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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  ii  ABSTRACT  The  effect of,unidirectional  electrode potential  o f c o p p e r was  w i t h b o t h s o f t c o p p e r and copper sulphate  and  magnitude of the several  cold  several  other e l e c t r o l y t e s .  and  the  Two obtained. effects.  (1) The  of  the  main c o n c l u s i o n s can Strain potential  is  the  in  i n t e r n a l e n e r g y due  (2)  Strain potential  dominant e f f e c t , but  problems.  I t has  o v e r 50  mv.  If stress  strain  others w i l l  the  possibly  be  r u p t u r e of  the  two  attaching the  a stress  of  be  992  pan.  results separate  of  a factor  the  in  film  change discarded.  corrosion  kgm/cm  active  2  can  direction  t o a non-homogeneous m e t a l under p l a s t i c  under p l a s t i c  and  by  d e f o r m a t i o n c a n n o t be  i g n o r e d as  a  and  a surface  second e f f e c t t h a t  s y s t e m w i l l be  more a c t i v e  solution.  drawn f r o m the  of  areas, which would u s u a l l y  w o u l d t h e r e f o r e be  on  area,  applying weights to  i s applied  be  unit  applied  r e s u l t of  to p l a s t i c  c a n n o t be  change i n  between s t r e s s e d  change i n t h e more a n o d i c o r  s y s t e m some p o t i o n s o f while  the  per  i s the  b e e n shown t h a t  cause a p o t e n t i a l of  that  of  f o u n d t o depend  S t r e s s was  w i r e s and  first effect  me  made i n m o s t i n s t a n c e s w i t h  of copper w i r e .  t o one  The  electrolyte in  N o r t h r u p p o t e n t i o m e t e r , was  pan  on  drawn c o p p e r i n s o l u t i o n s  M e a s u r e m e n t , w h i c h was  unstressed pairs  stress  S t u d i e s were made  time, temperature, stress  c o n c e n t r a t i o n of s o l u t i o n  a scale  studied.  e l e c t r o d e p o t e n t i a l was  variables,  L e e d s and  static  strain.  situated  highly  The  at g r a i n  susceptible  strain plastic boundaries, to  corrosion.  i i i . Failure  o f t h e m e t a l c o u l d t h e n be c a u s e d b y s t r e s s  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  metal  system.  concentration of the  i.  ACKNOWLEDGEMENT  I w i s h t o t h a n k D r . L . W. S h e m i l t f o r the very valuable  assistance given.  T h a n k s a r e 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 t h e g r a n t t h i s w o r k was c a r r i e d o u t .  a n d M r . W. McPadden  under which p a r t o f  TABLE OF CONTENTS Page Acknowledgement Abstract Table o f Contents L i s t of I l l u s t r a t i o n s INTRODUCTION  ^ ±± i v v 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  Figure  Page 6  1  Stress-Strain  2  P o t e n t i a l of Metal covered w i t h porous f i l m  12  3  S p h e r i c a l Test C e l l  15  k. C y l i n d r i c a l l\b. D e t a i l s 5  diagram  Test C e l l  |d"  o f C o n s t a n t Temperature  Bath  E f f e c t o f c o l d w o r k o f t h e m e t a l on c h a n g e in Electrode  20 25  potential  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 t i m e 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 t i m e  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 of temperature  3U-  12  S c a l e d Drawings  13  Constant Temperature  on e l e c t r o d e p o t e n t i a l  of test c e l l s Apparatus  4l  1.  INTRODUCTION Examination of the data obtained on t h e e f f e c t o f s t a t i c confused p i c t u r e . increase report  s t r e s s on g e n e r a l  from various  corrosion gives  Some a u t h o r s h a v e f o u n d s t a t i c  corrosion, others  workers  stress to  have f o u n d no e f f e c t and s t i l l  a decrease i n c o r r o s i o n .  a very  others  The e f f e c t seems s p e c i f i c  f o r t h e m e t a l and t h e e n v i r o n m e n t .  This  work r e p o r t s  some  both studies  t h a t h a v e b e e n made on t h e 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 b y unidirectional tensile  s t r e s s e s , i n order  importance i n c o r r o s i o n theory. confined  to various This  to evaluate  The i n v e s t i g a t i o n h a s b e e n  s i z e s and t y p e s o f c o p p e r  i n v e s t i g a t i o n represents  wire.  a continuation  w o r k c a r r i e d on a t t h i s U n i v e r s i t y b y M i n i a t o approach taken i s r a t h e r  their  of the  a n d McDonnell.  The  a r a d i c a l departure from the previous  a t t e m p t s t o r e l a t e t h e change i n i n t e r n a l e n e r g y c a u s e d b y d i s t o r t i o n o f t h e m e t a l t o t h e change i n e l e c t r o d e p o t e n t i a l . W h i l e t h i s change u n d o u b t a b l y h a s some e f f e c t on t h e e l e c t r o d e p o t e n t i a l , i t c a n be shown t h a t i t i s n o t t h e d o m i n a n t 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 e f f e c t s a r e 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 change o f e l e c t r o d e  potential with applied stress.  /  surface o f the  2.  PREVIOUS WORK  I n the p a s t 60 years there has been a l a r g e number of i n v e s t i g a t i o n s c a r r i e d out on the e f f e c t o f u n l - d l r e c t i o n a l s t r e s s e s on e l e c t r o d e p o t e n t i a l s . been very extensive  However, none o f these have  and i n g e n e r a l wherever comparison has been  p o s s i b l e there has been c o n s i d e r a b l e agreement i s not only c o n f i n e d e f f e c t o f various difficulty  to q u a n t i t y  This  dis-  but a l s o to the  v a r i a b l e s on the e l c t r o d e p o t e n t i a l .  i n comparing r e s u l t s i s the i n a b i l i t y  reproducible  A major  to o b t a i n  conditions.  The Dill  disagreement.  most f r e q u e n t l y quoted work i s t h a t o f Walker and  (1) who made a comprehensive recheck o f previous  work.  Their  main c r i t i c i s m o f Andrews ( 2 ) , who had measured the p o t e n t i a l between 20$ elongated s t e e l and o r d i n a r y was h i s method o f h a n d l i n g as a v a r i a b l e . doubtful  s t e e l i n NaCl s o l u t i o n ,  the samples, and h i s Ignoring  o f time  They concluded that Hamtuechen's (3) r e s u l t s were  since he d i d not a l l o w  to r e a c h e q u i l i b r i u m .  s u f f i c i e n t time f o r h i s samples  Hambuechen t e s t e d s t e e l , copper,  brass,  z i n c and wrought i r o n by s t r e s s i n g the samples up to t h e e l a s t i c l i m i t i n ferrous c h l o r i d e s o l u t i o n .  Walker and D i l l  samples by s t r e s s i n g up to the breaking solutions.  tested  point i n ferrous  steel  sulphate  T h e i r measurements were made p o t e n t i o m e t r i c a l l y w i t h  a calomel c e l l as r e f e r e n c e found was a c o n s i d e r a b l e  electrode.  The main e f f e c t they  electronegative*  Moore e l e c t r o n e g a t i v e means a g r e a t e r tendency f o r the metal t o form i r o n s , t h a t the metal becomes l e s s noble and t h a t i t i s more a n o d i c . (European and Nat. Bureau o f Standards convention).  effect  above t h e e l a s t i c  point.  After breaking  value w i t h time.  l i m i t r e a c h i n g 50 mv. a t t h e b r e a k i n g  the p o t e n t i a l returned  Below the e l a s t i c  limit  toward the i n i t i a l  they n o t i c e d  little  or no change i n p o t e n t i a l . S i m i l a r m e a s u r e m e n t s were made o n ^ - b r a s s o f c o p p e r and z i n c s a l t s b y M e r c i a  who o b t a i n e d  a t i v e c h a n g e s o f 0.2 mv a t t h e e l a s t i c l i m i t yield point.  (5)  cell  as r e f e r e n c e .  emphasizes the n e g l i g i b l e  p o t e n t i a l of brass.  Nikitin  (6,  a n d 1.0  mv. a t t h e  samples as r e f e r e n c e  electrodes.  A recent r e p o r t by  e f f e c t o f stress'- on t h e  7, 8) p u r s u e d t h e same  o f i n v e s t i g a t i o n on c o p p e r , s i l v e r  and i r o n , u s i n g  type  unstressed  Tensile deformation  m e t a l samples i n s o l u t i o n s o f t h e i r negative  electroneg-  These m e a s u r e m e n t s were a l s o made p o t e n t i o m e t r i c -  a l l y with a calomel Mears  i n solutions  o f the  own s a l t s r e s u l t e d i n  p o t e n t i a l c h a n g e s o f 7 mv. maximum a n d 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 o f 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 c h a n g e s s i n c e t h e y 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 potentials. 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 was  t e s t e d b y J a c q u e t and D r u e t  showed t h a t c o l d - w o r k i n g a b o u t Ij.0 - 50 mv.  (9)  i n 3% N a C l s o l u t i o n .  surfaces, They  c a u s e d an e l e c t r o n e g a t i v e c h a n g e o f  E v a n s a n d Simnade  (10)  while  studying  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 t h e c h a n g e s I n p o t e n t i a l o f 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  stresses.  A t any time c o m p r e s s i v e ~  stresses tensile the  gave more e l e c t r o p o g i t i v e stresses  more e l e c t r o n e g a t i v e  t e s t a r e a was  not  stressed.  same f i n a l p o t e n t i a l was  for  stress.  In  In n e u t r a l  stressed,  acid solutions  greater stress ranges.  more e l e c t r o p o s i t i v e  (11)  copper i n v a r y i n g solutions of  the  mirror  solutions  type g a l v a n o m e t e r .  (13)  by  (University  always  samples.  of  the  the  electrolyte.  o f CuSO|^, w i t h more d i l u t e  made w i t h  N/250  and  reports (12)  studies  and  Harwood o f the  o f C h i c a g o ) on  at t h i s U n i v e r s i t y )  on  of m e t a l s .  the  CUSO^  22,  coil 26  2l\. and  solutions.  German a c c o m p l i s h m e n t s i n  a b r i e f mention i n a recent  w o r k a t the  the  o f E.M..P. c e l l s ,  on  Measurement  a suspended  T e s t s were made on  I n s t i t u t e of  e f f e c t of s t r e s s e s  there  experimental evidence a v a i l a b l e  potentials  alter-  A n n e a l e d s p e c i m e n s were  p o t e n t i a l d e v e l o p e d was  electrodes  subjected to  was  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  A s i d e f r o m the  review  test area  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.  stress corrosion  the  r e p o r t e d attempt to determine  c o p p e r w i r e i n N/25  S.W.G  solutions  g r e a t e r c h a n g e s were f o u n d  e f f e c t of c o n c e n t r a t i o n d i f f e r e n c e s Jha  or  t h a n when  than u n s t r e s s e d c o l d worked  T h e r e i s one  Gatttam and  and  potentials  r e a c h e d whether the  compressed, extended, not nating  potentials,  seems t o be  (other  e f f e c t s of  little  t h a n the stress  on  data  on  the  Metals  the other obtained electrode  Harwood c o n c l u d e d , f r o m h i s r e v i e w  the  p u b l i s h e d r e s u l t s on  the  the  electrode  of metals, that despite  potentials  e f f e c t s of  stress  and  of  c o l d work  the  on  increasing  experimental evidence p o i n t i n g p o t e n t i a l under the i n f l u e n c e  t o a more  5.  electronegative  o f t e n s i l e s t r e s s , much r e s e a r c h  r e m a i n s t o be done t o c l e a r up t h e e x i s t i n g c o n f u s i o n a n d t o definitely establish special  attention  the r o l e  be p a i d  of stress.  He s u g g e s t e d  t o the methods o f s u r f a c e  that  preparation  thot to  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 ,  and^consideration  s h o u l d be g i v e n t o t h e p o l a r i z a t i o n b e h a v i o r o f t h e m e t a l in  system  s p e c i f i c e n v i r o n m e n t s 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  stress. The w o r k c a r r i e d most i n t e n s i v e potentials.  on a t t h i s U n i v e r s i t y  investigation  Miniato  r e p r e s e n t s the  as t o t h e n a t u r e o f s t r e s s  (II4.) h u n g p a i r s  of wires i n solutions  a d d e d w e i g h t s t o one w i r e t o o b s e r v e t h e e f f e c t o f s t r e s s the  electrode potential.  moving c o i l  galvanometer.  He c o n c l u d e d t h a t  s t r a i n i s produced by e i t h e r  difference  i s d e v e l o p e d when $.  i n t e r n a l or applied  corrosion  product of a stress p o t e n t i a l c e l l  potential  due t o t h e s t r e s s  behave e x a c t l y is the  i n the presence o f  external  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 .  stress potential  i sneglible.  curves f o rboth cold  He n o t e d t h a t t h e  drawn c o p p e r a n d b r a s s  up t o t h e e l a s t i c  curve l e v e l s o f f i r r e g u l a r l y .  I f the  i s i n s o l u b l e , the  as t h e i r s t r e s s - s t r a i n c u r v e s d o .  a linear relationship  on  A l l m e a s u r e m e n t s were made w i t h a  some e l e c t r o l y t e s , a p o t e n t i a l  stresses  and  limit,  Miniato also  using v a r y i n g concentrations of NaCl, that  That i s , there after  concluded,  the s t r e s s  potential  i s independent of 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 . 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  which  was n o t i n v e s t i g a t e d  The much  b e y o n d the  elastic  l i m i t of  the  metal.  6.  (15)  McDonnell  c o n t i n u e d M i n i a t o ' s w o r k 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 made h i s m e a s u r e m e n t s u s i n g e i t h e r coil  galvanometer.  Despite a large  to reproduce M i n i a t o ' s r e s u l t s . follows  : ( i ) the  p r o d u c e d by  d i r e c t i o n and  magnitude of  potential  elongation  change p r o d u c e d b y  s o l u t i o n was  a logarithmic  changes t h a t  c o u l d be  c o p p e r had  the  attributed  a f i l m to form.  He  that  strain potential  changes are  the  s t r a i n on  and  that  little  condition  influence  on  the  of  the  electrode  as  change (11)  electrolyte  the magnitude  of of  c o p p e r w i r e i n CuSOlj.  to time  (iv)  d i d not  concluded from these primarily  the  unable  summarized  potential  electrolyte for  time f o r the  (iii)  to s t r e s s i n g  been exposed to the  be  was  electrode potential  stressing  relationship  a moving  t e s t s he  H i s r e s u l t s can  appreciably influence  copper u n l e s s accompanied by  the  number o f  s t r a i n i n g c o p p e r d e p e n d s u p o n the  s t r a i n d i d not  the  a p o t e n t i o m e t e r or  he  potential occur  a sufficient observations  surface  metal electrode  potential.  unless  effects has  THEORETICAL CONSIDERATIONS  In considering electrode  the  i n f l u e n c e o f s t r e s s upon  p o t e n t i a l of m e t a l s , I t i s d e s i r e a b l e  b r i e f d i s c u s s i o n , o f t h e n a t u r e o f s t r e s s and e f f e c t s of  s t r e s s upon the  o f the m e t a l  the  to begin with  a d e s c r i p t i o n of  a 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  system. i  S t r e s s maybe d e f i n e d t h a t are  s e t up  as t h e  w i t h i n a b o d y on  the  i n t e n s i t y of f o r c e a p p l i c a t i o n of  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. change i n d i m e n s i o n s t h a t a c c o m p a n i e s t h e i t maybe e l a s t i c s t r e s s has  or p l a s t i c  external  Strain i s  development of  (i.e. i t still  exists after  been r e l i e v e d , l e a v i n g a permanent When a m e t a l i s s u b j e c t e d  reaction  the stresses  the  deformation).  t o an e x t e r n a l l o a d , as  cold-working,  i t i s d e f o r m e d , and  the  d e f o r m a t i o n or  b e h a v i o u r can  be  the  s t r e s s - s t r a i n diagram  shown i n F i g u r e  c h a r a c t e r i s e d by 1.  A l o n g the  s t r a i n i s p r o p o r t i o n a l t o the above t h e e l a s t i c exists,  and  limit  plastic  is elastic.  ( A ) , t h i s p r o p o r t i o n a l i t y no  d e f o r m a t i o n has  taken place.  mechanical processes,  s u c h as d r a w i n g , r o l l i n g  the  and  amount o f e l a s t i c  before and  the  i s not  flow  l i n e a r p o r t i o n o f the c u r v e , s t r e s s and  plastic  In  and  deformation that  f r a c t u r e d e p e n d s upon t h e m a g n i t u d e o f t h e s t a t e of s t r e s s which i s produced. a well defined physical constant,  and  The  by  the  However, longer complex  extrusion, occurs applied  elastic  load  limit  o f t e n i t i s more  8. difficult  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 simple t e n s i o n t e s t . conceivable  that p l a s t i c  scale a tl o c a l i z e d  I t seems  d e f o r m a t i o n may o c c u r o n a m i c r o s c o p i c  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).  ramPlastic  Str-gih  Total  Elastic ^  Strain  Str-alh  Stress Strom Curve F13 1 •^Jftien a m e t a l metal.  I t i s obvious  much o f w h i c h significant  i s d i s s i p a t e d i n the form  fraction  energy  changes occur i n the  t h a t w o r k i s b e i n g done o n t h e m e t a l o fheat.  as l a t e n t energy  l e v e l o f the system.  which  system,  However, a  o f t h i s work, r a n g i n g f r o m 5 t o  s t o r e d up b y t h e m e t a l the i n t e r n a l  i s deformed i n t e r n a l  i s  serves t o increase  I t i s this increasei n  9. i n t e r n a l energy r e s u l t i n g from  the s t r a i n h a r d e n i n g p r o c e s s  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 and c h e m i c a l b e h a v i o u r stressed metals.  The  v a l u e o f s t r e s s and introduced into  changes i n the  of s t r e s s e d metals  to  physical  as c o m p a r e d t o  un-  a r e a u n d e r t h e s t r e s s - s t r a i n c u r v e f o r any  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  t h e m e t a l d u r i n g t h e d e f o r m a t i o n p r o c e s s and  b e e n shown t o be  as h i g h as 15 c a l o r i e s / g m ( 2 1 ) .  For  has  copper  g wire under a t e n s i l e 0.2 by  calories/gm.  s t r e s s o f 10  Plastic  dynes t h i s i s a p p r o x i m a t e l y  deformation i s generally  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  ductility properties.  accompanied  a decrease  i n the  I n a d d i t i o n to these p r o p e r t y changes,  atomic, 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  o c c u r as a r e s u l t o f d e f o r m a t i o n .  The  alterations  process of  plastic  d e f o r m a t i o n i n v o l v e s s u c h 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 , warping  of c r y s t a l p l a n e s , r o t a t i o n  orientation effect, structure into  and  and e l o n g a t i o n o f  a g e n e r a l breakdown of the  a highly disorganised state.  The  may  twinning,  grains,  crystal  extent to  which  any o f t h e s e p r o c e s s e s o c c u r s i s d e p e n d e n t u p o n t h e m a g n i t u d e o f t h e s t r a i n , t h e s t r a i n r a t e , and t h e t e m p e r a t u r e a t w h i c h t h e deformation occurs  (22).  I n o t h e r words p l a s t i c  deformation i s  e essentially  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  scale  As i n d i c a t e d e a r l i e r , p l a s t i c tends  to increase t h e i r  should manifest i t s e l f  i n t e r n a l energy, by  as  well.  deformation of  metals  and t h i s e n e r g y  i n c r e a s i n g the heat  of s o l u t i o n  increase and  10.  by s h i f t i n g the electrode potential i n a more anodic (electronegative)  direction.  This is to be expected from the  relationship A F r -nFE * i n which  s  (1)  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 i n t e r n a l energy accompanying c o l d 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 p l a s t i c s t r a i n energy stored i n the specimen ( 2 1 ) .  However, as i t i s well known for metals,  suoh  p l a s t i c deformation i s not a homogeneous process and very uneven d i s t r i b u t i o n of suoh latent energy caused by cold working or similar stresses Is the aotual condition found. equation 1 cannot be used or modified  C l e a r l y then*  to determine the  change of electrode potential due to p l a s t i c deformation.  That  a change w i l l occur due to deformation i s c e r t a i n but i t s magnitude 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 p l a s t i c deformation.  11.  the e l e c t r o d e p o t e n t i a l . suggested  (10, 1 5 ) .  I t has, further,  ( 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 s u c h a s c o p p e r w o u l d be t o c a u s e new s p l i t s in  the oxide f i l m  r e a c t i o n would copper  and t o broaden  and t h e s u r r o u n d i n g a t m o s p h e r e . t h e n be due t o t h i s  the p o t e n t i a l w i l l film  A  exposed  The c h a n g e i n t h e  r u p t u r e i n the f i l m and  return to i t s original  v a l u e as t h e o x i d e  i s being repaired. 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  solution originally will  and b r e a k s  and deepen e x i s t i n g ones.  t h e n be p o s s i b l e b e t w e e n t h e n e w l y  p o t e n t i a l would  been  f r e e from i o n s o f the metal i n q u e s t i o n  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  present.  This w i l l  e s p e c i a l l y be t h e c a s e i f t h e f i l m  displays  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 than the o t h e r . side The  a porous  oxide f i l m  The p o t e n t i a l  at a point just  out-  ( 1 9 ) maybe o b t a i n e d g r a p h i c a l l y .  c u r r e n t f l o w i n g between the f i l m  exposed  a t pores i n the f i l m  of f i l m  and m e t a l t o a p p r o a c h  (as c a t h o d e )  (as a n o d e ) w i l l  cause  and t h e m e t a l the p o t e n t i a l s  one a n o t h e r , a s i n d i c a t e d b y t h e  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  just  out-  s i d e t h e f i l m w i l l be r e p r e s e n t e d b y t h e p o i n t P on t h e 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 b e t w e e n t h e two c u r v e s , where R i s t h e r e s i s t a n c e : for  i R i s t h e r e s i d u a l E=M.P w h i c h w i l l  current i through r e s i s t a n c e  R.  exactly suffice  to force  12.  Current —*  '  P o t e h t i o l o f M e t a l  •  Covered,  w t f i ° -  '  If  i  t h e f i l m p o r o s i t y i s d e c r e a s e d , as s u g g e s t e d b y t h e  b r o k e n l i n e , we s h a l l  I n c r e a s e R and s t e e p e n t h e a n o d i c  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 t h e a n o d i c a r e a i s d i m i n i s h e d ; since  t h e c a t h o d i c c u r v e w i l l h a r d l y be a f f e c t e d , I t f o l l o w s  that the p o t e n t i a l w i l l  rise  the p o r o s i t y o f the f i l m ,  t o p"*".  I n g e n e r a l the s m a l l e r  t h e h i g h e r w i l l be t h e 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 t h e p o t e n t i a l w i l l when f i l m - r e p a i r p r e d o m i n a t e s , predominates.  would  s i n c e s t r e s s e s would  then cause  decrease  when f i l m  breakdown  This i s probably the key t o p o t e n t i a l  caused by s t r a i n , and w o u l d  and t o f a l l  tend to r i s e  a fall  cause f i l m  i n potential.  the p o r o s i t y o f the f i l m  changes  breakdown  Compressive  forces  and hence cause an  13. increase  i n potential.  E v a n s and Simnade General F i l m  T h i s was shown t o be t h e c a s e by-  (10) Theory  I t h a s b e e n shown, a b o v e , t h a t t h e p o t e n t i a l o f an electrode  t e n d s t o r i s e when f i l m - r e p a i r , o r g r o w t h  predominates,  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 of the coating t o the r e a c t a n t s . corrosion product f i l m i s less protective  A porous  t h a n one  Whether o r n o t c o r r o s i o n p r o d u c t f i l m s a r e p o r o u s  non-porous. apparently  d e p e n d s on t h e r e l a t i v e v o l u m e o f t h e c o r r o s i o n p r o d u c t t o t h e v o l u m e o f t h e m e t a l consumed i n f o r m i n g i t . . and B e d w o r t h where:  (18)  compared  Pilling  showed t h a t f o r o x i d a t i o n i f t h e r a t i o  Md/^  M I s the molecular weight of the oxide D i s the d e n s i t y o f the oxide m I s the atomic wt. o f the metal m u l t i p l i e d by the no. o f m e t a l atoms i n t h e o x i d e f o r m u l a d i s the metal  density.  i s g r e a t e r than u n i t y , the oxide c o a t i n g i s p r o t e c t i v e , when l e s s t h a n u n i t y , i t i s n o n - p r o t e c t i v e .  Metals accordingly  c a n be d i v i d e d i n t o two g r o u p s . 1.  One g r o u p  i s composed o f t h e l i g h t e r m e t a l s w i t h p o r o u s  o x i d e s s m a l l e r i n v o l u m e t h a n t h e e q u i v a l e n t m e t a l consumed i n producing the o x i d e s .  These m e t a l s a t c o n s t a n t t e m p e r a t u r e  at a rate nearly constant w i t h time. and m a g n e s i u m (MgO) , w h i c h h a v e r a t i o s and 0 . 7 9  respectively.  oxidize  E x a m p l e s a r e c a l c i u m (CaO o f M d / ^ e q u a l t o 0.61j.  2. A l u m i n i u m and the h e a v i e r of greater  volume t h a n t h e e q u i v a l e n t  second group.  o f the time.  (CUgO) a n d c h r o m i u m  e q u a l t o 1.60,  equations  ( i ) The r e c t i l i n e a r y=k.t + k  Examples are n i c k e l  conditions:  2  equation  y = k j l o g (kjj_ t + The p a r a b o l i c = k t + k 6  (2I4.) b y w h i c h common m e t a l s  equation  ( i i ) The l o g a r i t h m i c  2  oxidize  ( C ^ O ^ ) w h i c h have r a t i o s o f  a r e known t o o x i d i z e u n d e r o r d i n a r y  y  they  to  1 ..71. a n d 2.03 r e s p e c t i v e l y (19) .  There are three  (iii)  m e t a l consumed make u p , t h e  U n d e r some c o n d i t i o n s  p r o p o r t i o n a l l y t o the logarithm (NiO), copper  oxides  Many m e t a l s o f t h i s g r o u p o x i d i z e a c c o r d i n g  the p a r a b o l i c e q u a t i o n .  Md/^  metals w i t h non-porous  k-5) .  equation ?  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 w o u l d be o u t o f p l a c e .  equations  15.  APPARATUS a n d PROCEDURE  Apparatus The a p p a r a t u s simple.  used i n the i n v e s t i g a t i o n i s quite  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 , t h e t e s t c e l l and  the d e t e c t i o n apparatus. by r e f e r e n c e  The t e s t c e l l  c a n b e s t be d e s c r i b e d  t o a diagram  our • Figure 4-  Figure 3  Figure 3 i s a sketch of the f i r s t c e l l used. of a s p h e r i c a l g l a s s bulb  on w h i c h t h e 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 . arranged  to.enable  attached  The c a p i l l a r y t u b e s a r e  s o t h a t t h e two t e s t w i r e s c a n p a s s t h r o u g h  shown i n t h e d i a g r a m . bulb  I tconsists  the c e l l  A small funnel i s attached  t o the g l a s s  t o be f i l l e d w i t h s o l u t i o n .  t o the bottom o f the bulb  t h e c e l l as  A tap i s  ( n o t shown-) t o d r a i n t h e c e l l  16. when r e q u i r e d . necessity  This c e l l  to regulate  w o r k e d w e l l when t h e r e was n o  the temperature o f the s o l u t i o n , however,  when t h e e f f e c t o f t e m p e r a t u r e  on t h e c h a n g e 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 e r a t u r e b a t h and i n s e r t t h e c e l l necessary t o re-design the c e l l erature bath. li.  The f i n a l  cell  i n the b a t h .  a c o n s t a n t tempI t was f o u n d  f o r i n s e r t i o n i n a c o n s t a n t temp-  s e l e c t e d was t h a t shown i n f i g u r e  I t h a s t h e 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 t h e 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 u s e d . the  bottom  cells  Drainage  two c a p i l l a r i e s .  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  S c a l e d drawings o f the two'types o f  are included i n the appendix.  In both types of 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 t h e c a p i l l a r i e s the  and t h e ends o f  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 t h e a i d o f 'Cenco' p a r a -  rubber tape.  T h i s t a p e was f o u n d v e r y s a t i s f a c t o r y  vented the s o l u t i o n from l e a k i n g from the c e l l time i t d i d n o t r e s i s t  since  i t pre-  a n d a t t h e same  the e l o n g a t i o n of the t e s t  wires.  M e a s u r e m e n t s w e r e made w i t h b a r e c o p p e r w i r e o f s t a n d a r d s i z e 18 A.W.G  a n d 22 A...W.G.  and s o f t w i r e were t e s t e d .  Both h a r d cold-drawn copper w i r e The m e c h a n i c a l h i s t o r y o f t h e w i r e  i s known e x a c t l y a n d i s i n c l u d e d i n t h e a p p e n d i x . The tilled  water.  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 When d e - o x y g e n a t e d  s o l u t i o n s were  n i t r o g e n was b u b b l e d t h r o u g h t h e s o l u t i o n f o r 15  required, minutes.  dis-  17. Preparation o f Test The and  Wires.  w i r e s were c u t i n t o t h e r e q u i r e d l e n g t h  (70cms.)  stored i n a cupboard.  No a t t e m p t  was made t o p r o t e c t t h e  w i r e from the atmosphere.  Just prior  t o use  f u l l y cleaned w i t h carbon alcohol.  tetrachloride  C l e a n i n g was a c c o m p l i s h e d  or d i r t f i l m that coated  and f i n a l l y w i t h  s p e c i f i e d s o l v e n t s . The  t h e w i r e was t h u s r e m o v e d , 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 f r o m exposure t o the  methyl  by wiping each wire s e v e r a l  times w i t h l e n s paper soaked w i t h the grease  t h e w i r e s were c a r e -  to that resulting  atmosphere.  Procedure. The of the c e l l  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  a n d s u s p e n d e d f r o m a wooden f r a m e .  the  A s c a l e p a n was  a t t a c h e d t o t h e w i r e w h i c h was t o b e l o a d e d w h i l e ttte weight en  capillaries  light  (500gms.) was added t o t h e u n l o a d e d w i r e s o a s t o s t r a i g h t -  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 t h e c h o s e n w i r e b y  s i m p l y l o a d i n g the s c a l e p a n .  G r e a t c a r e was t a k e n  l o a d o n w i t h o u t c a u s i n g an i m p a c t ,  Since impact  t o place the  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 wire connected detection apparatus. befweert  ial b~efore v  and  two wir-es  **af  the p a i r o f t e s t w i r e s t o the  When t h e c h o s e n w i r e was l o a d e d »vieo*vrevJ. T k e  tmtiaf Valve o f  the  p'^ntial  t h e l o a d was a d d e d was s u b t r a c t e d f r o m t h e f i n a l  t h e c h a n g e i n e l e c t r o d e p o t e n t i a l was t h u s c o m p u t e d .  ment o f t h e p o t e n t i a l s were made a t a n y d e s i r e d t i m e . necessary  potentvalue  Measure-  I t was  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 b e t w e e n t h e 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 , a s w i l l be shown, a s t r i c t l y  constant  18. p o t e n t i a l c a n n o t be a t t a i n e d .  T h r e e m e t h o d s were u s e d i n  d e t e c t i n g t h e 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 m e t h o d r e q u i r e d two o p e r a t o r s . potentiometer Northrup all  (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  M o d e l #63U-359 r e a d i n g t o V l O O  times.  Leeds and  o f a mv) i n b a l a n c e a t  When t h e l o a d was a d d e d t h e o p e r a t o r was a b l e t o  f o l l o w the p o t e n t i a l by keeping (2) D.C. E l e c t r o n i c The  One o p e r a t o r k e p t t h e  Voltmeter  the potentiometer  balanced.  Method  l e a d s f r o m t h e v o l t m e t e r / ( c i r c u i t o f B u r r , L a n e a n d NIms  25) w e r e a t t a c h e d t o t h e two w i r e s c o n s i d e r e d a n d t h e n t h e 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  from the galvanometer s c a l e .  directly  However, t h i s method t h o u g h  factory i nprinciple  d i d n o t work t o o w e l l .  the v o l t m e t e r tended  to d r i f t  I t was f o u n d  and c o n s e q u e n t l y  h a d t o be  satisthat cali-  brated a f t e r each s e r i e s o f r e a d i n g s .  This voltmeter, a f t e r a  s e r i e s o f a l t e r a t i o n s , was d i s c a r d e d .  Apparently  o f the. v o l t m e t e r I s c o r r e c t h u t t h e s e n s i t i v i t y  the p r i n c i p l e  i s too great f o r  our p u r p o s e 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 in  operation.  (3) Speedomax M e t h o d A Leeds and Northrup  #806I|.73 Speedomax was o b t a i n e d  during  the l a t t e r  s t a g e s o f t h e i n v e s t i g a t i o n a n d was u s e d w h e r e v e r  possible.  The u s e o f t h e speedomax was l i m i t e d b y t h e f a c t  t h e r a n g e c o v e r e d b y t h e i n s t r u m e n t was f r o m 22 t o 50 mv.  that  19. For necessary  the f i n a l  p a r t o f t h e i n v e s t i g a t i o n i t was  to construct a constant  be m a i n t a i n e d  temperature bath which  t o w i t h i n 0.1°C o f t h e t e m p e r a t u r e d e s i r e d .  was  f o r a r a n g e o f t e m p e r a t u r e f r o m 20 t o 100°C.  the  operation  This  D e t a i l s as t o  a n d c o n s t r u c t i o n o f s u c h a b a t h a r e 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 c a n be o b t a i n e d such a bath w i t h the t e s t c e l l s  from the diagram of  and h e a t i n g element I n c l u d e d  (  B).  Figure k  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 t h e  r e s u l t s report i n previous  w o r k h a v e b e e n t o a l a r g e d e g r e e due  t o c o n d i t i o n s t h a t c a n n o t be r e p r o d u c e d . this  could  author's  I t has,  p o l i c y to c a r e f u l l y describe  t h e r e f o r e , been  e a c h p r o c e d u r e so t h a t  t h e e x a c t p r o c e d u r e c a n be r e p r o d u c e d b y a n y 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 c a n be c o n v e n i e n t l y  following  d i v i d e d i n t o the  sections:  (1) L o a d v s . Change i n E l e c t r o d e P o t e n t i a l The and  l o a d was added a t a f i x e d d e f i n i t e  (i m i n . )  t h e 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 t h e v a r i o u s  loads recorded. and  time i n t e r v a l  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  a t a r o o m t e m p e r a t u r e o f 21°C 1 1 ° .  p o t e n t i a l between the l o a d e d the p o t e n t i o m e t e r .  Measurements o f t h e  a n d u n l o a d e d w i r e s were made w i t h  S e v e n t r i a l s were made u n d e r  identical  conditions. (2) Change o f E l e c t r o d e  Potential with  Time.  A f i x e d l o a d was a d d e d t o t h e s c a l e p a n a n d t h e p o t e n t i a l b e t w e e n t h e two w i r e s m e a s u r e d a t r e g u l a r intervals.  pre-determined  A f t e r the p o t e n t i a l had returned  to close to i t s  PLAN VIEW  CROSS  - SECTIONAL  V / £ W  AA All  Constant  Temperature  Apparatus  pp'  o r i g i n a l v a l u e an a d d i t i o n a l potential  again measured.  3 o r ly t i m e s .  w e i g h t was a d d e d a n d t h e  I n a f e w c a s e s t h i s was r e p e a t e d  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 r o o m t e m p e r a t u r e o f 21°C t 1 ° C  Measurement o f t h e  p o t e n t i a l was made w i t h t h e p o t e n t i o m e t e r b u t l a t e r t h e s p e e d omax was u s e d .  The u s e o f t h e 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 c o n d u c t t h e r u n s a t a h i g h e r temperature  (85°G).  was  out i n the constant temperature b a t h .  carried  (3) E f f e c t The  Hence t h e l a t t e r p a r t o f t h e e x p e r i m e n t  o f Concentration of the S o l u t i o n i n the C e l l  e f f e c t o f the c o n c e n t r a t i o n o f t h e e l e c t r o l y t e  change i n e l e c t r o d e p o t e n t i a l  on t h e  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  electrolyte  s t u d i e d i n t h i s c a s e 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.  Fixed  l o a d s were added t o t h e s c a l e p a n a n d t h e maximum c h a n g e i n electrode potential noted.  After  the passage  of half  a minute  an a d d i t i o n a l w e i g h t was a d d e d and t h e maximum e l e c t r o d e potential times;  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  M e a s u r e m e n t s were made w i t h a p o t e n t i o m e t e r .  Effect  of Different  Electrolytes.  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 t h e 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 used.  The f o l l o w i n g  were t h e e l e c t r o l y t e s  were  used:  O.O^N CuSO^ O.O^N  MgSO^  0.G5N C u C l (5) E f f e c t The  2  o f Temperature  cells  i n t h e c o n s t a n t t e m p e r a t u r e b a t h were f i l l e d  with  22. s o l u t i o n one h a l f hour b e f o r e b e i n g loaded.  T h i s was necessary  to enable the s o l u t i o n to a t t a i n the temperature T h i s temperature  ranged from 25° t o 85°C.  of the b a t h .  The s e l e c t e d wire was  then loaded w i t h the f i x e d weight, 8kgm, and the change i n p o t e n t i a l d e t e c t e d by the p o t e n t i o m e t e r .  To o b t a i n the most  probable r e s u l t s i x t r i a l s were made at each s e l e c t e d The  speedomax was a l s o used as a f u r t h e r check o f some o f the  results (6)  temperature.  Obtained.  Change of P o t e n t i a l w i t h Time a t Zero  Load  The v a r i a t i o n o f p o t e n t i a l w i t h time w i t h zero l o a d was i n v e s t i g a t e d at a c o n s t a n t temperature  of 21 '+ 1 ° C  T h i s was  accomplished by suspending the wires i n a 0.05N CuSOj^ s o l u t i o n and t a k i n g r e a d i n g s o f p o t e n t i a l between the two wires a t v a r i o u s i n t e r v a l s over a 21+. hour p e r i o d .  Nine p a i r s of wires were t e s t e d .  No attempt was made to determine l e n g t h of wire exposed  to the s o l u t i o n .  t h a t t h i s e f f e c t was. n e g l i g i b l e .  the e f f e c t of the  McDonnell (15) r e p o r t e d  In every case the l e n g t h o f  wire exposed was the maximum allowed by the c e l l s used i . e . V~> cms for  the s p h e r i c a l c e l l  and 36 cms. f o r the c y l i n d r i c a l  cell.  23. RESULTS OBTAINED The r e s u l t s o b t a i n e d i n some cases d u p l i c a t e d the r e s u l t s obtained by McDonnell(15) and other workers, but  this  i s d e s i r e a b l e since the r e p o r t s on p r e v i o u s work have been h i g h l y conflicting.  The r e s u l t s r e p o r t e d here are e a s i l y r e p r o d u c i b l e .  A l l r e s u l t s were checked many as 10  at l e a s t 3 times and i n some cases as  times and i n not a s i n g l e 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 r e p e a t i n g the  under e x a c t l y s i m i l a r c o n d i t i o n s w i t h new  experiment  wires and a f r e s h  solution. 1.  In a l l cases examined the s o f t copper wires gave  g r e a t e r changes In p o t e n t i a l than the cold-drawn  copper w i r e s .  In most cases I t was n o t p o s s i b l e to measure the change i n e l e c t r o d e p o t e n t i a l of cold-drawn  copper wire u s i n g the same  l o a d i n g system as that used f o r the s o f t copper id re..  Any  change  i n p o t e n t i a l d e t e c t e d f o r the hard copper wire was e x c e e d i n g l y small  (0.2 mv.)  effects.  However, i f i t had been p o s s i b l e to s t r a i n the wire  permanently occurred.  and might e a s i l y have been due to p o l a r i z a t i o n  a g r e a t e r change i n e l e c t r o d e p o t e n t i a l would have A g r e a t e r s t r e s s was found n e c e s s a r y to produce  p a r t i c u l a r change of p o t e n t i a l at the second s t r e s s i n g than r e q u i r e d at the f i r s t  stressing  (Figure 5 . )  f o l l o w s from the f a c t t h a t p l a s t i c  a was  This naturally  s t r a i n decreases the  of the metal and since i t can be shown (Figures 6 ,  7)  ductility  that the  2k.  potential  effects  a r e d i r e c t l y d e p e n d e n t on t h e amount o f  elongation. 2.  No s i g n i f i c a n t d i f f e r e n c e s  oxygenated s o l u t i o n s dissolved  was f o u n d f o r d e -  as o p p o s e d t o o r d i n a r y s o l u t i o n s  oxygen and n i t r o g e n .  containing  However, t h e m e t h o d o f d e - o x y g e n -  a t i o n might have been a t f a u l t , oxygen i n the s o l u t i o n g e n e r a l l y  since  the c o n c e n t r a t i o n o f  e x e r t s some i n f l u e n c e  rate  of f i l m formation.  The e f f e c t o f a c o n t r o l l e d  (e.g.  N ) was a l s o f o u n d n e g l i g i b l e i n t h e p r o c e d u r e  on t h e  atmosphere followed.  2  3. F o r a l l t e s t s on c o p p e r i n CuSOj^ s o l u t i o n ,  electro  - n e g a t i v e p o t e n t i a l c h a n g e s were o b t a i n e d f o r t h e a p p l i c a t i o n o f tensile  stresses. For  a series  c o p p e r ) i n 0.05N was  CUSOJ^  o f seven p a i r s  (#18  of wires  A.W.G  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  noted by the a d d i t i o n  soft stress  of constant increments of load a t  c o n s t a n t t i m e i n t e r v a l s , a n d r e c o r d i n g t h e maximum change i n p o t e n t i a l f o r each increment o f load. in electrode  potential  A l i n e a r p l o t o f change  i n m i l l i v o l t s between s t r e s s e d  and u n -  2 stressed  wires against stress  E a c h c u r v e h a s two c r i t i c a l  i n kgm/cm  points,  c o r r e s p o n d i n g t o t h e two p o i n t s seven d e t e r m i n a t i o n s . in  i s g i v e n i n F i g u r e 7.  and the s t r e s s  are remarkably constant f o r a l l  The r a n g e o f r e p r o d u c i b i l i t y o f r e s u l t s  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  o b t a i n e d a r e a t a p p r o x i m a t e l y 6 x 1CH kgm/cm Beyond the second c r i t i c a l p o i n t further potential  values  change.  points  a n d 8 x 10^ kgm/cm .  there i s l i t t l e  evidence of  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 obtained 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.  1 2  21 SWG annealed Cu ' 2 5 CUS0 Reloadinq of (I) afferunloa dinq  4  UJ 2 < X  o UJ  o CL UJ  >  o o  ' or ho  UJ  1  . UJ  4  J  L  J  8  l_  10  K 6 M / CM * XI0 " 2  LOAD  3  U  re  Fig  ure 6  27.  o b t a i n e d by M c D o n n e l l f o r  d i f f e r e n t d i a m e t e r copper w i r e s , I t  can be seen t h a t w i t h a s m a l l e r d i a m e t e r w i r e the f i r s t  critical  p o i n t o c c u r s a t . a l o a d v a l u e l e s s than t h a t o f 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  copper w i r e i n 0 . 0 5 N CuSO]^ s o l u t i o n i s a p p r o x i m a t e l y  5.75  soft mv.,  w h i l e t h a t f o r 21 S.W.G. annealed copper I n O.Oi^ CuSO^ i s about 1+.75 mv.  P a r t o f t h i s d i f f e r e n c e i s due, no doubt, t o the  d i f f e r e n c e i n c o n c e n t r a t i o n o f 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 o f t e n s i l e s t r e s s tended t o drop t o z e r o w i t h t i m e , and removal of the a p p l i e d s t r e s s caused l i t t l e  o r no change i n the p o t e n t i a l .  I t should be n o t e d t h a t the p o t e n t i a l change never d i d r e a c h z e r o b u t seemed t o l e v e l o f f a t a v a l u e s l i g h t l y above z e r o . For copper w i r e s i n CuSO^ s o l u t i o n the p o t e n t i a l time were l o g a r i t h m i c i n c h a r a c t e r . work w i t h McDonnell's work (15)  curves  Combining the r e s u l t s o f t h i s i t can be seen t h a t the s l o p e  of p o t e n t i a l change v s l o g a r i t h m o f time p l o t i s dependent on the s i z e o f w i r e used i n c r e a s i n g ( i n n e g a t i v e v a l u e ) 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 g i v e n i n F i g u r e s 8 and 9«  An i m p o r t a n t  o b s e r v a t i o n was made i n t h a t an; i n d u c t i o n  p e r i o d f o r the w i r e i n the e l e c t r o l y t e i s a p p a r e n t l y before stress.  necessary  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 o f The l e n g t h o f t h e i n d u c t i o n p e r i o d , p r o v i d e d i t was o f  s u f f i c i e n t l e n g t h (15 m i n u t e s ) , d i d n o t a f f e c t the magnitude of the change I n p o t e n t i a l .  (Table I )  >  8 00  o  10  30  20 TIME  Figure  IN  MINUTES  8  (Table Jl)  40  30.  5. By varying the concentration of the CuS0[j_ solution from 0..SN to 0.0005.N i t was found that both the magnitude and rate of change of the electrode p o t e n t i a l caused by stress tended to increase.  The change from 0.005N to 0.0005N  was s i g n i f i c a n t hut small, and introduces the p o s s i b i l i t y of a l i m i t i n g concentration for such an e f f e c t .  The r e s u l t s of  concentration versus electrode p o t e n t i a l for two different loads are plotted i n 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 e l e c t r o l y t e s have been found to give considerably different potential-time curves.  The sense, the  magnitude and the rate of change of the p o t e n t i a l caused by stress application a l l vary with the e l e c t r o l y t e .  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 about 5«5 (iv) 0 . 7 N NaCl  electronegative  change maximum, change  about 1 1 . 5 mv. maximum, (v)  1.0N Na S0]^ electronegative 2  change  about 11 mv. maximum. Results  (IV) and (v) are those obtained by McDonnell (15) •  THE E F F E C T OF CONCN OF E L E C ON STRESS POTENTIAL  18 B 8 S  SOFT  CJS0  4  COPPER  SOLN  OOI  o oa o o 0 0 0  LOAD  992  KGM/CM  2 LOAD  86 8  KGM/CM^  1  ELECTRONEGATIVE  Fiqure 10  CHANfrE  IN  (Table. JL)  POTENTIAL  33.. Results  ( i ) ,(ii)  are the average o f 3 t r i a l s  and ( i i i )  with  each type o f e l e c t r o l y t e .  7. changes  The e f f e c t  o f temperature  on e l e c t r o d e  potential  U s i n g ^ 1 8 A.W.G. s o f t  was a l s o i n v e s t i g a t e d .  copper  w i r e i n 0 . 0 5 N CuSOj^ s o l u t i o n , i t was f o u n d t h a t f o r a c o n s t a n t  2 a p p l i c a t i o n o f 992 kgms p e r cm  stress  w h i c h i s a b o u t ij. mv  at 25 C r i s e s  change r i s e s  to well  t o o v e r 30 mv.  Q  the same l o a d and u s i n g  a solution  o v e r 5 0 mv.  t h e maximum p o t e n t i a l a t 85°C.  With  o f 0.005N CuSO]^, the p o t e n t i a l  a t 85°C.  The r e l a t i o n s h i p  b e t w e e n the l o g a r i t h m o f the e l e c t r o d e p o t e n t i a l change and t h e reciprocal  o f the a b s o l u t e t e m p e r a t u r e  i s linear.  Six readings  a t e a c h t e m p e r a t u r e were made and t h e a v e r a g e o f the r e a d i n g s were u s e d i n t h e p l o t that  the l a s t  do n o t f a l l points.  two p o i n t s  straight  The s l o p e o f t h e l i n e  o f the l i n e  v a l u e s an e q u a t i o n r e l a t i n g with  I t w i l l be n o t i c e d  i . e . a t a temperature  e x a c t l y on-the  and t h e i n t e r c e p t  11.  obtained i n Figure  line  o f 25°C and 32°C  through the o t h e r seven  d log (BP) i s e q u a l t o 1 . 5 2 d (1/T) ~ i s equal to $  x  1Q ,  From t h e s e two  t h e change i n e l e c t r o d e  potential  t e m p e r a t u r e c a n be o b t a i n e d :  log  (EP) = 1 . 5 2 x 1 0  3  l / T + 5.71}-.  This e q u a t i o n i s , o b v i o u s l y , c o n f i n e d under which  the i n v e s t i g a t i o n was c a r r i e d  i n 0 . 0 5 N CuSO^ s o l u t i o n .  ,  to the c o n d i t i o n s  out, i . e . copper wire  J  EFFECT OF TEMPERATURE  ON CHANG-E OF ELECTRODE  POTENTIAL AT A FIXED LOAD  Figure II  (Totfe^  35.  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 stress  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 of i n c r e a s e c o r r o s i v i t y .  suggestive  Prom time p o t e n t i a l c u r v e s however, i t  i s f o u n d t h a t s u c h 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 t i m e , i . e . the s t r e s s e d m e t a l 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 s i m p l y as the exposure o f new m e t a l s u r f a c e due  t o s t r e s s , and the g r a d u a l f o r m a t i o n o f an i m p e r v i o u s  f i l m due t o c o r r o s i o n p r o d u c t s and the s u r r o u n d i n g medium. in  surface  formed f r o m the m e t a l s u r f a c e  The n e c e s s i t y o f an i n d u c t i o n p e r i o d  the e l e c t r o l y t e ; the v a r i a t i o n o f p o t e n t i a l change w i t h i n c r e a s e d  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 t h a t b r e a k i n g and making of a s u r f a c e 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  f o r m a t i o n o f 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  o b t a i n e d are t h e r e f o r e t o be  I t i s u s u a l l y c o n s i d e r e d t h a t a l a y e r o f cuprous i s p r e s e n t on copper i n aqueous s o l u t i o n s .  expected. oxide  T h i s tends t o be  r e p l a c e d by one o f 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 o b s e r v e d w i t h CuSO^ and w i t h  CuCl  2  i s t h e r e f o r e understandable.  The c o n c e n t r a t i o n changes  w i l l i n t u r n a f f e c t n o t o n l y the r a t e o f f o r m a t i o n o f an oxide l a y e r a t newly exposed p o r t i o n s , b u t w i l l potential.  a l s o a f f e c t the  I t i s considered also that t e n s i l e s t r e s s i n g with i t s  36. exposure o f f r e s h metal and the r e s u l t a n t f o r m a t i o n of s u r f a c e l a y e r s w i l l give equilibrium  a new balance to the anodic and cathodic  on the s u r f a c e  o f the cppper.  areas  This i n turn a f f e c t s  the degree of l o c a l p o l a r i z a t i o n and hence the o v e r a l l p o t e n t i a l effect. The  r e s u l t s o b t a i n e d f o r the p o t e n t i a l - l o a d  curves  i n d i c a t e that the p o t e n t i a l change produced i s p r o p o r t i o n a l to the new surface  area exposed p e r u n i t lengJfah o f w i r e .  The  curves, however, i n d i c a t e 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 i n d i c a t e d by the graphs  (6, 7 ) i s d e c e p t i v e s i n c e i t  i n d i c a t e s that above a c e r t a i n l o a d no i n c r e a s e change i s p o s s i b l e . by The  In p o t e n t i a l  That t h i s was n o t the case was demonstrated  adding a l a r g e l o a d  (5 kgm) to the c r i t i c a l l o a d n  obtained.  w i r e , under t h i s l o a d , elongated u n t i l rupture and the p o t e n t i a l  increased  i n a n e g a t i v e d i r e c t i o n u n t i l the wire r u p t u r e d .  Obviously then, the l i m i t i s that value a t t a i n e d when the wire breaks i . e . when no f r e s h metal i s exposed.  The curve o b t a i n e d  w i t h i t s d e c r e a s i n g p o t e n t i a l change p e r u n i t of l o a d can be exp l a i n e d by the decrease i n d u c t i l i t y of worked m e t a l s .  Clearly  then, the p h y s i c a l 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 b e f o r e any c o n s i d e r a t i o n of the e f f e c t s on s t r a i n on e l e c t r o d e  p o t e n t i a l s can be  studied.  S o f t , or annealed copper s t r e s s - s t r a i n curve has no l i n e a r p o r t i o n , hence a l i n e a r r e l a t i o n s h i p between p o t e n t i a l and l o a d i s n o t to be  expected and i s , indeed, n o t o b t a i n e d . The  e f f e c t o f temperature on the magnitude of the  37. potential  change v e r s u s the r e c i p r o c a l  erature yields is usually  a straight line.  and  that  This indicates  p o t e n t i a l due t o s t r e s s t h i s change i n p o t e n t i a l  Tt»e e x a c t r e l a t i o n s h i p b e t w e e n r a t e i s n o t known.  that  been o b t a i n e d .  dependence involving  the change i n  corresponds to a rate i s proportional  and e l e c t r o d e  f o r s o f t c o p p e r i n 0.05N  reaction  t o the r a t e  potential  o f fUt A  change  solution  CUSO[L  has  I t i s expected that f o r a series of 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 s u c h e q u a t i o n s c a n be  u s e c a n be made o f them, h o w e v e r , u n t i l  between r a t e  temp-  An e q u a t i o n s h o w i n g t h e t e m p e r a t u r e d e p e n d e n c e o f  strain potentials  Little  This temperature  g i v e n b y an e q u a t i o n o f t h e A r r h e n i u s t y p e  an e n e r g y o f a c t i v a t i o n . electrode  of the absolute  and e l e c t r o d e  obtained.  a relationship  p o t e n t i a l change i s  established.  I t h a s b e e n shown t h a t when c o p p e r s u f f e r s p l a s t i c deformation there i s a large  change i n p o t e n t i a l  n e g a t i v e d i r e c t i o n , and t h a t  this potential  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  approaching assymtotically initial  (Figure  approaches the i n i t i a l v a l u e .  8).  the  slower  finally  g r e a t e r than the  This value  The f i r s t  of 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 repair  effect will repaired. return  never  C l e a r l y then, t h i s indicates  d i f f e r e n t e f f e c t s caused by p l a s t i c s t r a i n . that  change d e c r e a s e s i n  some v a l u e a l i t t l e  value before s t r a i n  i n the e l e c t r o -  two  effect  o f f s e t by  t o the f i l m , hence the p o t e n t i a l change c a u s e d by t h i s gradually  return  t o z e r o as t h e s u r f a c e f i l m i s  The p o t e n t i a l c h a n g e , i t h a s b e e n shown, d o e s n o t  t o z e r o , t h i s c a n be e x p l a i n e d b y t h e f a c t t h a t  the metal  38. s y s t e m has  been permanently a l t e r e d  e n e r g y i n c r e a s e d g i v i n g r i s e t o an  and  has  had  Its  Internal  increase i n potential  of  the  i n t h i s w o r k may  be  metal. The  l i m i t a t i o n s t h a t have e x i s t e d  s u m m a r i z e d as (1) The  follows: p o t e n t ! o m e t r i e method of measurement a l l o w s a  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 balance i s  There i s always the  imposition  s u c h a m e t h o d , and  the  d e f i n i t e l y h a v e an  important  (2) The in  lack  and  thereby caused  in  will  effect.  of h o m o g e n e i t y i n the  effects  obtained.  a s l i g h t measuring current  polarization effects  i t s surface oxide l a y e r  reversible  of  possible  remove t h e  r e d u c e the  metal i t s e l f  p o s s i b i l i t y of  possible  as w e l l  as  completely  reproducibility.  Improvements Little e v e r the  can  be  done a b o u t t h e  f i r s t l i m i t a t i o n can  e a s i l y be  quick response e l e c t r o n i c  v o l t m e t e r or  speedomax was  l a t e r p a r t of  was  u s e d i n the  f o u n d i d e a l f o r the  c o v e r e d was  not  purpose.  s a t i s f a c t o r y but  o b t a i n e d w h i c h w o u l d e n a b l e the range .  s e c o n d l i m i t a t i o n , howr e c t i f i e d by a.speedomax.  a  A  this investigation  U n f o r t u n a t e l y , the a new  either  and  range  s l i d e wire could  i n s t r u m e n t t o c o v e r the  be desired  39.  BIBLIOGRAPHY  .1.  Walker W., and D i l l C , T r a n s . Am. E l e c t r o c h e m . S o c , 11, 153 (1907).  2.  Andrews T., P r o c . I n s t . C i v i l Eng. (Br.) 11,8. 356,  (l89ii).  3.  Hambuechen C , B u l l . U n i v . W i s e , Eng. S e r i e s 2, 8 , 235 (1900)  ii.  M e r c i a P-. D., Met. Chem. Eng., l£, 3 2 1 ,  5.  Mears R. B., M e t a l P r o g r e s s , 1L8, 105  6.  N i k i t i n L. V., Compt. r e n d . acad. s c i . U. S. S. R, 17_,  (191.6). .  107  (1937).  ,  N i k i t i n L. V., J . Gen. Chem. (U. S. S. R ) , %  7 9 V (1939).  8.  N i k i t i n L. V., J . Gen. Chem (U, S . S . R ) , 1 1 ,  II4.6 O.9I4L)  9.  Druet Y. and Jacquet P. A., Metaux e t C o r r o s i o n , 2 2 , 139 (191+-7)  7.  1 0 . Evans U. R. and Simnade M. T., P r o c . Roy. Soc. (London), 11.  Gautam L. R. and J h a J . B.  188A. 3 7 2 , 1 9 4 6 . P r o c . I n d i a n Acad. S c i . , 18A, 350  (1953)  12.  Nangle C. A.  13*  Harwood J . J . C o r r o s i o n ,  11L.  M i n i a t o 0 . K. Measurement o f S t r e s s P o t e n t i a l s . M. A. S c . T h e s i s i n Chem. Eng., U n i v . o f B . C. (l9i|-7).  15.  McDonnell B. E f f e c t o f S t 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. S c . T h e s i s i n 6hem. Eng., U n i v . o f B. G. (19IL8)  A i r M a t e r i a l Command Tech. Report FT - R 1131 - ND (19)4-7). 6, no 8 , 2ij-9  (1950)  4-0. 16.  S h e m i l t L. W.  17.  B a n n i s t e r L. C. and Evans U. R.  18.  P i l l i n g N. B. and Bedworth R. E.  19.  E v a n s . 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 A r n o l d and Co. London 1937 pg i S S X X X K  20.  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 A r n o l d and Co. London 194-8 Pg 1 2 2 .  21.  T a y l o r G. I . and Quinney H.  22.  Bohnenblush H. P. and Dewez P., T r a n s . A. S. M. E. 70, 222 (1948).  23.  P e t e r s o n R. E., T r a n s . A. S. M. E.  24.  Evans U. R.  25  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 r e s s e s on E l e c t r o d e P o t e n t i a l s . Paper p r e s e n t e d a t Symposium on E l e c t r o c h e m i s t r y and C o r r o s i o n . Ottawa, Nov. 1950. J . Chem Soc.  l4&4*  (1930)  J . I n s t . M e t a l s 2£, 534* (1923)  P r o c . Roy. S o c . (London) 143A, 307 (1934).  Trans Am. E l e c t r o c h e m .  A.P.M.  55-19.  Soc. 83_, 335 (1943)  B u r r H. S., Lane C. T., and Nims L. P. Y a l e J . B i o l , and Med.  (1933).  % 6£, 1 9 3 6 ) .  Cor\startt  TewpenatMre. Figure.  13  Apparatus  P o t e n t i a l vs S t r e s s  TABLE I  18 B . and S. S o f t Cu wire  Soln'.  (A)  N/20 CuSO^  Load Kgm 2  3 4 5 6 7 9 11 18 B. and S. S o f t Cu wire Load Kgm 3  Potent. D i f f mv  Kgm/cm 372 620  2  I  +0.45 +0.24  -O.70 -3.61 -4.58 -4.32 • -4-37  m  7 8 9 11  992 1120 1360  1ft B. and S, 'a«ft Cu w i r ~ Kgm/cm2  Load Kgm  248 496 620  ! 2  m  7 9 11  1120 . 1360  .R R : nd S.. fl  Load Kgm  h  6.3 6.8 8.3  ™  wire  (B)  S o l n . N/20 CuSO^ ~A E  mv 0.06 0.27 1.21 4.II 5.09  4.83 4.88 (C)  s » m N/20 CuSO), Potent. D i f f . mv 1-47 l.lp. I.32 0.31 -1.17 -2.16 -2.16  -A E mv 0.02 0.08 0.17 1.80 2.66 3.65 3.65 (D)  S o l i i N/20 CuSO), Potent. D i f f . mv ^.0.96 -1.01 -1.22 -1.77 -2.67 -3.00' -3.49  -A E  mv 0.05 0.10 0.31 0.86 .1.77 2.10 2.58  18 B. and S. S o f t Cu w i r e 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  18 B. and S. S o f t Cu w i r e Load Kgm  2.0 3.0 3.5 .  Kgm/cm* 2IL8 ,  372  IL.O  k  5.1 6.5 7.5  558 633 806 930 .  k-5  18 B. and S. S o f t Cu w i r e 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  Soln...  N/20 CuSO^• -4E  Potent. D i f f . mv  mv 0.11  -0.11 -0.26  0.26 O.kiL  -O.kk  -1.51+-  I . 54  -ii.07  4.07 4.71  -2.10  .  2.10  -4.71  -4.63  II.  -1L.89  S o l n . N/20 CuS0| Potent. D i f f mv  - 0.03 -O.OIL  - 0.07 - 0 . 2J4. - -047 .87 -- 02.k5 -2.82  63  4.89 r  -4 E mv  0 .03 . O.OI4. 0.07 O..2I4. 047 0.87  2.L5 .2.82  S o l n . N/20 CuSO^. Potent. D i f f . mv  -4. E  mv  - 0.08 •* 0.12 - 0.30  0.08  - 1.58 -347  1.58  -0.78  0.12 0.30 0.78 347  • -5.51*  -5.95 - 6.J1I - 7.83  6.Iii  7.83  Potential  TABLE I I  vs Time at  45,  Various  Fixed Loads 18 B. and S. Soft Cu Wire Time mlns. o  6 13 14 15 16 17  Load Kgm o  0 6  18  .  N/20 CuSO), . - ' 2 Kgm/cm 744  '  19'; 21 22 oh  25 26 28 40 50 51 52 53 54 55 56 57 58  Potent. D i f f . -mv. 0.33 0.33 -1.42 -1.07 -0.79 -0.66 -0.53 -0.48 -0.4£ -0.41 -O.36 -0.32 -0.29 -0.25 -O.23 -0.23 -0.21 -0.19  -0.14  0.00  Q  10  992  • 1240  -2.52 -2.29 - 2.00  -1.75 -1.57 -1.44 -.1.33 ~2.53 -2.00  > ^ E mv. 0.00 0.00 1.75 1.40 1.12 0.99 0.86 0.81 .0.74 O.69 0.65 0.62 0.58 0.56 0/56 0.54 0.52 0.47 0.33 2.85 2.62 2.33 2:08 1.90 1.77 1.66 2.86 2.33  46  18 B. a n d S. Cu w i r e Time  mins 0 lh  Load  Kgm  S o l n N/20 CuSOj^ J : / > ... 1 . l;LS?.:  Kgm/cm  0  0  6  7.-44  17 18 19 20 21 22  23 36 37 •38 39 40 41 42 4L 4g ll  8  992  9  1120  48 52  ^ ft  2  •  mv  +0.67 +0.68 . +0.18 0.29 0.35 O.38 O.38 0.38 0.39  0.00 0.00 0.50 0.38 0.32 0.30 0.30 .0.29 0.85  0.4o 0.4l  -2.59 -2.17 -1.83 -1.64  -1.31 -1.19 -1.02 -2.36 -2.05 -1.77 -1.56  10  1240  -AE  Potent. D i f f . mv  -1.44  4Q  |6  (A)  -1.42 -2.43 -1.85 -1.63  0.27  0.26 3.26 2.84 2.51 2.31 2.12 1.98 1.87 1.70 3.03 2.72  2.442.24 2.10  3.11 2.53'  5? 57 58  -1-31 -1.21  2.30 2.12 1.98 1.88  -1.02  1.78 1.70  60 65 70  -0.95 -0.67 -O.46  1.62 1.34 1.14  St  - " l - ^ : - l . l l  18 Time mins 10 10 11 12  B. and S. S o f t Cu w i r e Load Kgm  S o l n . N/20  Kgm/cm 0  0 6  Ikk'  8  992  i  16  ^7  18 20 21 22 23 25 27 29 38 it  fl 66 67 68 69 70 72  2  CuSO^  Potent. D i f f mv 1.92  (B) —  AE mv  0.00  48  18 B. and S. S o f t Cu w i r e Time mins  0  Load Kgm  Soln.  Kgm/cm  0 4 5  0 496 620  6  744-  2  N/20  CUSO^  Potent. D i f f mv  0.29 0.11 -0.27 -0.18 -0.08 -0.05 -2.00 -1.5? -I.24  -1.00  -O.79  -0.65 -o.£6 -0.47 -0.40 8  992  ^0.34  -3.60 -349 -2.69 -2.4l -2.20 -2.01 -1.84  -1.71  10  11  1240  -1.5: 5 -1.4 -3.32 -3.02 -2.79  1360  -2.44 ^4.10  -2.63 --•^ -3.38  -A.E mv  0.00 0.18 0,55 0.47 0.36 0.34 2.2" 1.8 1.53 1.29 1.08 0.9k  0.84 0.76 0.69 0.63 3.8" 3.4' 2.98 2.70 2.49 2.30 2.13 2.09 1.84 1.72 3 3.61 3.31 3.31 3.08 3.08 2.92 2.73 4.40  3,67  h9 18 B. and S. Time mins  Soft Cu wire Load Kgm  Soln. 0  Kgm/cm2  Potent. D i f f mv  0 k  5-96  -.13 -.15 -.12  5  620  -.hi  6  0  N/20 CuSO),  -.34 -.32  71*4  -2.57 -2.19 -1.76  -1.53 -1.38 -1.26  -1.17  -1.09 8  11  992  1360  -O.98  -3.20 -3.00 -2.1+5 ^2.27 -2.13 -2.01 -1.78 -1.72 ~2.61L -2.to -2 .111 -1.99  t-  50  TABLE I I I  Concentration  18 B . a n d S.  0.05 Time mine  S o f t Cu w i r e  e  2 2.15 4.15  4.30 6.45 8.45  9.00  9.45- . 0.5 Time mins 0 . 0  2  2.l£ 4.15  4.30  6.30  6.45 8.45  9.00  9-45  Potential  SolnO-<?5CuS0),  N CuSO)j Load Kgm  0  vs Electrode  0 3 3 4 4  6  A u  7 7 8 8  - 4 E mv Kgm/cm  Run #1  2  0 372 372 496 496 744 7ii4 868 868 992 992  -  0.12 0.12 0.12 0.12 0.12 0.12 0.25 0.25 0.37 0.37 0 0. H 3.11 3 1.57 1.57 2.61 2.61 2.50 2.50  Run #2  'Run #3  o0.11 .ll -0.07 0.06 0.06 0.05 0.10 0.10 0 . 0 4 0.09 0.09 0.03 1.49 1.49 . 0.86 0.Q1 0.91 0.45 2 . 6 l 1.98 2.61 1.71 1.03 2.31 2.18 •• 2.31 2.81 1.54 2.81  N CuSOlj. Load Kgm  9  3 3  4 4  6  6 7 7 8 8  -A E Kgm/cm  0 372 372  496  1I96  744 7IA 868 868 992 992  2  Run #1  mv  Run #2  0.11 0.02 0.02 0.01 0.32 0.18 0.60 0.33 0:;70 0.49  R u n #3  0.03 . 0.06 . 0.03 0.03 0.17 0.14  0.58 0.35 0.75 0.59  51 0 . 0 0 5 N.CuS0)[. Time mins  -•^E my  Load Kgm  2  0 3 3  0 0 2 2.15  0  5-30  6 6 7 7 8 8  6.3O 6.fo 8.45 9.00 945  0 . 0 0 0 5 N CuS0) Time mins 0 "'  2  Load Kgm  -  2i?:,  ], T?  Ho  S'?6  % % ' 8 k5 9 00  3  3  k  6 6 7 7 8 g  Run #3  R u n #2  0 . 0 4  372 372 J4.96 L96 7hk 7lijl 868 868 992 992  i I  MS  R i m #1  Kgm/cm  0 . 0 4  0.0Q O.kb 2.66 1.69 8.51 I4..38 10.03 II.OIL  0.06  0.05 0.05  O.Oii 0.0k li.16 2.16 74 9 3.81+ 7-3U5.l6  0.66 O.lii 2.91 0.68 3131 2.19  f  . Kgm/cm -  , Run #1 Run #2  2  372  II96  m  8^8 868 992 992  0.27  -.56 • -.56 ^-21 i.39 -77 1.15 15.76 5.6 11.57 23.0 • 9.03 20.7 7.12  0.32 0.37  -  k?6  7K  -45  -  372  -.56  2  '.  Run #3. Run # i i  +  O.IIL  1.94  1.76 6.13,  440 4-41 9  5.30 7.22  o.ko 0.65  1.00 1.00 2  ^. Ron**? -.16  -.15  -.12 -.12 2.16 1.83 7.10 .9.62 4-85 . 7 . 5 1 9.90 12.51 7.80 10.68  40 2.25  TABLE IV  P o t e n t i a l with D i f f e r e n t  18 B. and S. 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  S o l n . 0 . 0 5 N CuClg  S o f t Cu Wire  Kgm/cm  2  0 372 372 496 496 7W8% 868 992 992  Solutions  Run #1  Run #2  Run #3  0.00 +0.12 +0.24 +0.55 +0.52 +5.70 +3.83 +5.25 +4-.63 +5.70 +5.25  0.00 +0.20 +0.25 +0.36 +0.27 +4-46 +2.74 +5.38 +3.70  0.00 0.15 0.17 0.26 0.13 3.55 2.14 5.75 4.17 5.20 4»66  +4-71 +4.12  S o l n . 0 . 0 5 N MgSO^ Time min  Lo ad Kgm  0 0 2  0 3 3  2.15  4 4 6  4.15  4.3O A i J)W n O• 6.45  8.45  9.00  9.45  A  7 7 8 8  Kgm/cm  2  0. . 372 372 496  m 868 992 992  Run #1  - 4 E mv Run #2  Run #3  0.00 -.55 0.70 0.90 i.55 4.30 3.70 12.25 7.95 15.35 10.78  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 v s Temperature  18 B; a n d S. S o f t C u w i r e Soln. F i x e d L o a d a d d e d = 8 Kgms  0.05  N CuSOj,  = 992 Kgms/cm2  temp o  Run 1  - A E i n mv Run 3 Run 4  Run 2  Run  '$  Run 6  Av  G  25 32 LO  50 55 60 65 75 85 TABLE V I  3.i+o  3.00  7.10 8.10 8.80 11.35 lL.fo 1,6.20 28.00 29.65 Final  After mins  after  stress  Stress  20 9 47 13 84* 152*  (15)  3-37  7.00 ~ 11.75 12.85 14.20 16.84 23.50 31.80  7.25 11.25 .13.25 13.10 17.25 25.50 31.75  7.25 16.50 18.75 26.00 34.75  Stress t a k e n as z e r o  Load Kgm/cm  744744 744 744 1120 963 770  *d  * From M c D o n n e l l s ' D a t a  3.50  7.35 7.25 8.90 12.75 13.85 18.70 24.25 30.00  Potential  Value before Time  3.60  6.30 7.15 9.85 12.60 l54o 16.25 23.75 32.50  2  potential  Potential-negative Scale  0.33 0.26  0.44 0.34 1.13 °.5° 0.27  7.33 10.11 12.56 14.58 17.33 25.16 31.74  54  COPPER WERE SAMPLE Properties  o f ^Copper S u b j e c t e d t o 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 m a n u f a c t u r e d under our o r d e r # F - 3 6 l 3 1 1 : 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. h a r d 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. h a r d 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. h a r d drawn. A l l o f the specimens were made f r o m the same r o d o f copper the p a s t h i s t o r y o f w h i c h i s n o t r e c o r d e d , b u t w h i c h came f r o m our r e f i n e r y a t M o n t r e a l . The drawing and a n n e a l i n g 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 a t 848 f e e t p e r m i n u t e ; u s i n g new C a r b a l l o y d i e s ; d i e p a s s e s , ( i . e . d i a m e t e r r e d u c t i o n s a t each d i e ) , 0 . 2 2 9 " - 0 . 2 0 4 " 0 . 1 8 1 " - 0 . 1 6 2 " - 0 . 1 4 4 " - 0 . 1 2 8 " - 0.114" no a n n e a l i n g . (b) 0.114" copper w i r e c o l d drawn on our machine #104 a t 490 f e e t p e r m i n u t e ; u s i n g new diamond d i e s ; d i e p a s s e s , 0.1015" - 0 . 0 9 0 5 " - 0.0718" - 0 . 0 6 4 " ( # l 4 A.W.G. hardwire). (c) 0 . 0 6 4 " copper w i r e c o l d drawn on our machine #104 a t 490 f e e t p e r m i n u t e ; u s i n g new diamond d i e s ; d i e p a s s e s , 0 . 0 5 7 " - 0 . 0 5 1 " - 0 . 0 4 5 3 " - 0 . 0 4 0 3 " (#18 A.W.G. h a r d w i r e ) . (d) O.0403" copper w i r e c o l d drawn on our machine #24 a t 806 f e e t p e r m i n u t e ; u s i n g new diamond d i e s ; d i e p a s s e s , , 0 . 0 3 6 " - 0.032" 0 . 0 2 8 5 " - 0.0253" (#22 A.W.G. h a r d w i r e ) . (e) t o a c h i e v e the s o f t drawn specimens I n each o f the above s i z e s the f o l l o w i n g a n n e a l i n g p r o c e s s was employed. #14 A.W.G. and #18 A.W.G. h a r d copper - 1050°F i n B. and P. F u r n a c e , r e t o r t time 90 m i n u t e s . #22 A.W.G. h a r d copper - steam a n n e a l e d a t 4 l 0 ° F , l6 hr. cycle. CANADA WIRE and GABLE COMPANY LIMITED 1200 Homer S t r e e t Vancouver, B.C.  ^  

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