On the rate limiting step in the decarburization of iron droplets in an oxidizing slag
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(J/mole).
+0.837
[71 A s s u m i n g that the heats of m e l t i n g of t i n (7029 J / g 9atom) and t e l l u r i u m (17,489 J / g . a t o m ) a r e t e m p e r a t u r e independent and that ACp ~-- 0 for the f o r m a t i o n of SnTe, which is s u p p o r t e d by the e v a l u a t e d data, Ix one m a y w r i t e , s t a r t i n g with Eq. [71, for the f o r m a t i o n of SnTe f r o m liquid tin and liquid t e l l u r i u m a c c o r d i n g to the r e a c t i o n : Sn(/) + T e ( / ) = SnTe(s) ~G~nTe (s)
= - 8 5 , 1 0 2 + 36.71T J / m o l e .
[9]
As the a c t i v i t y of tin in SnTe (in contact with tin oxide) is v e r y s m a l l , Eq. [9] will be pushed in the d i r e c t i o n r i g h t to left. M o r e o v e r , it has b e e n pointed out by Shunk x4 that SnO d i s p r o p o r t i o n a t e s to Sn and SnO2 at ~175~ The a s s u m p t i o n of unit a c t i v i t y of SnO2 is, therefore, justified. The f r e e e n e r g y of f o r m a t i o n of the compound SnTe can be c a l c u l a t e d f r o m the e q u i l i b r i u m d i a g r a m applying J o r d a n ' s r e g u l a r a s s o c i a t e d s o l u t i o n s model. ~2 T a k i n g the heat and e n t r o p y of fusion of SnTe data f r o m B a r i n , Knacke and K u b a s c h e w s k i ' s c o m p i l a t i o n ~~ and the liquidus of the e q u i l i b r i u m d i a g r a m of the SnT e s y s t e m f r o m H a n s e n , ~s'14 one o b t a i n s a value of -32,635 J for the free e n e r g y of f o r m a t i o n of one mole of Sno.sTeo.5 at its m e l t i n g point f r o m liquid tin and t e l l u r i u m . T h i s value is s m a l l e r than the one obtained f r o m Eq. [6]. The d i f f e r e n c e is p o s s i b l y due to the a s s u m p t i o n s and a p p r o x i m a t i o n s involved in J o r d a n ' s mode 1. The a u t h o r s a r e g r a t e f u l to P r o f e s s o r S. L. 118
V O L U M E 10B, M A R C H 1979
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Selected Values of the Thermodynamic Properties of Binary Alloys, pp. 1325-28, ASM, Metals Park
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