Thermodynamic properties of magnesium-lead alloys
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s e e k i n g s o l u t i o n s to the G i b b s - D u h e m equation for the p u r p o s e of d e s c r i b i n g the t h e r m o d y n a m i c p r o p e r t i e s of m e t a l l i c s o l u t i o n s , Krupkowski I p r o posed e m p i r i c a l a n a l y t i c a l f o r m s for g e n e r a l i z e d r e p r e s e n t a t i o n s of the l o g a r i t h m s of activity coeffic i e n t s as functions of t e m p e r a t u r e and composition. F o r a b i n a r y s y s t e m this approach allows e x p e r i m e n tal data for a l i m i t e d t e m p e r a t u r e and c o m p o s i t i o n r a n g e to be e x t r a p o l a t e d o v e r the complete c o m p o s i tion r a n g e and over an e x t e n s i v e t e m p e r a t u r e r a n g e . The r e a d e r is r e f e r r e d to p r e v i o u s work 2-7 by one of the authors (ZM) d i s c u s s i n g the a p p l i c a t i o n s of K r u p kowski's formulae. It has been found that for b i n a r y s y s t e m s exhibiting positive d e v i a t i o n s f r o m R a o u l t ' s law the f o r m u l a e a r e capable of a d e q u a t e l y d e s c r i b i n g t h e r m o d y n a m i c b e havior over the c o m p l e t e c o m p o s i t i o n r a n g e . However, in t e s t i n g the a p p l i c a b i l i t y of the f o r m u l a e to s y s t e m s exhibiting negative d e v i a t i o n s f r o m R a o u l t ' s law, it has b e e n found that adequate d e s c r i p t i o n s of b e h a v i o r a r e attainable for s y s t e m s where the s t r e n g t h s of i n t e r a c t i o n a r e r e l a t i v e l y weak ( e . g . the M g - Z n 5 and Mg-Sn s s y s t e m s ) , but the f o r m u l a e a r e inadequate for d e s c r i p t i o n of the b e h a v i o r of s y s t e m s exhibiting s t r o n g negative i n t e r a c t i o n s ( e . g . the Mg-Bi and MgSb systemsT). The Mg-Pb s y s t e m exhibits negative i n t e r a c t i o n s , and the p r e s e n t p a p e r s u m m a r i z e s a study of this s y s t e m . The phase d i a g r a m of Eldridge et al s is shown in Fig. 1. Two i n t e r m e d i a t e phases a r e i n d i cated. One of these is cubic, Mg2Pb, and the other has a composition 0.5 to 1.7 at. pct r i c h e r in lead than Mg2Pb. PROCEDURE AND RESULTS E l e c t r o m o t i v e force (EMF) data w e r e taken o v e r the t e m p e r a t u r e r a n g e 745 to 868 K with c e l l s of the type Mg (s) I MgC12 in Li C1- KC1 (l) I Mg- Pb( l ) with Mg-Pb alloys having mole f r a c t i o n s 0.03 < XMg < 0.50. The e x p e r i m e n t a l a r r a n g e m e n t and c o n s t r u c Z. MOSER is Associate Professor, Institute for Metal Research, Polish Academy of Sciences, Krak6w, Reymonta 25, Poland. J. F SMITH is Professor, Dept. of Metallurgy, Iowa State University and Senior Metallurgist,Ames Laboratory of the U.S. Energy Resources Development Agency,Ames, Iowa 50010. Manuscript submitted November 18, 1974. METALLURGICAL TRANSACTIONS B
tion of the cell was e s s e n t i a l l y the s a m e as in p r e v i ous work. 5 Magnesium and lead of 99.99 pct p u r i t y w e r e used to m
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