On the dilute solutions of gold in Bi-Sn alloys
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The r e l a t i v e p a r t i a l g r a m - a t o m i c e n t h a l p y of gold AHAu at infinite dilution in b i s m u t h , tin, and six B i - S n a l l o y s has been m e a s u r e d at 623~ The c o m p o s i t i o n dependence (dA~rAu/dXAu)x.~u--o i n b i s m u t h and two B i - S n a l l o y s and the t e m p e r a t u r e coefficient (dAHAu,xAu--o)/dT in t h r e e B i - S n alloys have also b e e n m e a s u r e d . An a n a l y s i s of the r e s u l t s b a s e d on the q u a s i c h e m i c a l t h e o r y shows that (dAHAu/dXAu)xAu---*0 is v e r y s e n s i t i v e and AHAu,m~u~0 is i n s e n s i t i v e to n o n z e r o v a l u e s of the r e l a t i v e e n e r g y of s o l u t e - s o l u t e b o n d s ; t h e a n a l y s i s a l s o shows that a d e c r e a s e in the coo r d i n a t i o n n u m b e r has a s m a l l effect on (dAHAufdXAu)x~---.o, but has an a p p r e c i a b l e effect on AHAu,xAu-"O. T H E dilute s o l u t i o n s of gold in B i - S n a l l o y s do not behave in a s i m p l e m a n n e r w h e r e a s the b i n a r y B i - S n s o l u t i o n s a p p r o x i m a t e ideal b e h a v i o r . 1,2 V a l u e s of the r e l a t i v e p a r t i a l g r a m - a t o m i c enthalpy of gold at infinite dilution in s e v e r a l B i - S n a l l o y s 3 show s t r o n g n e g a t i v e deviations f r o m ideality. T h e s e r e s u l t s have b e e n explained by a change of the c o o r d i n a t i o n n u m b e r Z of gold in these s o l u t i o n s with the c o m p o s i t i o n of the solvent. In the i n v e s t i g a t i o n r e p o r t e d h e r e , the r e l a t i v e p a r t i a l g r a m - a t o m i c enthalpy of gold at infinite dilution and the dependence of the p a r t i a l g r a m - a t o m i c e n thalpy of gold on c o n c e n t r a t i o n and on t e m p e r a t u r e in v a r i o u s B i - S n alloys have b e e n m e a s u r e d . The r e s u l t s can be i n t e r p r e t e d in t e r m s of the bond e n e r g i e s and the c o o r d i n a t i o n n u m b e r a c c o r d i n g to a modified q u a s i c h e m i c a l theory. EXlaERIMENTAL B i s m u t h c o n t a i n i n g 0.003 pct Cu, 0.0002 pet As, and 0.0001 pct each of F e , Si, lab, and Mg, and tin cont a i n i n g 0.003 pct Zn, 0.002 pct lab, 0.0005 pct F e , 0.0003 pct Cu, and 0.00003 pct As were used. W i r e s of gold (0.003 pct Cu and 0.003 pct Ag) were a n n e a l e d u n d e r v a c u u m for 1 h r at 823~ The a n a l y s e s a r e those r e p o r t e d by the s u p p l i e r s . The heat effects of additions of gold to the s o l v e n t b a t h , which i n i t i a l l y was a B i - S n solution, were m e a s u r e d in a solution c a l o r i m e t e r d e s c r i b e d e l s e w h e r e . 4 B i s m u t h and tin were m e l t e d together in the c a l o r i m e t e r in o r d e r to p r e p a r e a s o l v e n t bath (approximately 3.1 g - a t o m ) of the d e s i r e d c o m p o s i t i o n . The c a l o r i m e t e r was c a l i b r a t e d by adding a m i x t u r e of b i s m u t h and t i n which had the s a m e r
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