Thermodynamic measurements in liquid copper-tin alloys
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Thermodynamic Measurements in Liquid Copper-Tin Alloys A. K. SENGUPTA, K. P. JAGANNATHAN, AND A. GHOSH T h e r e v e r s i b l e galvanic cell, Sn(/), S n O 2 ( S ) / C a l c i a - s t a b i l i z e d / C u - S n ( l ) , Zirconia
SnO2(S)
[I]
was employed to d e t e r m i n e activity and p a r t i a l f r e e e n e r g y of mixing of tin in m o l t e n c o p p e r - t i n alloys at 800~ (1073 K) in the c o m p o s i t i o n r a n g e , 0.2 -< XSn 0.7 v a l u e s of ~Sn taken for G i b b s D u h e m i n t e g r a t i o n w e r e those e x t r a p o l a t e d following the b e h a v i o r of aSn vs XSn c u r v e at Xsn < 0.7. T h i s follows a s u g g e s t i o n made by D a r k e n . s All r e l e v a n t data a r e p r e s e n t e d in T a b l e I along with an u n c e r t a i n t y a n a l y s i s at XSn = 0.5. T h e e x p e r i m e n t a l v a l u e s of asn y i e l d a s m o o t h c u r v e when plotted as function of XSn (Fig. 1). F u r t h e r m o r e
I I I I
i -0.2 ]
-0-8 t-
"6
t
-0.q
-0.1
t~
o
-0.6
-0.8
-0.: O
-1.0
0.2
I 0.2
t
-1.2
I
0.6
1.0
Xsn Fig. 2--Alpha function for tin at 1073 K in molten copper-tin system; dotted portions are extrapolated. 142-VOLUME 9B, MARCH 1978
o
o12
0.6 o.8 1.0 ( 1 Xsn) 2 - - - - . Fig. 3--log ~Sn vs (1 - XSn)2 in molten Cu-Sn system at 1073 K. 9 value arrived at on the basis of extrapolated c~-function. -
METALLURGICALTRANSACTIONS B
Table I. Data on Molten Cu-Sn System at 1073 K
XSn
emf, mV
asn
acu*
(J/g mole)t
ash (Calculated from Selected Values6)
asn (Ref. 8)
0.1 0.2 0.3
66.90 35.65
0.007 0.055 0.214
0.858 0.600 0.386
-5,602 -8,755 -10,011
0.004 0.058 0.202
0.137
0.4 0.5
24.04 17.25
0.296 0.240
-9,467 -9,190
0.367 0.503
0.6 0.7 0.8 0.9
12.80 8.80 5.00 2.35
0.353 0.474 (-+0.007) 0.575 0.683 0.805 0.903
0.182 0.133 0.086 0.040
-8,491 -7,373 -5,669 -3,479
0.613 0.705 0.799 0.897
AG M
(at Xsn = 0.35) 0.501 0.839 0.949
*Reportedvaluesof acu are with respect to pure liquidcopper as the standard state. The valuesshould be multipliedby 1.34 if pure solidcopper is taken as the standard state. "{'AGMis integralmolalfreeenergy of mixingwith pure liquidsas standard state.
the c u r v e m e r g e s with the R a o u l t ' s Law line at XSn > 0.8. T h e s e e s t a b l i s h the g e n e r a l r e l i a b i l i t y of the data. T h e s y s t e m e x h i b i t s a s t r o n g n e g a t i v e d e v i a t i o n f r o m the R a o u l t ' s L a w line indicating s t r o n g i n t e r a c t i o n b e t w e e n c o p p e r and tin a t o m s . V a l u e s of asn of this study w e r e c o m p a r e d with t h o s e c a l c u l a t e d f r o m the s e l e c t e d v a l u e s of H Sn M and SMn.6 T h e s e a r e p r e s e n t e d in T a b l e I. It is s e e n that the d i s a g r e e m e n t is l e s s than 5 pct. F i g u r e 3 shows the plot of log 7Sn v s (1 - X S n ) 2. F r o m this f i g u r e it a p p e a r s that the solution b e h a v e s in a s i m p l e m a n n e r in the two e x t r e m e s but b e h a v e s in a c o m p l i c a t e d
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