Discontinuous precipitation processes in supersaturated copper-antimony solid solutions
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PREDEL
AND
WOLFGANG
GUST
The k i n e t i c a s p e c t s of d i s c o n t i n u o u s p r e c i p i t a t i o n in s u p e r s a t u r a t e d Cu-Sb s o l i d s o l u t i o n s h as b e e n i n v e s t i g a t e d q u a n t i t a t i v e l y f o r the f i r s t t i m e . A f i n e l y and c o a r s e l y d i s p e r s e d p r e c i p i t a t i o n mode is found. The c o a r s e l y l a m e l l a r r e g i o n s have an i n t e r l a m e l l a r s p a c i n g about 2 to 6 t i m e s as l a r g e as that o b s e r v e d in the f i n e l y l a r n e l l a r c e l l s . The l a r g e - a n g l e b o u n d a r i e s a r e the p r e f e r r e d n u c l e a t i o n s i t e s f o r the f i n e l y l a m e l l a r p r e c i p i t a t e , but in addition f r e e s u r f a c e s such as h o l e s in the s a m p l e , the s a m p l e s u r f a c e , e t c . , p r o v i d e nuc l e a t i o n s i t e s . The k i n e t i c s of the f i n e l y l a m e l l a r d i s c o n t i n u o u s p r e c i p i t a t i o n a r e i n v e s t i gated. The a p p l i c a b i l i t y of s e v e r a l m o d e l s f o r the d e s c r i p t i o n of d i s c o n t i n u o u s l a m e l l a r p r e c i p i t a t i o n is e x a m i n e d . The c r i t e r i o n of F o u r n e l l e and C l a r k is upheld f o r p r e c i p i t a t i o n in Cu-Sb s o l i d s o l u t i o n s .
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p r e v i o u s r e p o r t s x'2 it has b e e n shown that in the c a s e of F e - N i and F e - M n s o l i d s o l u t i o n s , s i m i l a r p r e c i p i t a t i o n b e h a v i o r is o b s e r v e d to o c c u r when the e q u i l i b r i u m s t a t e s in the r e l e v a n t r e g i o n of t e m p e r a t u r e and c o n c e n t r a t i o n a r e c o m p a r a b l e . A f t e r i n v e s t i g a t i o n s in C u - I n s o l i d s o l u t i o n s had b e e n c a r r i e d out, s'4 it b e c a m e e v i d e n t that the p r e c i p i t a t i o n b e h a v i o r of s u p e r s a t u r a t e d Cu-Sb s o l i d s o l u t i o n s should be c a r e f u l l y i n v e s t i g a t e d . M o r e o v e r it b e c a m e c l e a r that one should d e t e r m i n e w h e t h e r o r not in Cu-Sb s o l i d s o l u t i o n s a c o a r s e l y l a m e l l a r p r e c i p i t a t e o c c u r s in addition to a finely l a m e l l a r discontinuous precipitate. The e q u i l i b r i u m s i t u a t i o n p e r t i n e n t to the r e g i o n s of t e m p e r a t u r e and c o n c e n t r a t i o n in which the p r e c i p i t a tion has b e e n i n v e s t i g a t e d , is i l l u s t r a t e d in Fig. 1. 5-~ The a - s o l u b i l i t y line g i v e n by Hansen and A n der k o 5 has b e e n s u b s t a n t i a l l y c o n f i r m e d by the m e a s u r e m e n t s of R~tjda. 6 C o p p e r d i s s o l v e s a m a x i m u m of 6.0 at. pct Sb at 918 K. The s p h a s e p r e c i p i t a t e s out in the t e m p e r a t u r e r a n g e in which the p r e c i p i t a t i o n k i n e t i c s have b e e n fol l o wed . Its r a n g e of h o m o g e n e i t y is f r o m ~ 18.5 to 20.0 at. p c t Sb.
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