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An investigation of the nature of changes in electrode potential produced by uni-directional stress Dudley, Robert Stanley 1951

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.. J W r .AN INVESTIGATION OF THE NATURE OF CHANGES IN ELECTRODE POTENTIAL PRODUCED BY UNI-DIRECTIONAL STRESS by ROBERT STANLEY DUDLEY A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF APPLIED SCIENCE IN CHEMICAL ENGINEERING In the Department of Chemistry We accept this thesis as conforming to the standard required from candidates for the degree of MASTER OF APPLIED SCIENCE. Members of the Department of Chemistry THE UNIVERSITY OF BRITISH COLUMBIA A p r i l , 1951 i i ABSTRACT The e f f e c t o f , u n i d i r e c t i o n a l s t a t i c s t r e s s on me e l e c t r o d e p o t e n t i a l o f copper was s t u d i e d . S t u d i e s were made w i t h b o t h s o f t copper and c o l d drawn copper i n s o l u t i o n s o f copper s u l p h a t e and s e v e r a l o t h e r e l e c t r o l y t e s . The change i n magnitude o f the e l e c t r o d e p o t e n t i a l was f o u n d t o depend on s e v e r a l v a r i a b l e s , t i m e , t e m p e r a t u r e , s t r e s s p e r u n i t a r e a , c o n c e n t r a t i o n of s o l u t i o n and the e l e c t r o l y t e i n s o l u t i o n . Measurement, w h i c h was made i n most i n s t a n c e s w i t h a Leeds and N o r t h r u p p o t e n t i o m e t e r , was between s t r e s s e d and u n s t r e s s e d p a i r s o f copper w i r e . S t r e s s was a p p l i e d by a t t a c h i n g a s c a l e pan t o one o f the w i r e s and a p p l y i n g w e i g h t s t o the pan. Two main c o n c l u s i o n s can be drawn f r o m the r e s u l t s o b t a i n e d . (1) S t r a i n p o t e n t i a l i s the r e s u l t o f two s e p a r a t e e f f e c t s . The f i r s t e f f e c t t h a t of the r u p t u r e o f a s u r f a c e f i l m i s the dominant e f f e c t , b u t the second e f f e c t t h a t o f the change i n i n t e r n a l energy due t o p l a s t i c d e f o r m a t i o n cannot be d i s c a r d e d . (2) S t r a i n p o t e n t i a l cannot be i g n o r e d as a f a c t o r i n c o r r o s i o n p r o b l e m s . I t has been shown t h a t a s t r e s s o f 992 kgm/cm 2 can cause a p o t e n t i a l change i n the more anodic or a c t i v e d i r e c t i o n of over 50 mv. I f s t r e s s i s a p p l i e d t o a non-homogeneous m e t a l system some p o t i o n s o f the system w i l l be under p l a s t i c s t r a i n w h i l e o t h e r s w i l l p o s s i b l y be under p l a s t i c s t r a i n . The p l a s t i c s t r a i n a r e a s , w h i c h would u s u a l l y be s i t u a t e d a t g r a i n b o u n d a r i e s , would t h e r e f o r e be more a c t i v e and h i g h l y s u s c e p t i b l e t o c o r r o s i o n . i i i . F a i l u r e o f the m e t a l c o u l d t h e n be c a u s e d by s t r e s s c o n c e n t r a t i o n or by the g r a d u a l c o r r o s i o n o f the g r a i n b o u n d a r i e s of the m e t a l system. i . ACKNOWLEDGEMENT I w i s h t o thank Dr. L. W. S h e m i l t and Mr. W. McPadden f o r the v e r y v a l u a b l e a s s i s t a n c e g i v e n . Thanks are a l s o due t o the N a t i o n a l R e s e a r c h C o u n c i l f o r the g r a n t under which p a r t of t h i s work was c a r r i e d o u t . TABLE OF CONTENTS Page Acknowledgement ^ A b s t r a c t ±± Table of C o n t e n t s i v L i s t o f I l l u s t r a t i o n s v INTRODUCTION 1 REVIEW OF PREVIOUS WORK 2 THEORETICAL CONSIDERATIONS 7 APPARATUS AND PROCEDURE 15 RESULTS OBTAINED 23 DISCUSSION OF RESULTS 35 REFERENCES 39 APPENDIX in LIST OP ILLUSTRATIONS F i g u r e Page 1 S t r e s s - S t r a i n d i a g r a m 6 2 P o t e n t i a l o f M e t a l c o v e r e d w i t h porous f i l m 12 3 S p h e r i c a l T e s t C e l l 15 k. C y l i n d r i c a l T e s t C e l l |d" l\b. D e t a i l s o f C o n s t a n t Temperature B a t h 20 5 E f f e c t o f c o l d work o f the m e t a l on change 25 i n E l e c t r o d e p o t e n t i a l 6 Change i n e l e c t r o d e p o t e n t i a l v s . s t r e s s 26 7 Change i n e l e c t r o d e p o t e n t i a l v s . s t r e s s 28 8 Change o f P o t e n t i a l w i t h time a t c o n s t a n t l o a d 29 9 Change o f P o t e n t i a l v s . l o g a r i t h m o f time 31 10 E f f e c t o f c o n c e n t r a t i o n on e l e c t r o d e p o t e n t i a l 32 11 E f f e c t o f temperature on e l e c t r o d e p o t e n t i a l 3U-12 S c a l e d Drawings o f t e s t c e l l s 4 l 13 C o n s t a n t Temperature Apparatus 1. INTRODUCTION E x a m i n a t i o n o f the d a t a o b t a i n e d f r o m v a r i o u s w o r k e r s on the e f f e c t o f s t a t i c s t r e s s on g e n e r a l c o r r o s i o n g i v e s a v e r y c o n f u s e d p i c t u r e . Some a u t h o r s have f o u n d s t a t i c s t r e s s t o i n c r e a s e c o r r o s i o n , o t h e r s have f o u n d no e f f e c t and s t i l l o t h e r s r e p o r t a decrease i n c o r r o s i o n . The e f f e c t seems s p e c i f i c b o t h f o r the m e t a l and the envi r o n m e n t . T h i s work r e p o r t s some s t u d i e s t h a t have been made on the p o t e n t i a l d i f f e r e n c e s i n d u c e d by u n i d i r e c t i o n a l t e n s i l e s t r e s s e s , i n o r d e r t o e v a l u a t e t h e i r i m p o r t a n c e i n c o r r o s i o n t h e o r y . The i n v e s t i g a t i o n has been c o n f i n e d t o v a r i o u s s i z e s and ty p e s o f copper w i r e . T h i s i n v e s t i g a t i o n r e p r e s e n t s a c o n t i n u a t i o n o f the work c a r r i e d on a t t h i s U n i v e r s i t y by M i n i a t o and McDonnell. The approach t a k e n i s r a t h e r a r a d i c a l d e p a r t u r e f r o m the p r e v i o u s a ttempts t o r e l a t e the change i n i n t e r n a l energy caused by d i s t o r t i o n o f the m e t a l t o the change i n e l e c t r o d e p o t e n t i a l . While t h i s change u n d o u b t a b l y has some e f f e c t on the e l e c t r o d e p o t e n t i a l , i t can be shown t h a t i t i s n o t the dominant f a c t o r . R e s e a r c h c a r r i e d on a t t h i s U n i v e r s i t y i n d i c a t e s t h a t s u r f a c e e f f e c t s are p a r t i c u l a r l y i m p o r t a n t i n any c o n s i d e r a t i o n o f the change o f e l e c t r o d e p o t e n t i a l w i t h a p p l i e d s t r e s s . / PREVIOUS WORK 2. In the past 60 years there has been a large number of investigations c a r r i e d out on the effect of u n l - d l r e c t i o n a l stresses on electrode p o t e n t i a l s . However, none of these have been very extensive and i n general wherever comparison has been possible there has been considerable disagreement. This d i s -agreement i s not only confined to quantity but also to the ef f e c t of various variables on the elctrode p o t e n t i a l . A major d i f f i c u l t y i n comparing re s u l t s i s the i n a b i l i t y to obtain reproducible conditions. The most frequently quoted work i s that of Walker and D i l l (1) who made a comprehensive recheck of previous work. Their main c r i t i c i s m of Andrews ( 2 ) , who had measured the poten t i a l between 20$ elongated s t e e l and ordinary s t e e l i n NaCl solution, was his method of handling the samples, and his Ignoring of time as a variable. They concluded that Hamtuechen's (3) results were doubtful since he d i d not allow s u f f i c i e n t time f o r h i s samples to reach equilibrium. Hambuechen tested s t e e l , copper, brass, zinc and wrought iron by stress i n g the samples up to the e l a s t i c l i m i t i n ferrous chloride solution. Walker and D i l l tested s t e e l samples by stressing up to the breaking point i n ferrous sulphate solutions. Their measurements were made potentiometrically with a calomel c e l l as reference electrode. The main e f f e c t they found was a considerable electronegative* Moore electronegative means a greater tendency for the metal to form irons, that the metal becomes less noble and that i t i s more anodic. (European and Nat. Bureau of Standards convention). e f f e c t above the e l a s t i c l i m i t r e a c h i n g 50 mv. a t the b r e a k i n g p o i n t . A f t e r b r e a k i n g the p o t e n t i a l r e t u r n e d toward the i n i t i a l v a l u e w i t h t i m e . Below the e l a s t i c l i m i t t h ey n o t i c e d l i t t l e o r no change i n p o t e n t i a l . S i m i l a r measurements were made on ^ - b r a s s i n s o l u t i o n s o f copper and z i n c s a l t s by M e r c i a who o b t a i n e d e l e c t r o n e g -a t i v e changes o f 0.2 mv a t the e l a s t i c l i m i t and 1.0 mv. a t the y i e l d p o i n t . These measurements were a l s o made p o t e n t i o m e t r i c -a l l y w i t h a c a l o m e l c e l l as r e f e r e n c e . A r e c e n t r e p o r t by Mears (5) emphasizes the n e g l i g i b l e e f f e c t of stress'- on the p o t e n t i a l of b r a s s . N i k i t i n (6, 7, 8) p u r s u e d the same type of i n v e s t i g a t i o n on copper, s i l v e r and i r o n , u s i n g u n s t r e s s e d samples as r e f e r e n c e e l e c t r o d e s . T e n s i l e d e f o r m a t i o n o f the m e t a l samples i n s o l u t i o n s o f t h e i r own s a l t s r e s u l t e d i n n e g a t i v e p o t e n t i a l changes o f 7 mv. maximum and l[0 mv maximum f o r copper and I r o n r e s p e c t i v e l y , and p o s i t i v e p o t e n t i a l changes of 20 mv. maximum f o r s i l v e r . These were a t t r i b u t e d t o : t e m p -e r a t u r e changes s i n c e they c o u l d be q u a l i t a t i v e l y c o r r e l a t e d w i t h the temperature c o e f f i c i e n t s o f the s i n g l e e l e c t r o d e p o t e n t i a l s . H i g h p u r i t y aluminum, w i t h c a r e f u l l y p r e p a r e d s u r f a c e s , was t e s t e d by J a c q u e t and Druet (9) i n 3% NaCl s o l u t i o n . They showed t h a t c o l d - w o r k i n g c a u s e d an e l e c t r o n e g a t i v e change o f about Ij.0 - 50 mv. Evans and Simnade (10) w h i l e s t u d y i n g c o r r o s i o n f a t i g u e i n m i l d s t e e l , r e p o r t e d on the changes I n p o t e n t i a l of s t e e l i n n e u t r a l c h l o r i d e and i n a c i d s o l u t i o n s under a l t e r n a t i n g and s t a t i c s t r e s s e s . A t any time c o m p r e s s i v e ~ s t r e s s e s gave more e l e c t r o p o g i t i v e p o t e n t i a l s , and t e n s i l e s t r e s s e s more e l e c t r o n e g a t i v e p o t e n t i a l s than when the t e s t a r e a was n o t s t r e s s e d . I n n e u t r a l s o l u t i o n s the same f i n a l p o t e n t i a l was r e a c h e d whether the t e s t a r e a was compressed, e x t e n d e d , n o t s t r e s s e d , or s u b j e c t e d t o a l t e r -n a t i n g s t r e s s . I n a c i d s o l u t i o n s g r e a t e r changes were found f o r g r e a t e r s t r e s s r a n g e s . A n nealed specimens were always more e l e c t r o p o s i t i v e than u n s t r e s s e d c o l d worked samples. There i s one r e p o r t e d attempt t o determine the e f f e c t o f c o n c e n t r a t i o n d i f f e r e n c e s o f the e l e c t r o l y t e . Gatttam and J h a (11) r e p o r t e d e l e c t r o p o s i t i v e changes f o r copper i n v a r y i n g s o l u t i o n s o f CuSO|^, w i t h more d i l u t e s o l u t i o n s r e s u l t i n g i n h i g h e r p o t e n t i a l changes. Measurement of the p o t e n t i a l d e v e l o p e d was made w i t h a suspended c o i l m i r r o r type g a l v a n o m e t e r . T e s t s were made on 22, 2l\. and 26 S.W.G copper w i r e i n N/25 and N/250 C U S O ^ s o l u t i o n s . A s i d e from the r e p o r t s on German accomplishments i n s t r e s s c o r r o s i o n s t u d i e s (12) and a b r i e f m e n t i o n i n a r e c e n t r e v i e w (13) by Harwood o f the work a t the I n s t i t u t e o f M e t a l s ( U n i v e r s i t y o f C h i c a g o ) on the e f f e c t o f s t r e s s e s on the e l e c t r o d e s o f E.M..P. c e l l s , t h e r e seems t o be l i t t l e o t h e r e x p e r i m e n t a l e v i d e n c e a v a i l a b l e ( o t h e r than the d a t a o b t a i n e d a t t h i s U n i v e r s i t y ) on the e f f e c t s o f s t r e s s on the e l e c t r o d e p o t e n t i a l s o f m e t a l s . Harwood c o n c l u d e d , from h i s r e v i e w o f the p u b l i s h e d r e s u l t s on the e f f e c t s o f s t r e s s and c o l d work on the e l e c t r o d e p o t e n t i a l s o f m e t a l s , t h a t d e s p i t e the i n c r e a s i n g 5. e x p e r i m e n t a l e v i d e n c e p o i n t i n g t o a more e l e c t r o n e g a t i v e p o t e n t i a l under the i n f l u e n c e o f t e n s i l e s t r e s s , much r e s e a r c h remains t o be done t o c l e a r up the e x i s t i n g c o n f u s i o n and t o d e f i n i t e l y e s t a b l i s h the r o l e o f s t r e s s . He su g g e s t e d t h a t s p e c i a l a t t e n t i o n be p a i d t o the methods of s u r f a c e p r e p a r a t i o n thot t o a v o i d s u r f a c e d i s t o r t i o n and f i l m f o r m a t i o n , a n d ^ c o n s i d e r a t i o n s h o u l d be g i v e n t o the p o l a r i z a t i o n b e h a v i o r o f the m e t a l system i n s p e c i f i c e n v i r onments t o c l e a r l y d i f f e r e n t i a t e any e f f e c t o f s t r e s s . The work c a r r i e d on a t t h i s U n i v e r s i t y r e p r e s e n t s the most i n t e n s i v e i n v e s t i g a t i o n as t o the n a t u r e of s t r e s s p o t e n t i a l s . M i n i a t o (II4.) hung p a i r s o f w i r e s i n s o l u t i o n s and added w e i g h t s t o one w i r e t o observe the e f f e c t o f s t r e s s on the e l e c t r o d e p o t e n t i a l . A l l measurements were made w i t h a moving c o i l g a l v a n o m e t e r . He c o n c l u d e d t h a t i n the pr e s e n c e o f some e l e c t r o l y t e s , a p o t e n t i a l d i f f e r e n c e i s d e v e l o p e d when $. s t r a i n i s p r o d u c e d by e i t h e r i n t e r n a l or a p p l i e d e x t e r n a l s t r e s s e s i n a p a r t o f the system under c o n s i d e r a t i o n . I f the c o r r o s i o n p r o d u c t of a s t r e s s p o t e n t i a l c e l l i s i n s o l u b l e , the p o t e n t i a l due t o the s t r e s s i s n e g l i b l e . He n o t e d t h a t the s t r e s s p o t e n t i a l c u r v e s f o r b o t h c o l d drawn copper and b r a s s behave e x a c t l y as t h e i r s t r e s s - s t r a i n c u r v e s do. That i s , t h e r e i s a l i n e a r r e l a t i o n s h i p up t o the e l a s t i c l i m i t , a f t e r w h i c h the c u r v e l e v e l s o f f i r r e g u l a r l y . M i n i a t o a l s o c o n c l u d e d , u s i n g v a r y i n g c o n c e n t r a t i o n s of N a C l , t h a t the s t r e s s p o t e n t i a l i s i n d e p e n d e n t o f the c o n c e n t r a t i o n of the e l e c t r o l y t e . The b e h a v i o u r o f the s t r e s s p o t e n t i a l was n o t i n v e s t i g a t e d much 6. beyond the e l a s t i c l i m i t o f the m e t a l . McDonnell (15) c o n t i n u e d M i n i a t o ' s work u s i n g s i m i l a r a p p a r a t u s , eocept t h a t he made h i s measurements u s i n g e i t h e r a p o t e n t i o m e t e r or a moving c o i l g a l v a n o m e t e r . D e s p i t e a l a r g e number of t e s t s he was u n a b l e t o r e p r o d u c e M i n i a t o ' s r e s u l t s . H i s r e s u l t s can be summarized as f o l l o w s : ( i ) the d i r e c t i o n and magnitude of the p o t e n t i a l change produced by s t r a i n i n g copper depends upon the e l e c t r o l y t e (11) s t r a i n d i d n o t a p p r e c i a b l y i n f l u e n c e the e l e c t r o d e p o t e n t i a l o f copper u n l e s s accompanied by e l o n g a t i o n ( i i i ) the magnitude of the p o t e n t i a l change produ c e d by s t r e s s i n g copper w i r e i n CuSOlj. s o l u t i o n was a l o g a r i t h m i c r e l a t i o n s h i p t o time ( i v ) p o t e n t i a l changes t h a t c o u l d be a t t r i b u t e d t o s t r e s s i n g d i d n o t o c c u r u n l e s s the copper had been exposed t o the e l e c t r o l y t e f o r a s u f f i c i e n t time f o r a f i l m t o f o r m . He c o n c l u d e d f r o m these o b s e r v a t i o n s t h a t the s t r a i n p o t e n t i a l changes are p r i m a r i l y s u r f a c e e f f e c t s and t h a t the c o n d i t i o n o f s t r a i n on the m e t a l e l e c t r o d e has l i t t l e i n f l u e n c e on the e l e c t r o d e p o t e n t i a l . THEORETICAL CONSIDERATIONS I n c o n s i d e r i n g the i n f l u e n c e of s t r e s s upon the e l e c t r o d e p o t e n t i a l o f m e t a l s , I t i s d e s i r e a b l e t o b e g i n w i t h a b r i e f d i s c u s s i o n , o f the n a t u r e of s t r e s s and a d e s c r i p t i o n of the e f f e c t s o f s t r e s s upon the i n t e r n a l s t r u c t u r e and c h a r a c t e r i s t i c s o f the m e t a l system. i S t r e s s maybe d e f i n e d as the i n t e n s i t y o f f o r c e r e a c t i o n t h a t are s e t up w i t h i n a body on the a p p l i c a t i o n o f e x t e r n a l l o a d s , or by n o n - u n i f o r m d i l a t i o n o f the body. S t r a i n i s the change i n d imensions t h a t accompanies the development of s t r e s s e s i t maybe e l a s t i c o r p l a s t i c ( i . e . i t s t i l l e x i s t s a f t e r the s t r e s s has been r e l i e v e d , l e a v i n g a permanent d e f o r m a t i o n ) . When a m e t a l i s s u b j e c t e d t o an e x t e r n a l l o a d , as by c o l d - w o r k i n g , i t i s deformed, and the d e f o r m a t i o n or f l o w b e h a v i o u r can be c h a r a c t e r i s e d by the s t r e s s - s t r a i n diagram shown i n F i g u r e 1. A l o n g the l i n e a r p o r t i o n o f the c u r v e , the s t r a i n i s p r o p o r t i o n a l t o the s t r e s s and i s e l a s t i c . However, above the e l a s t i c l i m i t ( A ) , t h i s p r o p o r t i o n a l i t y no l o n g e r e x i s t s , and p l a s t i c d e f o r m a t i o n has t a k e n p l a c e . I n complex m e c h a n i c a l p r o c e s s e s , such as d r a w i n g , r o l l i n g and e x t r u s i o n , the amount of e l a s t i c and p l a s t i c d e f o r m a t i o n t h a t o c c u r s b e f o r e f r a c t u r e depends upon the magnitude of the a p p l i e d l o a d and the s t a t e o f s t r e s s w h i c h i s p r o d u c e d . The e l a s t i c l i m i t i s n o t a w e l l d e f i n e d p h y s i c a l c o n s t a n t , and o f t e n i t i s more 8. d i f f i c u l t t o determine the e x a c t s t r e s s v a l u e f o r p l a s t i c d e f o r m a t i o n , even i n a s i m p l e t e n s i o n t e s t . I t seems c o n c e i v a b l e t h a t p l a s t i c d e f o r m a t i o n may o c c u r on a m i c r o s c o p i c s c a l e a t l o c a l i z e d s i t e s under s t r e s s e s o f v e r y s m a l l magnitude (13). Plastic Str-gih Elastic ^ Strain Total Str-alh ram-Stress Strom Curve F13 1 •^Jftien a m e t a l i s deformed i n t e r n a l changes o c c u r i n the m e t a l . I t i s o b v i o u s t h a t work i s b e i n g done on the m e t a l system, much o f wh i c h i s d i s s i p a t e d i n the f o r m o f h e a t . However, a s i g n i f i c a n t f r a c t i o n o f t h i s work, r a n g i n g f r o m 5 t o i s s t o r e d up by the m e t a l as l a t e n t energy w h i c h s e r v e s t o i n c r e a s e the i n t e r n a l energy l e v e l o f the system. I t i s t h i s i n c r e a s e i n 9. i n t e r n a l energy r e s u l t i n g f r o m the s t r a i n h a r d e n i n g p r o c e s s t o which i s a t t r i b u t e d the c h a r a c t e r i s t i c changes i n the p h y s i c a l and c h e m i c a l b e h a v i o u r o f s t r e s s e d m e t a l s as compared t o un-s t r e s s e d m e t a l s . The a r e a under the s t r e s s - s t r a i n c u r v e f o r any v a l u e o f s t r e s s and s t r a i n r e p r e s e n t s the t o t a l amount o f energy i n t r o d u c e d i n t o the m e t a l d u r i n g the d e f o r m a t i o n p r o c e s s and has been shown t o be as h i g h as 15 c a l o r i e s / g m ( 2 1 ) . For copper g w i r e under a t e n s i l e s t r e s s o f 10 dynes t h i s i s a p p r o x i m a t e l y 0.2 c a l o r i e s / g m . P l a s t i c d e f o r m a t i o n i s g e n e r a l l y accompanied by an i n c r e a s e i n s t r e n g t h p r o p e r t i e s and a decrease i n the d u c t i l i t y p r o p e r t i e s . I n a d d i t i o n to these p r o p e r t y changes, a t o m i c , c r y s t a l l o g r a p h i c and m i c r o s t r u c t u r a l a l t e r a t i o n s may o c c u r as a r e s u l t of d e f o r m a t i o n . The p r o c e s s o f p l a s t i c d e f o r m a t i o n i n v o l v e s such i n t e r n a l d i s t u r b a n c e s as s l i p , t w i n n i n g , w a r p i n g o f c r y s t a l p l a n e s , r o t a t i o n and e l o n g a t i o n o f g r a i n s , o r i e n t a t i o n e f f e c t , and a g e n e r a l breakdown of the c r y s t a l s t r u c t u r e i n t o a h i g h l y d i s o r g a n i s e d s t a t e . The e x t e n t t o which any o f these p r o c e s s e s o c c u r s i s dependent upon the magnitude o f the s t r a i n , the s t r a i n r a t e , and the temperature a t w h i c h the d e f o r m a t i o n o c c u r s ( 2 2 ) . I n o t h e r words p l a s t i c d e f o r m a t i o n i s e e s s e n t i a l l y a non-homoger&us p r o c e s s n o t o n l y f r o m a m i c r o s c o p i c p o i n t o f v i e w b u t on a m a c r o s c o p i c s c a l e as w e l l . As i n d i c a t e d e a r l i e r , p l a s t i c d e f o r m a t i o n o f m e t a l s tends t o i n c r e a s e t h e i r i n t e r n a l e n e r g y , and t h i s energy i n c r e a s e s h o u l d m a n i f e s t i t s e l f by i n c r e a s i n g the h e a t o f s o l u t i o n and 1 0 . by shifting the electrode potential in a more anodic (electronegative) direction. This is to be expected from the relationship AF r -nFE * (1) i n which s change i n free energy of the system F - faraday's constant n s no. of electrons involved E = » , e l e c t r o d e potential The changes In internal energy accompanying cold working of metals have been determined by measuring the work done during deformation and the amount of heat evolved, the difference between the two quantities being the plast ic strain energy stored in the specimen ( 2 1 ) . However, as i t i s well known for metals, suoh plast ic deformation is not a homogeneous process and very uneven distr ibution of suoh latent energy caused by cold working or similar stresses Is the aotual condition found. Clearly then* equation 1 cannot be used or modified to determine the change of electrode potential due to plast ic deformation. That a change w i l l occur due to deformation is certain but i t s mag-nitude cannot be calculated from any simple thermodynamic relationship. General Film Considerations Results obtained by previous workers and the author indicate that the effects of tensile or compressive stresses upon the oxide f i l m of the metal have a decided effect on the * this equation applies for reversible systems only and hence cannot be applied to any reaction Involving plast ic deforma-tion. 1 1 . the e l e c t r o d e p o t e n t i a l . ( 1 0 , 1 5 ) . I t h a s , f u r t h e r , been s u g g e s t e d ( l 6 ) t h a t the main e f f e c t o f t e n s i l e s t r e s s e s upon a m e t a l such as copper would be t o cause new s p l i t s and b r e a k s i n the o x i d e f i l m and t o broaden and deepen e x i s t i n g ones. A r e a c t i o n would t h e n be p o s s i b l e between the newly exposed copper and the s u r r o u n d i n g atmosphere. The change i n the p o t e n t i a l would t h e n be due t o t h i s r u p t u r e i n the f i l m and the p o t e n t i a l w i l l r e t u r n t o i t s o r i g i n a l v a l u e as the o x i d e f i l m i s b e i n g r e p a i r e d . The p o t e n t i a l o f a m e t a l as measured a g a i n s t a s o l u t i o n o r i g i n a l l y f r e e f r o m i o n s o f the m e t a l i n q u e s t i o n w i l l be s h i f t e d i n a n o b l e d i r e c t i o n I f an o x i d e f i l m be p r e s e n t . T h i s w i l l e s p e c i a l l y be the case i f the f i l m d i s p l a y s v a l v e a c t i o n , i . e . t r a n s m i t s e l e c t r o n s more e a s i l y i n one d i r e c t i o n t h a n the o t h e r . The p o t e n t i a l a t a p o i n t j u s t o u t -s i d e a porous o x i d e f i l m ( 1 9 ) maybe o b t a i n e d g r a p h i c a l l y . The c u r r e n t f l o w i n g between the f i l m (as c a t h o d e ) and t h e m e t a l exposed a t p o r e s i n the f i l m (as anode) w i l l cause the p o t e n t i a l s of f i l m and m e t a l t o approach one a n o t h e r , as i n d i c a t e d by the p o l a r i z a t i o n c h a r t C and A ( f i g u r e 2 ) . The p o t e n t i a l j u s t o u t -s i d e the f i l m w i l l be r e p r e s e n t e d by the p o i n t P on the c a t h o d i c c u r v e C, s i t u a t e d a t such a p o s i t i o n as t o g i v e a b s c i s s a i , and I n t e r c e p t i R between the two c u r v e s , where R i s the r e s i s t a n c e : f o r i R i s the r e s i d u a l E=M.P w h i c h w i l l e x a c t l y s u f f i c e t o f o r c e c u r r e n t i t h r o u g h r e s i s t a n c e R. 12. Current —* ' P o t e h t i o l o f M e t a l Covered, w t f i ° -• ' i I f the f i l m p o r o s i t y i s d e c r e a s e d , as su g g e s t e d by the bro k e n l i n e , we s h a l l I n c r e a s e R and ste e p e n the anodic p o l a r i z a t i o n c u r v e t o A, s i n c e the anodic a r e a i s d i m i n i s h e d ; s i n c e the c a t h o d i c curve w i l l hardly be a f f e c t e d , I t f o l l o w s t h a t the p o t e n t i a l w i l l r i s e t o p"*". I n g e n e r a l the s m a l l e r the p o r o s i t y of the f i l m , the h i g h e r w i l l be the p o t e n t i a l . T h i s shows c l e a r l y why, when a m e t a l c a r r y i n g an o x i d e f i l m I s immersed i n a s o l u t i o n the p o t e n t i a l w i l l t e n d t o r i s e when f i l m - r e p a i r p r e d o m i n a t e s , and t o f a l l when f i l m breakdown p r e d o m i n a t e s . T h i s i s p r o b a b l y the key t o p o t e n t i a l changes caused by s t r a i n , s i n c e s t r e s s e s would cause f i l m breakdown and would then cause a f a l l i n p o t e n t i a l . Compressive f o r c e s would decrease the p o r o s i t y o f the f i l m and hence cause an 1 3 . i n c r e a s e i n p o t e n t i a l . T h i s was shown t o be the case by-Evans and Simnade (10) G e n e r a l F i l m Theory I t has been shown, above, t h a t the p o t e n t i a l o f an e l e c t r o d e tends t o r i s e when f i l m - r e p a i r , o r growth p r e d o m i n a t e s , t h i s f i l m growth depends i n most i n s t a n c e s upon the r e l a t i v e p e r m e a b i l i t y o f the c o a t i n g t o the r e a c t a n t s . A porous c o r r o s i o n p r o d u c t f i l m i s l e s s p r o t e c t i v e t h a n one non-porous. Whether or n o t c o r r o s i o n p r o d u c t f i l m s are porous a p p a r e n t l y depends on the r e l a t i v e volume o f the c o r r o s i o n p r o d u c t compared t o the volume o f the m e t a l consumed i n f o r m i n g i t . . P i l l i n g and Bedworth (18) showed t h a t f o r o x i d a t i o n i f the r a t i o M d / ^ where: M I s the m o l e c u l a r w e i g h t o f the o x i d e D i s the d e n s i t y o f the o x i d e m I s the atomic wt. o f the m e t a l m u l t i p l i e d by the no. o f m e t a l atoms i n the o x i d e f o r m u l a d i s the m e t a l d e n s i t y . i s g r e a t e r than u n i t y , the o x i d e c o a t i n g i s p r o t e c t i v e , when l e s s than u n i t y , i t i s n o n - p r o t e c t i v e . M e t a l s a c c o r d i n g l y can be d i v i d e d i n t o two g r o u p s . 1 . One group i s composed o f the l i g h t e r m e t a l s w i t h porous o x i d e s s m a l l e r i n volume than the e q u i v a l e n t m e t a l consumed i n p r o d u c i n g the o x i d e s . These m e t a l s a t c o n s t a n t temperature o x i d i z e a t a r a t e n e a r l y c o n s t a n t w i t h t i m e . Examples are c a l c i u m (CaO and magnesium (MgO) , whi c h have r a t i o s o f M d / ^ e q u a l t o 0.61j. and 0 . 7 9 r e s p e c t i v e l y . 2. Aluminium and the h e a v i e r m e t a l s w i t h non-porous o x i d e s o f g r e a t e r volume than the e q u i v a l e n t m e t a l consumed make up,the second group. Many m e t a l s of t h i s group o x i d i z e a c c o r d i n g t o the p a r a b o l i c e q u a t i o n . Under some c o n d i t i o n s t hey o x i d i z e p r o p o r t i o n a l l y t o the l o g a r i t h m o f the t i m e . Examples are n i c k e l ( N i O ) , copper (CUgO) and chromium (C^O^) w h i c h have r a t i o s o f M d / ^ e q u a l t o 1 .60 , 1 ..71. and 2.03 r e s p e c t i v e l y (19) . There are t h r e e e q u a t i o n s (2I4.) by wh i c h common m e t a l s are known t o o x i d i z e under o r d i n a r y c o n d i t i o n s : ( i ) The r e c t i l i n e a r e q u a t i o n y=k.t + k 2 ( i i ) The l o g a r i t h m i c e q u a t i o n y = k j l o g (kjj_ t + k-5) . ( i i i ) The p a r a b o l i c e q u a t i o n y 2 = k 6 t + k ? A complete d i s c u s s i o n and d e r i v a t i o n o f the t h r e e e q u a t i o n s would be out o f p l a c e . 1 5 . APPARATUS and PROCEDURE Apparatus The appara t u s used i n the i n v e s t i g a t i o n i s q u i t e s i m p l e . B a s i c a l l y , i t c o n s i s t s o f two p a r t s , the t e s t c e l l and the d e t e c t i o n a p p a r a t u s . The t e s t c e l l can b e s t be d e s c r i b e d by r e f e r e n c e t o a diagram o u r • Figure 3 Figure 4-F i g u r e 3 i s a s k e t c h o f the f i r s t c e l l u s e d . I t c o n s i s t s o f a s p h e r i c a l g l a s s b u l b on wh i c h the f o u r s h o r t l e n g t h s o f c a p i l l a r y tubes have been a t t a c h e d . The c a p i l l a r y tubes are arra n g e d so t h a t the two t e s t w i r e s can pass t h r o u g h the c e l l as shown i n the diagram. A s m a l l f u n n e l i s a t t a c h e d t o the g l a s s b u l b t o . e n a b l e the c e l l t o be f i l l e d w i t h s o l u t i o n . A tap i s a t t a c h e d t o the bottom of the b u l b (not shown-) t o d r a i n the c e l l 1 6 . when r e q u i r e d . T h i s c e l l worked w e l l when t h e r e was no n e c e s s i t y t o r e g u l a t e the temperature o f the s o l u t i o n , however, when the e f f e c t of temperature on the change i n e l e c t r o d e p o t e n t i a l was s t u d i e d i t was n e c e s s a r y t o b u i l d a c o n s t a n t temp-e r a t u r e b a t h and i n s e r t the c e l l i n the b a t h . I t was found n e c e s s a r y t o r e - d e s i g n the c e l l f o r i n s e r t i o n i n a c o n s t a n t temp-e r a t u r e b a t h . The f i n a l c e l l s e l e c t e d was t h a t shown i n f i g u r e l i . I t has the same b a s i c c h a r a c t e r i s t i c s o f the f i r s t c e l l , the o n l y change b e i n g t h a t i n s t e a d o f the s p h e r i c a l b u l b a l o n g narrow c y l i n d e r was used. Drainage o f the c e l l was a c c o m p l i s h e d t h r o u g h the b o t t o m two c a p i l l a r i e s . S c a l e d drawings o f the two'types o f c e l l s are i n c l u d e d i n the appe n d i x . I n b o t h t y p e s o f c e l l s the t e s t w i r e s were t h r e a d e d t h r o u g h the c a p i l l a r i e s and the ends o f the c a p i l l a r i e s made l e a k - p r o o f w i t h the a i d o f 'Cenco' p a r a -r u b b e r t a p e . T h i s tape was f o u n d v e r y s a t i s f a c t o r y s i n c e i t p r e -v e n t e d the s o l u t i o n f r o m l e a k i n g f r o m the c e l l and a t the same time i t d i d n o t r e s i s t the e l o n g a t i o n o f the t e s t w i r e s . Measurements were made w i t h bare copper w i r e of s t a n d a r d s i z e 18 A.W.G and 22 A...W.G. B o t h h a r d c o l d - d r a w n copper w i r e and s o f t w i r e were t e s t e d . The m e c h a n i c a l h i s t o r y o f the w i r e i s known e x a c t l y and i s i n c l u d e d i n the ap p e n d i x . The s o l u t i o n s were made w i t h C.P. s a l t s and d o u b l y d i s -t i l l e d w a t e r . When de-oxygenated s o l u t i o n s were r e q u i r e d , n i t r o g e n was b u b b l e d t h r o u g h the s o l u t i o n f o r 15 m i n u t e s . 17. P r e p a r a t i o n o f T e s t W i r e s . The w i r e s were c u t i n t o the r e q u i r e d l e n g t h (70cms.) and s t o r e d i n a cupboard. No attempt was made t o p r o t e c t the w i r e f r o m the atmosphere. J u s t p r i o r t o use the w i r e s were c a r e -f u l l y c l e a n e d w i t h c a r b o n t e t r a c h l o r i d e and f i n a l l y w i t h m e t h y l a l c o h o l . C l e a n i n g was a c c o m p l i s h e d by w i p i n g e a ch w i r e s e v e r a l t i m e s w i t h l e n s paper soaked w i t h the s p e c i f i e d s o l v e n t s . The grease or d i r t f i l m t h a t c o a t e d the w i r e was thus removed, l e a v i n g the s u r f a c e o f the w i r e i n a s t a t e s i m i l a r t o t h a t r e s u l t i n g f r o m exposure t o the atmosphere. P r o c e d u r e . The two t e s t w i r e s were i n s e r t e d t h r o u g h the c a p i l l a r i e s of the c e l l and suspended f r o m a wooden frame. A s c a l e pan was a t t a c h e d t o the w i r e w h i c h was t o be l o a d e d w h i l e ttte l i g h t w e i g h t (500gms.) was added t o the u n l o a d e d w i r e so as t o s t r a i g h t -en the w i r e . T e n s i l e s t r e s s was a p p l i e d t o the chosen w i r e by s i m p l y l o a d i n g the s c a l e pan. G r e a t c a r e was t a k e n t o p l a c e the l o a d on w i t h o u t c a u s i n g an i m p a c t , S i n c e impact l o a d i n g would a p p l y a g r e a t e r momentary s t r e s s and c o u l d n o t be r e p r o d u c e d . I n s u l a t e d copper w i r e c o n n e c t e d the p a i r o f t e s t w i r e s t o the d e t e c t i o n a p p a r a t u s . When the chosen w i r e was l o a d e d the p o t e n t -befweert two wir-es **af » v i e o * v r e v J . T k e tmtiaf Valve o f p ' ^ n t i a l i a l v b ~ e f o r e the l o a d was added was s u b t r a c t e d f r o m the f i n a l v a l u e and the change i n e l e c t r o d e p o t e n t i a l was thus computed. Measure-ment o f the p o t e n t i a l s were made a t any d e s i r e d t i m e . I t was n e c e s s a r y t o w a i t f o r a c o n s t a n t p o t e n t i a l between the two w i r e s b e f o r e l o a d i n g , a c t u a l l y , as w i l l be shown, a s t r i c t l y c o n s t a n t 18. p o t e n t i a l cannot be a t t a i n e d . Three methods were used i n d e t e c t i n g the change i n e l e c t r o d e p o t e n t i a l : (1) P o t e n t i o m e t e r Method T h i s method r e q u i r e d two o p e r a t o r s . One o p e r a t o r k e p t the p o t e n t i o m e t e r (a p r e c i s i o n p o r t a b l e , p o t e n t i o m e t e r Leeds and Nort h r u p Model #63U-359 r e a d i n g t o V l O O o f a mv) i n b a l a n c e a t a l l t i m e s . When the l o a d was added the o p e r a t o r was abl e t o f o l l o w the p o t e n t i a l by k e e p i n g the p o t e n t i o m e t e r b a l a n c e d . (2) D.C. E l e c t r o n i c V o l t m e t e r Method The l e a d s f r o m the v o l t m e t e r / ( c i r c u i t o f B u r r , Lane and NIms 25) were a t t a c h e d t o the two w i r e s c o n s i d e r e d and t h e n the d e s i r e d l o a d added. The change i n e l e c t r o d e p o t e n t i a l was r e a d d i r e c t l y f r o m the galvanometer s c a l e . However, t h i s method though s a t i s -f a c t o r y i n p r i n c i p l e d i d n o t work too w e l l . I t was fo u n d t h a t the v o l t m e t e r tended t o d r i f t and c o n s e q u e n t l y had t o be c a l i -b r a t e d a f t e r each s e r i e s o f r e a d i n g s . T h i s v o l t m e t e r , a f t e r a s e r i e s of a l t e r a t i o n s , was d i s c a r d e d . A p p a r e n t l y the p r i n c i p l e of the. v o l t m e t e r I s c o r r e c t h u t the s e n s i t i v i t y i s too g r e a t f o r our purpose and i t would r e q u i r e c o n s i d e r a b l e s h i e l d i n g and c a r e i n o p e r a t i o n . (3) Speedomax Method A Leeds and No r t h r u p #806I|.73 Speedomax was o b t a i n e d d u r i n g the l a t t e r s t a g e s o f the i n v e s t i g a t i o n and was used wherever p o s s i b l e . The use o f the speedomax was l i m i t e d by the f a c t t h a t the range c o v e r e d by the i n s t r u m e n t was fr o m 22 t o 50 mv. 19. For the f i n a l p a r t of the i n v e s t i g a t i o n i t was n e c e s s a r y t o c o n s t r u c t a c o n s t a n t temperature b a t h w h i c h c o u l d be m a i n t a i n e d t o w i t h i n 0.1°C o f the temperature d e s i r e d . T h i s was f o r a range o f temperature f r o m 20 t o 100°C. D e t a i l s as t o the o p e r a t i o n and c o n s t r u c t i o n o f such a b a t h are u n n e c e s s a r y as s u f f i c i e n t i n f o r m a t i o n on i t can be o b t a i n e d f r o m the di a g r a m of such a b a t h w i t h the t e s t c e l l s and h e a t i n g element I n c l u d e d ( F i g u r e k B). The i n c o n s i s t e n c y and l a c k o f r e p r o d u c i b i l i t y o f the r e s u l t s r e p o r t i n p r e v i o u s work have been t o a l a r g e degree due to c o n d i t i o n s t h a t cannot be r e p r o d u c e d . I t h a s , t h e r e f o r e , been t h i s a u t h o r ' s p o l i c y t o c a r e f u l l y d e s c r i b e each p r o c e d u r e so t h a t the e x a c t p r o c e d u r e can be r e p r o d u c e d by any i n t e r e s t e d p a r t y . The p r o c e d u r e s f o l l o w e d can be c o n v e n i e n t l y d i v i d e d i n t o the f o l l o w i n g s e c t i o n s : (1) Load v s . Change i n E l e c t r o d e P o t e n t i a l The l o a d was added a t a f i x e d d e f i n i t e time i n t e r v a l (i min.) and the maximum change i n e l e c t r o d e p o t e n t i a l f o r the v a r i o u s l o a d s r e c o r d e d . A l l r u n s were made w i t h a 0 . 0 5 N CuS0[j_ s o l u t i o n and a t a room temperature o f 21°C 1 1°. Measurements o f the p o t e n t i a l between the l o a d e d and unl o a d e d w i r e s were made w i t h the p o t e n t i o m e t e r . Seven t r i a l s were made under i d e n t i c a l c o n d i t i o n s . (2) Change of E l e c t r o d e P o t e n t i a l w i t h Time. A f i x e d l o a d was added t o the s c a l e pan and the p o t e n t i a l between the two w i r e s measured a t r e g u l a r p r e - d e t e r m i n e d i n t e r v a l s . A f t e r the p o t e n t i a l had r e t u r n e d t o c l o s e t o i t s PLAN VIEW CROSS - SECTIONAL V / £ W AA All Constant Temperature Apparatus p p ' o r i g i n a l v a l u e an a d d i t i o n a l w e i g h t was added and the p o t e n t i a l a g a i n measured. I n a few c a s e s t h i s was r e p e a t e d 3 o r ly t i m e s . A l l r u n s were made w i t h a O.O^N CuSO|^ s o l u t i o n and a t a room temperature o f 21°C t 1 ° C Measurement of the p o t e n t i a l was made w i t h the p o t e n t i o m e t e r b u t l a t e r the speed-omax was used. The use o f the speedomax w i t h i t s l i m i t e d range (22 - j?0 mv) made i t n e c e s s a r y t o conduct the r u n s a t a h i g h e r temperature (85°G). Hence the l a t t e r p a r t o f the expe r i m e n t was c a r r i e d out i n the c o n s t a n t temperature b a t h . (3) E f f e c t o f C o n c e n t r a t i o n o f the S o l u t i o n i n the C e l l The e f f e c t of the c o n c e n t r a t i o n o f the e l e c t r o l y t e on the change i n e l e c t r o d e p o t e n t i a l f o r a f i x e d l o a d was d e t e r m i n e d . The e l e c t r o l y t e s t u d i e d i n t h i s case was a s o l u t i o n o f CuSCj^, the c o n c e n t r a t i o n o f w h i c h r a n g e d f r o m 0.5>N t o O.OOO0N. F i x e d l o a d s were added t o the s c a l e pan and the maximum change i n e l e c t r o d e p o t e n t i a l n o t e d . A f t e r the passage o f h a l f a minute an a d d i t i o n a l w e i g h t was added and the maximum e l e c t r o d e p o t e n t i a l change n o t e d a g a i n . T h i s p r o c e d u r e was r e p e a t e d s e v e r a l t i m e s ; Measurements were made w i t h a p o t e n t i o m e t e r . E f f e c t o f D i f f e r e n t E l e c t r o l y t e s . The p r o c e d u r e f o l l o w e d i n 3 was r e p e a t e d , b u t i n s t e a d o f v a r y i n g the c o n c e n t r a t i o n o f CuSOj^, d i f f e r e n t e l e c t r o l y t e s were us e d . The f o l l o w i n g were the e l e c t r o l y t e s u sed: O.O^N CuSO^ O.O^N MgSO^ 0.G5N C u C l 2 (5) E f f e c t o f Temperature The c e l l s i n the c o n s t a n t temperature b a t h were f i l l e d w i t h 2 2 . solution one ha l f hour before being loaded. This was necessary to enable the solution to attain the temperature of the bath. This temperature ranged from 25° to 85°C. The selected wire was then loaded with the f i x e d weight, 8kgm, and the change i n potential detected by the potentiometer. To obtain the most probable r e s u l t six t r i a l s were made at each selected temperature. The speedomax was also used as a further check of some of the r e s u l t s Obtained. (6) Change of Potential with Time at Zero Load The v a r i a t i o n of pot e n t i a l with time with zero load was investigated at a constant temperature of 21 '+ 1 ° C This was accomplished by suspending the wires i n a 0.05N CuSOj^ solution and taking readings of po t e n t i a l between the two wires at various i n t e r v a l s over a 21+. hour period. Nine pairs of wires were tested. No attempt was made to determine the e f f e c t of the length of wire exposed to the solut i o n . McDonnell (15) reported that this e f f e c t was. n e g l i g i b l e . In every case the length of wire exposed was the maximum allowed by the c e l l s used i . e . V~> cms for the spherical c e l l and 36 cms. for the c y l i n d r i c a l c e l l . RESULTS OBTAINED 2 3 . The r e s u l t s obtained i n some cases duplicated the r e s u l t s obtained by McDonnell(15) and other workers, but this i s desireable since the reports on previous work have been highly c o n f l i c t i n g . The r e s u l t s reported here are e a s i l y reproducible. A l l r e s u l t s were checked at l e a s t 3 times and i n some cases as many as 10 times and i n not a single case were there any con-f l i c t i n g r e s u l t s obtained. Checking was accomplished by repeating the experiment under exactly similar conditions with new wires and a f r e s h solution. 1. In a l l cases examined the sof t copper wires gave greater changes In p o t e n t i a l than the cold-drawn copper wires. In most cases I t was not possible to measure the change i n electrode p o t e n t i a l of cold-drawn copper wire using the same loading system as that used f o r the sof t copper id re.. Any change i n p o t e n t i a l detected f o r the hard copper wire was exceedingly small (0.2 mv.) and might e a s i l y have been due to p o l a r i z a t i o n e f f e c t s . However, i f i t had been possible to s t r a i n the wire permanently a greater change i n electrode p o t e n t i a l would have occurred. A greater stress was found necessary to produce a p a r t i c u l a r change of p o t e n t i a l at the second stressing than was required at the f i r s t stressing (Figure 5 . ) This n a t u r a l l y follows from the f a c t that p l a s t i c s t r a i n decreases the d u c t i l i t y of the metal and since i t can be shown (Figures 6 , 7) that the 2k. p o t e n t i a l e f f e c t s are d i r e c t l y dependent on the amount of e l o n g a t i o n . 2. No s i g n i f i c a n t d i f f e r e n c e s was f o u n d f o r de-oxygenated s o l u t i o n s as opposed t o o r d i n a r y s o l u t i o n s c o n t a i n i n g d i s s o l v e d oxygen and n i t r o g e n . However, the method o f de-oxygen-a t i o n might have been a t f a u l t , s i n c e the c o n c e n t r a t i o n o f oxygen i n the s o l u t i o n g e n e r a l l y e x e r t s some i n f l u e n c e on the r a t e o f f i l m f o r m a t i o n . The e f f e c t o f a c o n t r o l l e d atmosphere (e.g. N 2) was a l s o f o u n d n e g l i g i b l e i n the p r o c e d u r e f o l l o w e d . 3. F o r a l l t e s t s on copper i n CuSOj^ s o l u t i o n , e l e c t r o - n e g a t i v e p o t e n t i a l changes were o b t a i n e d f o r the a p p l i c a t i o n o f t e n s i l e s t r e s s e s . F o r a s e r i e s o f seven p a i r s of w i r e s (#18 A.W.G s o f t copper) i n 0 .05N C U S O J ^ s o l u t i o n , the e f f e c t o f i n c r e a s i n g s t r e s s was n o t e d by the a d d i t i o n o f c o n s t a n t i n c r e m e n t s of l o a d a t c o n s t a n t time i n t e r v a l s , and r e c o r d i n g the maximum change i n p o t e n t i a l f o r e a c h i n c r e m e n t o f l o a d . A l i n e a r p l o t o f change i n e l e c t r o d e p o t e n t i a l i n m i l l i v o l t s between s t r e s s e d and un-2 s t r e s s e d w i r e s a g a i n s t s t r e s s i n kgm/cm i s g i v e n i n F i g u r e 7. Each curve has two c r i t i c a l p o i n t s , and the s t r e s s v a l u e s c o r r e s p o n d i n g t o the two p o i n t s are r e m a r k a b l y c o n s t a n t f o r a l l seven d e t e r m i n a t i o n s . The range o f r e p r o d u c i b i l i t y of r e s u l t s i n such d e t e r m i n a t i o n s i s a l s o e v i d e n t . The c r i t i c a l p o i n t s o b t a i n e d are a t a p p r o x i m a t e l y 6 x 1CH kgm/cm and 8 x 10^ kgm/cm . Beyond the second c r i t i c a l p o i n t t h e r e i s l i t t l e e v i d e n c e of f u r t h e r p o t e n t i a l change. A s i m i l a r p l o t i s made i n F i g u r e 6 comparing the r e s u l t s o b t a i n e d i n t h i s i n v e s t i g a t i o n w i t h those EFFECT OF COLD WORK OF THE METAL ELECTRODE POTENTIAL. UJ 2 < X o UJ o CL UJ > o o ' or h-o UJ 1 . UJ 1 21 SWG annealed Cu ' 2 5 C U S 0 4 2 Reloadinq of (I) afferunloa dinq J L J l_ 4 8 10 LOAD K 6 M / C M * X I 0 " 2 3 U r e Fig ure 6 27. obtained by McDonnellfor d i f f e r e n t diameter copper wi r e s , I t can be seen that w i t h a smaller diameter wire the f i r s t c r i t i c a l p o i n t occurs at.a l o a d value l e s s than that of the l a r g e r diameter w i r e . The maximum p o t e n t i a l change w i t h 18 A.W.G s o f t copper wire i n 0 . 0 5 N CuSO]^ s o l u t i o n i s approximately 5.75 mv., while that f o r 21 S.W.G. annealed copper In O.Oi^ CuSO^ i s about 1+.75 mv. Part of t h i s d i f f e r e n c e i s due, no doubt, to the d i f f e r e n c e i n concent r a t i o n of the s o l u t i o n . ij.. A l l p o t e n t i a l changes produced by a p p l i c a t i o n of t e n s i l e s t r e s s tended to drop to zero w i t h time, and removal of the a p p l i e d s t r e s s caused l i t t l e or no change i n the p o t e n t i a l . I t should be noted that the p o t e n t i a l change never d i d reach zero but seemed to l e v e l o f f at a value s l i g h t l y above zero. For copper wires i n CuSO^ s o l u t i o n the p o t e n t i a l time curves were l o g a r i t h m i c i n ch a r a c t e r . Combining the r e s u l t s of t h i s work w i t h McDonnell's work (15) i t can be seen that the slope of p o t e n t i a l change vs l o g a r i t h m of time p l o t i s dependent on the s i z e of wire used i n c r e a s i n g ( i n negative value) f o r l a r g e r wire s i x e s . T y p i c a l r e s u l t s are given i n Figures 8 and 9« An important observation was made i n tha t an; i n d u c t i o n p e r i o d f o r the wire i n the e l e c t r o l y t e i s apparently necessary before any p o t e n t i a l change i s p o s s i b l e w i t h the a p p l i c a t i o n of s t r e s s . The l e n g t h of the i n d u c t i o n p e r i o d , provided i t was of s u f f i c i e n t l e n g t h (15 minutes), d i d not a f f e c t the magnitude of the change In p o t e n t i a l . (Table I ) > 8 0 0 10 2 0 30 40 T I M E I N M I N U T E S F i g u r e 8 (Table Jl) o 3 0 . 5. By varying the concentration of the CuS0[j_ solution from 0..SN to 0.0005.N i t was found that both the magni-tude and rate of change of the electrode potential caused by stress tended to increase. The change from 0.005N to 0.0005N was significant hut small, and introduces the poss ib i l i ty of a l imit ing concentration for such an effect. The results of concentration versus electrode potential for two different loads are plotted in Figure 10. Three t r i a l s were made at each concentration and the average of the three values obtained plotted to provide the graph. 6. Various electrolytes have been found to give considerably different potential-time curves. The sense, the magnitude and the rate of change of the potential caused by stress application a l l vary with the electrolyte . The general observations may be summarized as follows: (i) 0.05N CuSO^ electronegative change about i f mv. maximum. ( i i ) 0 . 0 5 N MgS0^ _ electronegative change about 11 mv. maximum, ( i i i ) 0 . 0 5 N GuCl 2 electropositive change about 5«5 maximum, (iv) 0 . 7 N NaCl electronegative change about 11 .5 mv. maximum, (v) 1.0N Na2S0]^ electronegative change about 11 mv. maximum. Results (IV) and (v) are those obtained by McDonnell (15) • THE EFFECT OF CONCN OF ELEC ON STRESS POTENTIAL OOI o oa o o 18 B8S SOFT C O P P E R CJS0 4 SOLN 0 0 0 1 LOAD 2 LOAD 992 KGM/CM 86 8 KGM/CM^ E L E C T R O N E G A T I V E C H A N f r E IN P O T E N T I A L Fiqure 10 (Table. JL) 33.. R e s u l t s ( i ) , ( i i ) and ( i i i ) are the average of 3 t r i a l s w i t h each type of e l e c t r o l y t e . 7. The e f f e c t of temperature on e l e c t r o d e p o t e n t i a l changes was a l s o i n v e s t i g a t e d . Using ^ 1 8 A.W.G. s o f t copper wire i n 0.05N CuSOj^ s o l u t i o n , i t was found t h a t f o r a constant 2 s t r e s s a p p l i c a t i o n of 992 kgms per cm the maximum p o t e n t i a l which i s about ij. mv at 2 5 QC r i s e s to over 30 mv. at 8 5°C. With the same l o a d and u s i n g a s o l u t i o n of 0.005N CuSO]^, the p o t e n t i a l change r i s e s to w e l l over 50 mv. at 85°C. The r e l a t i o n s h i p between the l o g a r i t h m of the e l e c t r o d e p o t e n t i a l change and the r e c i p r o c a l of the absolute temperature i s l i n e a r . S i x re a d i n g s at each temperature were made and the average of the readings were used i n the p l o t o b t a i n e d i n F i g u r e 1 1 . I t w i l l be n o t i c e d t h a t the l a s t two p o i n t s i . e . at a temperature of 25°C and 32°C do n o t f a l l e x a c t l y on-the s t r a i g h t l i n e through the other seven p o i n t s . The slope of the l i n e d l o g (BP) i s equal to 1 . 5 2 x 1QJ, d (1/T) ~ and the i n t e r c e p t of the l i n e i s equal to $ From these two va l u e s an equation r e l a t i n g the change i n e l e c t r o d e p o t e n t i a l w i t h temperature can be obt a i n e d : l o g (EP) = 1 . 5 2 x 1 0 3 l / T + 5.71}-. , This equation i s , o b v i o u s l y , c o n f i n e d to the c o n d i t i o n s under which the i n v e s t i g a t i o n was c a r r i e d out, i . e . copper wire i n 0 . 0 5 N CuSO^ s o l u t i o n . EFFECT OF TEMPERATURE ON CHANG-E OF ELECTRODE POTENTIAL AT A FIXED LOAD Figure II ( T o t f e ^ 3 5 . DISCUSSION OP RESULTS The general r e s u l t s i n d i c a t e that i n i t i a l l y s t r e s s causes e l e c t r o n e g a t i v e change i n p o t e n t i a l , a change suggestive of increase c o r r o s i v i t y . Prom time p o t e n t i a l curves however, i t i s found that such e l e c t r o n e g a t i v e changes decrease r a p i d l y w i t h time, i . e . the s t r e s s e d metal i s becoming more p a s s i v e . This can be i n t e r p r e t e d simply as the exposure of new metal surface due to s t r e s s , and the gradual formation of an impervious surface f i l m due to c o r r o s i o n products formed from the metal surface and the surrounding medium. The n e c e s s i t y of an i n d u c t i o n p e r i o d i n the e l e c t r o l y t e ; the v a r i a t i o n of p o t e n t i a l change w i t h increased l o a d i n g , w i t h c o n c e n t r a t i o n changes, w i t h v a r i a t i o n i n the e l e c t r o -l y t e and w i t h temperature, a l l i n d i c a t e that breaking and making of a surface f i l m l a y e r I s the dominant f a c t o r i n v o l v e d . The formation of many oxide l a y e r s i s l o g a r i t h m i c w i t h time (2l\.) and the time p o t e n t i a l curves obtained are the r e f o r e to be expected. I t i s u s u a l l y considered that a l a y e r of cuprous oxide i s present on copper i n aqueous s o l u t i o n s . This tends to be rep l a c e d by one of cuprous c h l o r i d e i n c h l o r i d e - i o n s o l u t i o n s . The d i f f e r e n c e i n p o t e n t i a l changes observed w i t h CuSO^ and w i t h C u C l 2 i s therefore understandable. The con c e n t r a t i o n changes w i l l i n turn a f f e c t not only the r a t e of formation of an oxide l a y e r at newly exposed p o r t i o n s , but w i l l a l s o a f f e c t the p o t e n t i a l . I t i s considered a l s o that t e n s i l e s t r e s s i n g w i t h i t s 36. exposure of fre s h metal and the resultant formation of surface layers w i l l give a new balance to the anodic and cathodic areas equilibrium on the surface of the cppper. This i n turn affects the degree of l o c a l p o l a r i z a t i o n and hence the ov e r a l l p o t e n t i a l e f f e c t . The r e s u l t s obtained for the poten t i a l - load curves indicate that the pot e n t i a l change produced i s proportional to the new surface area exposed per unit lengJfah of wire. The curves, however, indicate a l i m i t i n g value f o r "the p o t e n t i a l . Thfe l i m i t as indicated by the graphs (6, 7) i s deceptive since i t indicates that above a c e r t a i n load no increase In p o t e n t i a l change i s possible. That this was not the case was demonstrated by adding a large load (5 kgm) to the c r i t i c a l load obtained. n The wire, under th i s load, elongated u n t i l rupture and the pot e n t i a l increased i n a negative d i r e c t i o n u n t i l the wire ruptured. Obviously then, the l i m i t i s that value attained when the wire breaks i . e . when no fre s h metal i s exposed. The curve obtained with i t s decreasing p o t e n t i a l change per unit of load can be ex-plained by the decrease i n d u c t i l i t y of worked metals. Clearly then, the physical nature of the metal must be known and i t s s t r e s s - s t r a i n c h a r a c t e r i s t i c s understood before any consideration of the ef f e c t s on s t r a i n on electrode potentials can be studied. Soft, or annealed copper s t r e s s - s t r a i n curve has no l i n e a r portion, hence a l i n e a r r e l a t i o n s h i p between pote n t i a l and load i s not to be expected and i s , indeed, not obtained. The e f f e c t of temperature on the magnitude of the 37. p o t e n t i a l change v e r s u s the r e c i p r o c a l o f the a b s o l u t e temp-e r a t u r e y i e l d s a s t r a i g h t l i n e . T h i s temperature dependence i s u s u a l l y g i v e n by an e q u a t i o n o f the A r r h e n i u s type i n v o l v i n g an energy o f a c t i v a t i o n . T h i s i n d i c a t e s t h a t the change i n e l e c t r o d e p o t e n t i a l due t o s t r e s s c o r r e s p o n d s t o a r a t e r e a c t i o n and t h a t t h i s change i n p o t e n t i a l i s p r o p o r t i o n a l t o the r a t e o f fUt A Tt»e e x a c t r e l a t i o n s h i p between r a t e and e l e c t r o d e p o t e n t i a l change i s n o t known. An e q u a t i o n showing the temperature dependence o f s t r a i n p o t e n t i a l s f o r s o f t copper i n 0.05N C U S O[L s o l u t i o n has been o b t a i n e d . I t i s e x p e c t e d t h a t f o r a s e r i e s o f d i f f e r e n t c o n c e n t r a t i o n s a whole f a m i l y o f such e q u a t i o n s c a n be o b t a i n e d . L i t t l e use c a n be made o f them, however, u n t i l a r e l a t i o n s h i p between r a t e and e l e c t r o d e p o t e n t i a l change i s e s t a b l i s h e d . I t has been shown t h a t when copper s u f f e r s p l a s t i c d e f o r m a t i o n t h e r e i s a l a r g e change i n p o t e n t i a l i n the e l e c t r o -n e g a t i v e d i r e c t i o n , and t h a t t h i s p o t e n t i a l change d e c r e a s e s i n magnitude f i r s t r a p i d l y and t h e n g r a d u a l l y s l o w e r f i n a l l y a p p r o a c h i n g a s s y m t o t i c a l l y some v a l u e a l i t t l e g r e a t e r than the i n i t i a l v a l u e b e f o r e s t r a i n ( F i g u r e 8 ) . T h i s v a l u e never approaches the i n i t i a l v a l u e . C l e a r l y t h e n , t h i s i n d i c a t e s two d i f f e r e n t e f f e c t s c a u s e d by p l a s t i c s t r a i n . The f i r s t e f f e c t t h a t o f the r u p t u r e o f the s u r f a c e f i l m i s g r a d u a l l y o f f s e t by the r e p a i r t o the f i l m , hence the p o t e n t i a l change caused by t h i s e f f e c t w i l l g r a d u a l l y r e t u r n t o z e r o as the s u r f a c e f i l m i s r e p a i r e d . The p o t e n t i a l change, i t has been shown, does n o t r e t u r n t o z e r o , t h i s can be e x p l a i n e d by the f a c t t h a t the m e t a l 38. system has been p e r m a n e n t l y a l t e r e d and has had I t s I n t e r n a l energy i n c r e a s e d g i v i n g r i s e t o an i n c r e a s e i n p o t e n t i a l o f the m e t a l . The l i m i t a t i o n s t h a t have e x i s t e d i n t h i s work may be summarized as f o l l o w s : (1) The p o t e n t ! o m e t r i e method o f measurement a l l o w s a p o s s i b l e change i n the p o t e n t i a l b e i n g measured b e f o r e a b a l a n c e i s o b t a i n e d . There i s always the i m p o s i t i o n o f a s l i g h t m e a s u r i n g c u r r e n t i n such a method, and the p o l a r i z a t i o n e f f e c t s t h e r e b y c a used w i l l d e f i n i t e l y have an i m p o r t a n t e f f e c t . (2) The l a c k o f homogeneity i n the m e t a l i t s e l f as w e l l as i n i t s s u r f a c e o x i d e l a y e r remove the p o s s i b i l i t y o f c o m p l e t e l y r e v e r s i b l e e f f e c t s and reduce the p o s s i b l e r e p r o d u c i b i l i t y . Improvements L i t t l e can be done about the second l i m i t a t i o n , how-ever the f i r s t l i m i t a t i o n can e a s i l y be r e c t i f i e d by e i t h e r a q u i c k response e l e c t r o n i c v o l t m e t e r or a.speedomax. A speedomax was u sed i n the l a t e r p a r t of t h i s i n v e s t i g a t i o n and was f o u n d i d e a l f o r the p u r p o s e . U n f o r t u n a t e l y , the range c o v e r e d was n o t s a t i s f a c t o r y b u t a new s l i d e w i r e c o u l d be o b t a i n e d w h i c h would enable the i n s t r u m e n t t o c o v e r the d e s i r e d range . 3 9 . BIBLIOGRAPHY .1. Walker W., and D i l l C , Trans. Am. Electrochem. S o c , 11, 153 (1907). 2. Andrews T., Proc. I n s t . C i v i l Eng. (Br.) 11,8. 356, ( l 8 9 i i ) . 3 . Hambuechen C , B u l l . Univ. W i s e , Eng. Se r i e s 2, 8, 235 (1900) i i . Mercia P-. D., Met. Chem. Eng., l£, 321, (191.6). 5 . Mears R. B., Metal Progress, 1L8, 105 . 6 . N i k i t i n L. V., Compt. rend. acad. s c i . U. S. S. R, 17_, 107 ( 1 9 3 7 ) . , 7. N i k i t i n L. V., J . Gen. Chem. (U. S. S. R), % 7 9 V ( 1 9 3 9 ) . 8 . N i k i t i n L. V., J . Gen. Chem (U, S . S . R ) , 11, II4.6 O.9I4L) 9 . Druet Y. and Jacquet P. A., Metaux et Cor r o s i o n , 22, 139 (191+-7) 10. Evans U. R. and Simnade M. T., Proc. Roy. Soc. (London), 188A. 3 7 2 , 1 9 4 6 . 11 . Gautam L. R. and Jha J . B. Proc. Indian Acad. S c i . , 18A, 350 (1953) 12. Nangle C. A. A i r M a t e r i a l Command Tech. Report FT - R 1131 - ND (19)4-7). 13* Harwood J . J . Cor r o s i o n , 6, no 8 , 2ij-9 (1950) 11L. Miniato 0 . K. Measurement of Str e s s P o t e n t i a l s . M. A. Sc. Thesis i n Chem. Eng., Univ. o f B . C. (l9i|-7). 15. McDonnell B. E f f e c t of St r e s s on E l e c t r o l y t i c S o l u t i o n P o t e n t i a l . M. A. Sc. Thesis i n 6hem. Eng., Univ. of B. G. (19IL8) 4-0. 16. Shemilt L. W. The E f f e c t of U n i - d i r e c t i o n a l Stresses on Elec t r o d e P o t e n t i a l s . Paper presented at Symposium on E l e c t r o c h e m i s t r y and Co r r o s i o n . Ottawa, Nov. 1950. 17. Bannister L. C. and Evans U. R. J . Chem Soc. l4&4* (1930) 18. P i l l i n g N. B. and Bedworth R. E. J . I n s t . Metals 2£, 534* (1923) 19. Evans. U. R. M e t a l l i c C o r r o s i o n , P a s s i v i t y and P r o t e c t i o n . Edward Arnold and Co. London 1937 pg i S S X X X K 2 0 . Evans U. R. M e t a l l i c C o r r o s i o n , P a s s i v i t y and P r o t e c t i o n Edward Arnold and Co. London 194-8 Pg 122. 21 . Taylor G. I . and Quinney H. Proc. Roy. Soc. (London) 143A, 307 (1934). 22. Bohnenblush H. P. and Dewez P., Trans. A. S. M. E. 70, 222 (1948). 23. Peterson R. E., Trans. A. S. M. E. A.P.M. 55-19 . (1933). 24. Evans U. R. Trans Am. Electrochem. Soc. 83_, 335 (1943) 25 Burr H. S., Lane C. T., and Nims L. P. Yale J . B i o l , and Med. % 6£, 1936) . Cor\startt TewpenatMre. Apparatus F i g u r e . 13 TABLE I Potential vs Stress 18 B. and S. Soft Cu wire Soln'. N/20 CuSO^ Load Kgm 2 3 4 5 6 7 9 11 18 B. and S. Soft Cu wire Soln. N/20 CuSO^ Load Kgm 3 I 7 8 9 11 Kgm/cm2 372 620 m 992 1120 1360 Potent. D i f f mv +0.45 +0.24 -O.70 -3.61 -4 . 5 8 -4 . 3 2 • -4 -37 1ft B. and S, 'a«ft Cu wir~ s » m N/20 CuSO), Load Kgm 2 ! 7 9 11 Kgm/cm2 248 496 620 m 1120 . 1360 Potent. D i f f . mv 1-47 l.lp. I . 3 2 0 . 3 1 - 1 . 1 7 - 2 . 1 6 - 2 . 1 6 .R R : flnd S.. ™ w i r e S o l i i N/20 CuSO), Load Kgm h 6 . 3 6 . 8 8 . 3 Potent. D i f f . mv ^.0.96 - 1 . 0 1 - 1 . 2 2 - 1 . 7 7 - 2 . 6 7 -3.00' -3.49 (A) ~A E mv 0 . 0 6 0.27 1.21 4.II 5.09 4 . 8 3 4 . 8 8 -A E mv 0.02 0.08 0.17 1.80 2 .66 3 . 6 5 3 . 6 5 -A E mv 0 . 0 5 0 . 1 0 0 . 3 1 0 . 8 6 .1.77 2 . 1 0 2 . 5 8 (B) (C) (D) 18 B. and S. Sof t Cu wire Soln... N/20 CuSO^• Load Kgm 3 k-5 5-5 6.1 6.3 7.3 8.3 9.3 10.3 Kgm/cm 372 559 683 .757 781 905 1030 1150 1280 Load Kgm 2.0 3.0 3.5 . I L . O k-5 5.1 6.5 7.5 Kgm/cm* 2IL8 , 372 k 558 633 806 930 . Load Kgm . 3.0 3.5 IL . O ' k-5 5.1 6.5 7.5 8.5 9.5 13.5 Kgm/cm 372 $ 558 633 806 930 1053 1180 1670 Potent. D i f f . mv -0.11 -0.26 - O . k k -1.51+--2.10 - i i . 0 7 -4.71 . -4 .63 -1L .89 18 B. and S. Sof t Cu wire S o l n . N/20 CuS0| r Potent. D i f f mv - 0.03 - O . O I L - 0.07 - 0 . 2J4. - - 0 4 7 - 0 . 8 7 - 2.k5 -2.82 - 4 E mv 0.11 0.26 O.kiL I . 54 2.10 4.07 4.71 I I . 63 4 .89 - 4 E mv 0 .03 . O.OI4. 0.07 O..2I4. 0 4 7 0.87 2.L5 .2.82 18 B. and S. S o f t Cu wire Soln. N/20 CuSO^. Potent. D i f f . mv - 0.08 •* 0.12 - 0.30 - 0 . 7 8 - 1.58 - 3 4 7 • -5.51* - 5 . 9 5 - 6.J1I - 7.83 - 4 . E mv 0.08 0.12 0.30 0.78 1.58 3 4 7 6 .Iii 7.83 TABLE I I Potential vs Time at Various 4 5 , Fixed Loads 18 B. and S. Soft Cu Wire N/20 CuSO), . Time Load . - ' 2 Potent. Di f f . > ^ E mlns. Kgm Kgm/cm -mv. mv. o o 0.33 0.00 6 0 0.33 0.00 13 6 744 -1 .42 1.75 14 -1 .07 1.40 15 - 0 . 7 9 1.12 16 - 0 . 6 6 0.99 17 - 0 . 5 3 0.86 -0.4£ 18 ' - 0 . 4 8 0.81 19'; - 0 . 4 1 . 0 . 7 4 21 22 o h - 0 . 2 3 0/56 25 26 28 40 50 Q 992 - 2 . 5 2 2.85 51 - 2 . 2 9 2.62 52 - 2.00 2.33 53 -1.75 2:08 54 - 1 . 5 7 1.90 55 - 1 . 4 4 1.77 56 • - .1 .33 1.66 57 10 1240 ~ 2 . 5 3 2.86 58 - 2 . 0 0 2.33 -O.36 O.69 - 0 . 3 2 0.65 - 0 . 2 9 0.62 - 0 . 2 5 0.58 O .23 .- 0 . 2 1 0 .54 - 0 . 1 9 0.52 - 0 . 1 4 0.47 0.00 0.33 46 18 B. and S. Cu w i r e S o l n N/20 CuSOj^ (A) Time Load J : / : > ... 1 . l;LS?.- - A E mins Kgm Kgm/cm2 Potent. D i f f . mv mv 0 0 0 +0.67 0.00 +0.68 . 0.00 6 7.-44 • +0.18 0.50 lh 0.29 0.38 17 0.35 0.32 18 O.38 0.30 19 O.38 0.30 20 0.38 .0.29 21 0.39 0.85 2 2 0.4o 0 . 2 7 23 0 .4 l 0.26 36 8 992 -2.59 3.26 37 -2.17 2.84 •38 -1.83 2.51 39 -1.64 2.31 40 -1.44 2.12 41 -1.31 1.98 42 -1.19 1.87 4L -1.02 1.70 4g 9 1120 -2.36 3.03 ll -2.05 2.72 48 -1.77 2.44-4Q - 1 . 5 6 2 . 2 4 |6 -1.42 2.10 5 2 10 1240 -2.43 3.11 ^ -1.85 2.53' f t -1.63 2.30 St - " l - ^ : 2.12 5? -1-31 1.98 - 1 . 2 1 1 . 8 8 - l . l l 1 . 7 8 - 1 . 0 2 1 . 7 0 57 58 60 -0.95 1.62 65 -0.67 1.34 70 -O.46 1.14 18 B. and S. S o f t Cu wire S o l n . N/20 CuSO^ (B) Potent. D i f f — AE Kgm/cm2 mv mv 0 1.92 0 .00 Ikk' Time Load mins Kgm 10 0 10 6 11 12 i 16 ^7 18 20 21 22 23 25 27 29 38 i t f l 66 8 67 68 69 70 72 992 48 18 B. and S. S o f t Cu w i r e S o l n . N/20 C U S O ^ Time Load P o t e n t . D i f f -A.E mins Kgm Kgm/cm2 mv mv 0 0 0 0 .29 0 .00 10 1240 - 3 . 3 2 3 11 -1.5: - 1 . 4 4 496 0.11 0.18 5 620 - 0 . 2 7 0,55 - 0 . 1 8 0.47 - 0 . 0 8 0 .36 - 0 . 0 5 0 . 3 4 6 744- - 2 . 0 0 2 .2" - 1 . 5 ? 1.8 - I . 2 4 1.53 - 1 . 0 0 1.29 - O . 7 9 1.08 -0 .65 0 . 9 k -o .£6 0.84 - 0 . 4 7 0 .76 - 0 . 4 0 0 .69 0^.34 0 .63 8 992 -3.60 3 . 8 " - 3 4 9 3.4' - 2 . 6 9 2.98 - 2 . 4 l 2.70 - 2 . 2 0 2.49 - 2 . 0 1 2.30 - 1 . 8 4 2.13 -1.71 2 .09 5 1 .84 1.72 .61 3.31 3.08 - 2 . 6 3 2.92 -2.44 - 3 . 0 2 3 .31 - 2 . 7 9 3 .08 - - • ^ 2.73 1360 ^4.10 4 .40 - 3 . 3 8 3 ,67 18 B. and S. Soft Cu wire Soln. N/20 CuSO), Time Load 0 Potent. Dif f mins Kgm Kgm/cm2 mv 0 0 - . 13 k 5-96 - .15 - .12 5 620 -.hi - . 3 4 - . 3 2 6 71*4 -2.57 - 2 . 1 9 -1 .76 -1.53 -1 .38 -1 .26 -1.17 - 1 . 0 9 -O.98 8 992 - 3 . 2 0 - 3 . 0 0 -2.1+5 ^2.27 -2.13 - 2 . 0 1 t--1 .78 -1 .72 11 1360 ~2.61L - 2 . t o -2 .111 - 1 . 9 9 h9 50 TABLE I I I C o n c e n t r a t i o n vs E l e c t r o d e P o t e n t i a l 18 B. and S. S o f t Cu wire SolnO-<?5CuS0), 0.05 N CuSO)j Time Load mine Kgm 0 0 e 3 2 3 2.15 4 4.15 4 4.30 6 A 6.45 u 7 8.45 7 9.00 8 9.45- . 8 0 .5 N CuSOlj. Time Load mins Kgm 0 . 9 0 3 2 3 2.l£ 4 4.15 4 4.30 6 6.30 6 6.45 7 8.45 7 9.00 8 9-45 8 - 4 E mv Kgm/cm2 Run #1 Run #2 'Run #3 0 372 0.12 0.11 - 0 . 0 7 372 0.12 0.06 0.05 496 0.12 0.10 0 . 0 4 496 0.25 0.09 0.03 744 0.37 1.49 . 0.86 7ii4 0 0.91 0.45 0.12 o . l l .12 0.06 0.12 0.10 0.25 0.09 0.37 1.49 0 0.Q1 3.H 2.61 1.57 1.71 2.61 • 2.31 2.50 2.81 -A E mv 868 .11 .6l 1.98 868 . 7 .  1.03 992 . 1  . 1 2.18 992 - .50 . 1 1.54 Kgm/cm2 Run #1 Run #2 Run #3 0 372 0.11 0.03 372 0.02 . 0.06 496 0.02 . 0.03 1I96 0.01 0.03 744 0.32 0.17 7IA 0.18 0.14 868 0.60 0.58 868 0.33 0.35 992 0:;70 0.75 992 0.49 0.59 51 0 . 0 0 5 N.CuS0)[. Time Load mins Kgm 0 0 0 3 2 3 2.15 i M S I 5-30 6.3O 6 6 6 . f o 7 8.45 7 9.00 8 9 4 5 8 -•^E my Kgm/cm2 Rim #1 Run #2 Run #3 0 372 0 . 0 4 0.06 0.05 372 0 . 0 4 0 .05 J4.96 0.0Q O.Oii L96 O.kb 0 .0k 0.66 7hk 2.66 l i .16 7lijl 1.69 2.16 O . l i i 868 8.51 7 4 9 2.91 868 I 4 . . 3 8 3 . 81+ 0 .68 992 10.03 7-3U- 3131 992 II.OIL 5 . l 6 2.19 0 .0005 N CuS0) f Time Load . , ^. mins Kgm Kgm/cm2 - Run #1 Run #2 Run #3. Run #ii Ron**? 0 " ' 3 372 - -45 0.27 o.ko - . 16 2 - 3 372 - -.56 O.IIL 0.65 - .15 2 i ? : , II96 - - . 5 6 0.32 1.00 - . 12 ], T? k k?6 - • - . 5 6 0.37 1.00 - .12 Ho 6 m ^-21 i . 3 9 1.94 2 40 2.16 S'?6 6 7K 2 - 7 7 1.15 1.76 2.25 1 .83 % % ' 7 8^8 '. 15.76 5 . 6 9 + 6.13, 7.10 .9.62 8 k5 7 868 11.57 440 4-41 4-85 . 7 . 5 1 9 00 8 992 23.0 • 9 .03 5 .30 9.90 12.51 g 992 20.7 7.12 7.22 7.80 10.68 TABLE IV Potential with Different Solutions 18 B. and S. Soft Cu Wire Soln. 0 .05 N CuClg Time min 0 0 2 2.15 4.15 4.30 6.30 6.45 8.45 9.00 9-45 Load Kgm 0 3 3 ! 6 7 7 8 8 Kgm/cm2 Run #1 0 372 372 496 496 7W-8 % 868 992 992 0.00 +0.12 +0.24 +0.55 +0.52 +5.70 +3.83 +5.25 +4-.63 +5.70 +5.25 Run #2 Run #3 0.00 0 .00 +0.20 0.15 +0.25 0.17 +0.36 0 .26 +0.27 0.13 +4-46 3.55 +2.74 2.14 +5.38 5 .75 +3.70 4.17 +4-71 5 .20 +4.12 4»66 Time Lo ad min Kgm 0 0 0 3 2 3 2.15 4 4.15 4 4.3O A in 6 A O • J)W 6.45 7 8.45 7 9.00 8 9.45 8 Kgm/cm2 Run #1 0. . 372 372 496 m 868 992 992 0.00 - . 5 5 0.70 0.90 i . 5 5 4 . 3 0 3.70 12.25 7.95 15.35 10.78 Soln. 0 .05 N MgSO^ -4E mv Run #2 Run #3 0.00 0.17 0.15 0.65 0.16 2.83 2.37 12.10 6.70 11.33 9.03 0 .00 0.12 0.37 0.30 0.49 2.80 I. 4 l I I . 05 6.30 13.05 9.90 53 TABLE V? P o t e n t i a l vs Temperature 18 B; and S. S o f t Cu wire S o l n . 0.05 N CuSOj, F i x e d Load added = 8 Kgms = 992 Kgms/cm2 - A E i n mv temp Run 1 Run 2 Run 3 Run 4 Run '$ Run 6 Av o G 25 3.i+o 3.00 3.60 3.50 3-37 32 7.10 6.30 7.35 LO 8.10 7.15 7.25 7.00 ~ 7.25 7.25 7.33 50 8.80 9.85 8.90 11.75 11.25 10.11 55 11.35 12.60 12.75 12.85 .13.25 12.56 60 l L . f o l 5 4 o 13.85 14.20 13.10 16.50 14.58 65 1,6.20 16.25 18.70 16.84 17.25 18.75 17.33 75 28.00 23.75 24.25 23.50 25.50 26.00 25.16 85 29.65 32.50 30.00 31.80 31.75 34.75 31.74 TABLE VI F i n a l P o t e n t i a l a f t e r S t r e s s Value b e f o r e s t r e s s taken as zero p o t e n t i a l Time A f t e r S t r e s s Load P o t e n t i a l - n e g a t i v e mins Kgm/cm2 Scale 20 744- 0.33 9 744 0.26 47 744 0.44 *d 744 0.34 13 1120 1.13 84* 963 °.5° 152* 770 0.27 * From McDonnells' Data (15) 54 COPPER WERE SAMPLE  Pr o p e r t i e s of ^ Copper Subjected to U n i - D i r e c t i o n a l Stresses The f o l l o w i n g were manufactured under our order #F-36l311: 6# - #lli. A.W.G. s o l i d s o f t drawn copper w i r e . 6# - #14 A.W.G. hard drawn. 4# - #18 A.W.G. s o l i d s o f t drawn bare copper w i r e . 4# - #18 A.W.G. hard drawn. 2# - #22 A.W.G. s o l i d s o f t drawn copper w i r e . 2# - #22 A.W.G. hard drawn. A l l of the specimens were made from the same rod of copper the past h i s t o r y of which i s not recorded, but which came from our r e f i n e r y at Montreal. The drawing and annealing p r a c t i c e used i n the manufacture were as d e t a i l e d below: (a) l / 4 " **°d c o l d drawn on our machine #6 at 848 f e e t per minute; u s i n g new Ca r b a l l o y d i e s ; die passes, ( i . e . diameter reductions at each d i e ) , 0 .229" - 0 .204" -0.181" - 0.162" - 0.144" - 0.128" - 0.114" no annealing. (b) 0.114" copper wire c o l d drawn on our machine #104 at 490 f e e t per minute; using new diamond d i e s ; die passes, 0.1015" - 0 .0905" - 0.0718" - 0 .064" (#l4 A.W.G. hardwire). (c) 0 .064" copper wire c o l d drawn on our machine #104 at 490 f e e t per minute; using new diamond d i e s ; die passes, 0.057" - 0 .051" - 0 .0453" - 0 .0403" (#18 A.W.G. hard wire). (d) O .0403" copper wire c o l d drawn on our machine #24 at 806 f e e t per minute; using new diamond d i e s ; die passes, , 0 . 0 3 6 " - 0 .032" 0.0285" - 0.0253" (#22 A.W.G. hard wire). (e) to achieve the s o f t drawn specimens In each of the above s i z e s the f o l l o w i n g annealing process was employed. #14 A.W.G. and #18 A.W.G. hard copper - 1050°F i n B. and P. Furnace, r e t o r t time 90 minutes. #22 A.W.G. hard copper - steam annealed at 4 l0°F, l 6 h r . c y c l e . CANADA WIRE and GABLE COMPANY LIMITED 1200 Homer S t r e e t Vancouver, B.C. ^ 

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