Solute redistribution during internal oxidation of Ag-Cd alloys containing tin as an additive

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Solute Redistribution During Internal Oxidation of Ag-Cd Alloys Containing Tin as an Additive YUAN-SHOU S H E N , E D W A R D J. Z D A N U K , A N D RICHARD H. K R O C K

DURING

a s t u d y of the internal oxidation of A g - C d a l l o y s , i t h a s b e e n f o u n d that t h e m o r p h o l o g y o f t h e CdO p a r t i c l e c a n be m o d i f i e d by a d d i n g a s m a l l a m o u n t o f t i n a s a n a d d i t i v e . It i s i m p o r t a n t t o h a v e i n f o r m a t i o n c o n c e r n i n g t h e d i s t r i b u t i o n of t h e a d d i t i v e s t o u n d e r s t a n d t h e m e c h a n i s m of n u c l e a t i o n a n d g r o w t h of t h e o x i d e p a r t i c l e s a s a f f e c t e d by t h e a d d i t i v e . T h e e l e c t r o n m i c r o p r o b e a n a l y s i s in t h i s w o r k s h o w s a high d e g r e e o f correlation between t h e distribution o f t h e a d d i t i v e t i n a n d CdO p a r t i c l e s i n t h e A g - C d O material. EXPERIMENTAL

WORK

In this investigation, t h e purity of t h e m a t e r i a l used was A g - 9 9 . 9 5 p c t , C d - 9 9 . 9 5 p c t , S n - 9 9 . 9 5 p c t . T h e c o m p o s i t i o n o f t h e a l l o y w a s A g - 9 . 0 wt p c t C d - 0 . 2 wt p c t S n . T h e m a t e r i a l w a s a l l o y e d in a n i n d u c t i o n f u r n a c e i n a n a r g o n a t m o s p h e r e a n d t h e n c a s t into a n i r o n m o l d . T h e i n g o t w a s r o l l e d to a s l a b o f a t h i c k n e s s o f 1 • 5 ~- m . S l u g s o f ~- i n . i n d i a m w e r e p u n c h e d o u t f r o m t h e s l a b , a n d t h e n a i r o x i d i z e d at 8 0 0 ° C in a tube f u r n a c e f o r 9 6 h r . B o t h ends o f t h e tube were o p e n . T h e furn a c e a t m o s p h e r e was c i r c u l a t e d w i t h a f a n at t h e e n d of the f u r n a c e t u b e ; h e n c e , t h e p a r t i a l p r e s s u r e o f o x y g e n w a s a p p r o x i m a t e l y 0.2 a t m . A f t e r oxidation the slugs w e r e sectioned and prep a r e d f o r m e t a l l o g r a p h i c s t u d y by s t a n d a r d m e t h o d s . A l l s p e c i m e n s w e r e e x a m i n e d by l i g h t m i c r o s c o p y a n d by t h e e l e c t r o n m i c r o p r o b e i n t h e u n e t c h e d c o n dition. R E S U L T S A N D DISCUSSION M a c r o s c o p i c a l l y , two z o n e s a r e o b s e r v e d i n t h e cross-section; the oxidized o u t e r c a s e , and the unoxYUAN-SHOU SHEN, EDWARD J. ZDANUK, and RICHARD H. KROCK are Staff Members and Group Manager, Materials and Metallurgy, respectively,P . R. Mallory and Co., Inc., Laboratory for Physical Science, Burlington, Mass. Manuscript submitted March 2 5 , 1 9 7 1 . 2960-.VOLUME 2 , OCTOBER 1971

F i g . 1--Internal o x i d i z e d Ag-9 C d alloy. S h o w s the o x i d i z e d c a s e a n d p a r t of the c o r e . magnification 77 t i m e s . i d i z e d i n n e r c o r e . T h e case d i s p l a y s a two-phase m o r p h o l o g y , t h e oxide p a r t i c l e s d i s p e r s e d in t h e silv e r m a t r i x . T h e r e a r e p a r t

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