Activity measurements in dilute Cu-Zn solutions
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A t o m i c a b s o r p t i o n s p e c t r o s c o p y h a s b e e n u s e d to m e a s u r e zinc p a r t i a l v a p o r p r e s s u r e s as functions of t e m p e r a t u r e f o r s e v e n C u - Z n alloys of zinc co n t en t r a n g i n g f r o m 0.0042 to 2.749 at. p c t Zn. F r o m the data, e x p r e s s i o n s have been d e r i v e d f o r the t h e r m o d y n a m i c a c t i v i t i e s and a c t i v i t y c o e f f i c i e n t s of zinc in t h e s e a l l o y s . At s e l e c t e d constant t e m p e r a t u r e s f r o m 769 to 1110 K, the zinc a c t i v i t y c o e f f i c i e n t s w e r e found to be i n v a r i a n t with r e s p e c t to a ll o y c o m p o s i t i o n . H e n c e , the e x p e r i m e n t a l data follow H e n r y ' s Law in the C u - Z n s y s t e m o v e r the r a n g e of zinc c o n c e n t r a t i o n s studied. The p a r t i a l enthatpy of s o lution of zinc at t h e s e low c o n c e n t r a t i o n s w as found to be - 5 9 1 0 + 200 c a l p e r g - a t o m r e f e r r e d to s o l i d z i n c .
T H E R E a r e v e r y few t e c h n i q u e s that p e r m i t the a c c u r a t e d e t e r m i n a t i o n of t h e r m o d y n a m i c a c t i v i t i e s of dilute s o l u t e s in m e t a l l i c s y s t e m s . This w o r k i n v e s t i g a t e s the s u i t a b i l i t y of one such t e c h n i q u e - - a t o m i c a b s o r p tion s p e c t r o s c o p y in s t a t i c o p t i c a l c e l l s - - a n d d e m o n s t r a t e s i t s c a p a b i l i t i e s in a t y p i c a l s y s t e m . Th e d e t a i l s of the t h e o r y and a d e s c r i p t i o n of the a p p a r a t u s h a v e been p r e s e n t e d e l s e w h e r e , 1-4 and need only be s u m m a r i z e d in this p a p e r . The h e a r t of the t e c h n i q u e is the r e s o n a n t a b s o r p tion of r a d i a t i o n f r o m a hollow cathode l a m p within an e v a c u a t e d and s e a l e d s i l i c a a b s o r p t i o n c e l l c o n t a i n i n g an alloy, one of whose c o n s t i t u e n t s is the s a m e as the e l e m e n t a c t i n g as the r a d i a t i o n s o u r c e . M e a s u r e m e n t of the a b s o r p t i o n of this r e s o n a n t r a d i a t i o n as a f u n c tion of t e m p e r a t u r e p r o v i d e s the t h e r m o d y n a m i c i n f o r m a t i o n d e s i r e d . The m o r e dilute an alloy is with r e s p e c t to the g i v e n e l e m e n t , the h i g h e r m u s t be the t e m p e r a t u r e of the a b s o r p t i o n c e l l to p r o v i d e m e a s u r a b l e r a d i a t i o n a t t e n u a t i o n . Thus the a c c u r a c y of the techniclue does not n e c e s s a r i l y d i m i n i s h as the s o l u t e c o n c e n t r a t i o n f a l l s , p r o v i d i n g one can e x p e r i m e n t a l l y c o n t r o l the t e m p e r a t u r e and avoid c h e m i c a l i n t e r a c t i o n with the o p t i c a l windows. M A T E R I A L S AND S P E C I M E N P R E P A R A T I O N The a l l o y s used in this study m a y be d iv id
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