Chemical interdiffusion and kirkendall shifts in silver- cadmium alloys
- PDF / 697,516 Bytes
- 7 Pages / 613 x 788.28 pts Page_size
- 20 Downloads / 213 Views
E V E R s i n c e K i r k e n d a l l ~ f i r s t r e p o r t e d and S m i g e l s k a s and K i r k e n d a l l 2 and o t h e r s v e r i f i e d the e x i s t e n c e of a m a s s flow r e l a t i v e to the i n i t i a l i n t e r f a c e of a b r a s s c o p p e r d i f f u s i o n couple, m a n y i n v e s t i g a t o r s have b e e n s t i m u l a t e d to m e a s u r e t h i s e f f e c t and c o n s i d e r i t s i m p l i c a t i o n s for the n a t u r e of c h e m i c a l i n t e r d i f f u s i o n . Although the bulk of t h e s e s t u d i e s w e r e e x p e r i m e n t a l in n a t u r e , p h e n o m e n o l o g i c a l and a t o m i s t i c e x p l a n a t i o n s a l s o followed f r o m t h o s e with t h e o r e t i c a l i n t e r e s t s . D a r k e n , a in one of the f i r s t a n a l y s e s , showed that c h e m i c a l i n t e r d i f f u s i o n c o e f f i c i e n t s in b i n a r y s y s t e m s could be c a l c u l a t e d f r o m t r a c e r diffusion and t h e r m o dynamic activity data. Darken's equations were subs e q u e n t l y m o d i f i e d by Manning for the v a c a n c y m e c h a n i s m of diffusion 4-7 to include a d d i t i o n a l t e r m s to a c c o u n t for c o r r e l a t i o n and v a c a n c y wind e f f e c t s in a chemical concentration gradient. Manning's atomisitic viewpoint, t a k i n g into account the e f f e c t of a flow of i m p e r f e c t i o n s on a t o m j u m p p r o b a b i l i t i e s , g i v e s r i s e to a " v a c a n c y flow t e r m " which i n f l u e n c e s the equat i o n s r e l a t i n g i n t r i n s i c diffusion c o e f f i c i e n t s , i n t e r d i f f u s i o n c o e f f i c i e n t s , K i r k e n d a l l s h i f t s and a t o m f l u x e s to t r a c e r d i f f u s i o n c o e f f i c i e n t s . E x p e r i m e n t a l v e r i f i c a t i o n of the v a c a n c y wind effect was f i r s t r e p o r t e d in 19678 in the s i l v e r - c a d m i u m s y s t e m . A d d i t i o n a l c o n f i r m a t i o n s followed. W o r k i n g with the s i l v e r gold s y s t e m , M e y e r ~ m e a s u r e d the e f f e c t s of p r e s s u r e and v a c a n c y flow on the K i r k e n d a l l shift, finding v e r y good a g r e e m e n t b e t w e e n e x p e r i m e n t and the v a c a n c y wind m o d e l . E x p e r i m e n t s b y D a l l w i t z 1~ with s i l v e r gold a l l o y s p r o v i d e d f u r t h e r v e r i f i c a t i o n . O t h e r r e s e a r c h e r s w o r k i n g with a v a r i e t y of b i n a r y a l l o y s y s t e m s , C u - Z n , 11 A g - C d , 12,~a and V - T i , ~4 have d e m o n s t r a t e d the i m p o r t a n c e of the v a c a n c y wind in i n t e r diffusion. In a l l of the a b o v e - m e n t i o n e d s t u d i e s , none had a s t h e i r m a i n o b j e c t i v e , the m e a s u r e m e n t of the K i r k e n d a l l shift i t s e l f . Such m e a s u r e m e n t s , i n c l u d i n g c o m p a r i s o n s of d i r e c t ( t r a v e l i n g m i c r o s c o p e ) and ind i r e c t (Matano
Data Loading...
