Thermodynamic properties of Pr-Zn alloys
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A~'---XSzn = N2Pr [a +
bNzn + CNzn2 + dNzn + eN4zn + fNzn5 ]
f r o m which the r e l a t i o n
AFXSpc = N ' 2 z n [ a + b ( N z n --1) + CNzn (Nzn - 2) + dNzn (Nzn - ~) + eNzn (Nzn - 4) + f/~Zn ( N z n - ~ ) I w a s o b t a i n e d by i n t e g r a t i o n of the G i b b s - D u h e m equation. In t h e s e r e l a t i o n s N is the a t o m f r a c t i o n , a = - 1 6 , 2 5 0 + 4.00T, b = - 3 0 , 6 5 0 + l l . 5 0 T , c = 15,290 - 30.17 T, d = - 1 5 3 , 0 0 0 + 70.0T, e = 9000 + 20.0T, f = 9000 + 20.0T. The s t a n d a r d f r e e e n e r g y c h a n g e s for the reactions Pr(ot) + x Z n ( / ) ~ P r Z n x ( S ) are AF~
n) = - 1 7 , 2 1 0 + 3.80 T,
AF~
= - 3 8 , 5 8 0 + 12.34
AF~
~F~
T,
= - 5 1 , 2 0 0 + 18.75T,
AF~
= - 8 0 , 3 4 0 + 36.65T,
= --44,600 + 15.30 T ,
zxF~
= - 7 2 , 8 3 0 + 31.72T,
AF~
= -85,300 + 42.7T
[1]
for the s t a n d a r d f r e e e n e r g y of f o r m a t i o n of the solid compound f r o m solid a l p h a - p r a s e o d y m i u m and liquid z i n c . The s o l u b i l i t y of p r a s e o d y m i u m in liquid zinc for the t e m p e r a t u r e r a n g e 425 ~ to 725~ log Npr = 4.268 - 6591/T
[2]
has b e e n r e p o r t e d by J o h n s o n and D i l l o n . s In t h e s e r e l a t i o n s T i s in d e g r e e s K e l v i n and N is the atom f r a c t i o n . T h e s e r e l a t i o n s p e r m i t a 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 l f r e e e n e r g y of p r a s e o d y m i u m in the z i n c - r i c h liquid, o r ~F~rS : - 5 5 , 1 0 0
+
23.1T
[3]
The p u r p o s e of this i n v e s t i g a t i o n was to m e a s u r e P. CHIOTTI is Senior Metallurgist,Ames Laboratory of the U. S. Atomic Energy Commission, and Professor of Metallurgy, Iowa State University, Ames, Iowa. J. T. MASON is Assistant Metallurgist, Ames Laboratory of the U. S. Atomic Energy Commission, Ames, Iowa. Manuscript submitted September 14, 1970. METALLURGICALTRANSACTIONS
T,
~xF~
T H E phase d i a g r a m for the P r - Z n s y s t e m has b e e n r e p o r t e d 1 and eight c o m p o u n d s , P r Z n , P r Z n 2 , P r Z n 3 , PrZns.87, PrZn4.4e, PrZnT.33, PrZns.s, and PrZn1~, have been identified. The phase relations and crystal structures of these compounds are well established but data on the thermodynamic properties for these c o m pounds and liquid P r - Z n alloys is meager. Johnson and Yonco z have employed a fused salt cell to measure the electromotive force between praseodymium m e t a l and liquid zinc s a t u r a t e d with the compound P r Z n l x . F r o m t h e s e data they o b t a i n e d a r e l a t i o n AF~
= - 2 9 , 1 6 0 + 7.56
= - 8 9 , 3 5 0 + 45.48T.
the zinc v a p o r p r e s s u r e s o v e r solid and liquid a l l o y s and to e m p l o y t h e s e data to c a l c u l a t e t h e i r t h e r m o dynamic properties. EXPERIMENTAL Materials The m a t e r i a l s used in this i n v e s t i g a t i o n w e r e B u n k e r H i l l s l a b z i n c , 99.99 pct p u r e and A m e s L a b o r a t o r y p r a s e o d y m i u m m e t a l c o n t
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