EMF and calorimetric measurements on the Mg-In liquid solutions
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MOSER
AND
ROBERT
CASTANET
By m e a n s of c o n c e n t r a t i o n c e l l s : Mg (s)lMgClz (LiC1)KC1)eu t (/){Mg-In (1) p a r t i a l m o l a r t h e r m o d y n a m i c d a t a of Mg in M g - I n liquid a l l o y s have b e e n d e t e r m i n e d in the c o m p o s i t i o n r a n g e 0.03 -< XMg --< 0.6 and at t e m p e r a t u r e s 770 to 890 K. I n t e g r a l m o l a r e n t h a l p i e s m e a s u r e d in a C a l v e t c a l o r i m e t e r at 948 and 1008 K w e r e u s e d f o r c a l c u l a t i o n of the p a r t i a l m o l a r e n t h a l p y of m a g n e s i u m , AHMg. V a l u e s of s with p a r t i a l m o l a r f r e e e n e r g i e s of Mg f r o m e m f s t u d i e s w e r e u s e d f o r d e r i v a t i o n of p a r t i a l molar excess entropies.
IN the
t h e r m o d y n a m i c s of a l l o y s both e m f and c a l o r i m e t r i c m e t h o d s a r e c o m m o n l y u s e d . E a c h of t h e s e m e t h o d s r e s u l t s in e x p e r i m e n t a l t h e r m o d y n a m i c d a t a which a r e e m p l o y e d for f u r t h e r c a l c u l a t i o n s a p p l y i n g the G i b b s - D u h e m equation. It was shown that with the e m f method p a r t i a l t h e r m o d y n a m i c functions of the l e s s noble c o m p o n e n t a r e of s p e c i a l i m p o r t a n c e while the c a l o r i m e t r i c technique g i v e s the e x a c t v a l u e s of enthalpies. The a i m of our p r e v i o u s emf i n v e s t i g a t i o n s on b i n a r y m a g n e s i u m a l l o y s ~'4 w a s to d e t e r m i n e the p a r t i a l m o l a r t h e r m o d y n a m i c functions of m a g n e s i u m , to c a l c u l a t e the f r e e e n e r g y of f o r m a t i o n of i n t e r m e t a l l i c c o m p o u n d s and to a p p l y v a r i o u s m e t h o d s in the i n t e r p r e t a t i o n of e x p e r i m e n t a l d a t a . It was shown that p a r t i a l m o l a r e n t r o p i e s and e n t h a l p i e s c a l c u l a t e d f r o m t e m p e r a t u r e c o e f f i c i e n t s a r e a c c o m p a n i e d by c o n s i d e r a b l e e r r o r . It was t h e r e f o r e d e c i d e d to c o m b i n e e m f and c a l o r i m e t r i c m e t h o d s in one s t u d y . The a i m of the p r e s e n t r e s e a r c h was to d e t e r m i n e t h e r m o d y n a m i c functions for liquid M g - l n s o l u t i o n s by emf and c a l o r i m e t r i c t e c h n i q u e s , to a n a l y z e the a c c u r a c y of t h e r m o d y n a m i c d a t a o b t a i n e d b y e a c h method and to use s e l e c t e d v a l u e s f o r c a l c u l a t i o n of the e x c e s s p a r t i a l m o l a r e n t r o p y of m a g n e s i u m . The obtained r e s u l t s w e r e c o m p a r e d with a v a i l a b l e p u b l i s h e d d a t a and m a y be u s e d f o r c a l c u l a t i o n of i n t e r a c t i o n p a r a m e t e r s and the p h a s e d i a g r a m .
E m f d a t a w e r e obtained with c e l l s of the type: [1]
in the c o n c e n t r a t i o n r a n g e of m a g n e s i u m in m o l a r f r a c t i o
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