) , 14 (1954).  21.  Greenwood, G. W. and Sharpe, B.  A. E . R. E . Rep. M/R  22.  Graham, L . W. and W i l s o n , G. W.  J . Iron St. Inst.  23.  Weeks, J . R. e t a l .  9  Chem. Revs., 52, 4 l 7 (1953). "Constitution of Binary A l l o y s " .  (McGraw-Hill  2nd Ed. 1958).  P e a c e f u l Uses o f Atomic Energy, Paper P/27O (1958). J . C. S . 1454 (1956). (1959). (1959).  4 l , 499 (1919).  U. S . A. E . C.  Rep. No. ORO-45 (1951).  J . I n s t . Met.  86, 504 (1957-58).  2250 (1954).  193 P t I I , 103 (1959)  P r o c . I n s t . Conf. P e a c e f u l Uses Atomic  (Geneva 1955) 9, 3^1.  Energy  -  24.  Dawe, D.. .W., 2 7 1  P a r r y , G. I . and W i l s o n , G. W.  7 2  190,  J . Iron'St. Inst.  ( 1 9 5 8 ) .  Gulbransen,  2 6 o  R i c h a r d s o n , F . D. and J e f f e s , J .  2 7 .  Hass, G.  2 8 .  K e l l e r , F . and Edwards, J . D.  2 9 .  P r e s t o n , G. D. and Bircumshaw, L . L. P h i l . Mag.  3 0 .  de Brouchere,  3 1 .  Raether, H.,C. R. Acad. S c i . , P a r i s ,  3 2 .  W i l s d o r f , H. G. F .  3 3 -  C a b r e r a , N. and Mott, N.  34.  Mott, N. F . T r a n s . F a r a d . Soc. 3 5 , 1 1 7 5 .  35°  H a r r i n g t o n , R. A. and N e l s o n , H. R. T r a n s . Amer. I n s t . M i n . Met. Eng. 1 3 7 , 1 2 8 (1940).  36.  Kubaschewski, 0 . and Hopkins, B. E . ( B u t t e r w o r t h ' s 1 9 5 3 ) p. 1 3 1 .  37.  Vernon, W. H. J .  3 8 .  Hunter, M. S. and Fowle, P.  39-  S t e i n h e i l , A.  40.  Hass, G.  41.  Hunter, M. S. and Fowle, P.  42.  Hunter, M. S. and Towner, P. F .  43.  Kelman, e t a l .  44.  Kubaschewski,  4 5 .  A d d i s o n , C. C , I b e r s o n , E . and Raynor, J . B.  Z. Anorg. Chem., 254,  L.  9 6  J . I n s t . Met.  ( 1 9 V 7 ) .  1 6 0 ,  2  6  l  ( 1 9 4 8 )  ( 1 9 V ? ) .  I n t . Conf. S u r f . R e a c t , p .  7 1 ,  1247  2 2 7 ,  l  6  8  2 2 ,  6 5 4  2 0 2  (1948).  ( 1 9 3 6 ) .  (1945).  1 3 1  Nature, London,  ,  6  0  0  (1948).  ( l 9 5 l ) .  F. Rep. P r o g r . Phys. 12,  1 6 3  (1948-49).  " O x i d a t i o n o f M e t a l s and A l l o y s "  Trans. Farad. S o c , 2 3 , 1 1 7 . J . Electrochem. Soc. 1  J . O p t i c a l Soc. Amer.  3 9 ,  ( 1 9 5 6 )  .  (1934). 5 3 2  ( 1 9 4 9 ) .  0 1 ,  J . E l e c t r o c h e m . Soc Rep. No. ANL-4417  Z. E l e k t r o c h e m .  482  0 3 ,  J . Electrochem. Soc. 1  U. S. A. E . C. .  5_1,  H. E . J . I r o n S t . I n s t .  Ann. F h y s i k , 1 9 , 4 6 5  0  <J. Phys. Chem.  kh,  1 5 2  kdl  ( 1 9 5 4 ) .  1 0 8 ( 2 ) ,  1 3 9  ( 1 9 6 1 ) .  9 6  ( 1 9 5 8 ) .  ( 1 9 5 0 ) .  ( 1 9 3 8 ) .  Chem. and I n d .  "'Linde' m o l e c u l a r s i e v e s f o r s e l e c t i v e a d s o r p t i o n " (B.-D. H. L t d . , Poole,  47.  E . A. and Wysong, W. S.  IO87  2 5 .  46.  -  England).  Bircumshaw, L . L .  P h i l . Mag. 12,  5 9 6  ( 1 9 3 1 ) •  - 73 48.  StejrrijM. and U h l i g , H. H.  49.  G y - H o l l o ' Mme  M.  50.  D a v i s , K. G.  U n i v e r s i t y o f B r i t i s h Columbia.  51.  Spooner, R. C.  J . E l e c t r o c h e m . Soc.  99, 381  Memoires S c i e n t i f i c de l a Rev. Met.  J . E l e c t r o c h e m . Soc.  Private  102, 156 (1955).  and  389 (1952).  57, 23 (i960). communication.  

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0105831/manifest

Comment

Related Items