A note on the solubility of graphite in Bcc iron
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A Note on the Solubility of Graphite in Bcc Iron R E X B. M c L E L L A N AND WILLIAM W. DUNN A fundamental t h e r m o d y n a m i c quantity, the p a r t i a l f r e e e n e r g y of a c a r b o n atom in b c c i r o n , has r e c e n t l y b e e n the s u b j e c t of much d i s c u s s i o n and i n v e s t i g a t i o n . The m o t i v a t i o n f o r much of this w o r k is the l a r g e d i s c r e p a n c y e x i s t i n g b e t w e e n the v a l u e s found for the heat of solution of c e m e n t i t e in f e r r i t e by a n e l a s t i c d a m p i n g m e t h o d s , ~-3 9.7 k c a l p e r m o l e , and the v al u e of 15 keal p e r m o l e c a l c u l a t e d f r o m the f o r m a t i o n e n e r g y of e e m e n t i t e and the g r a p h i t e s o l u b i l i t y data of smith.4 Smith 4 m e a s u r e d the e q u i l i b r i u m b e t w e e n f e r r i t e and CH4-H2 m i x t u r e s at 750 ~ and 800~ An a n a l y s i s of his data 5 y i e l d s a r e l a t i v e p a r t i a l e n e r g y of g r a p h i t e in f e r r i t e of 20.2 k c a l p e r m o l e and a p a r t i a l e x c e s s e n t r o p y of S V / k = 5.2. E a r l i e r , Dfinnwald and Wagn e r 6 had m e a s u r e d the e q u i l i b r i u m b e t w e e n CO-CO2 gas m i x t u r e s and f e r r i t e but only at one t e m p e r a t u r e . H o w e v e r , the ~v c a l c u l a t e d ~ f r o m Dfinnwald and Wagn e r ' s data using the AHc taken f r o m S m i t h ' s data a g r e e s welt with that c a l c u l a t e d f r o m S m i t h ' s data alone. T h u s , it a p p e a r s that t h e s e two s e t s of data are compatible. Swartz 7 p r e s e n t e d an e x p l a n a t i o n f o r the d i s c r e p a n c y b e t w e e n the e x p e r i m e n t a l l y d e t e r m i n e d c e m e n t i t e s o l u b i l i t y in f e r r i t e and that c a l c u l a t e d f r o m the Smith and Dfinnwald and W a g n e r data b a s e d on the e f f e c t s of p r e cipitation s t r e s s e s on the s o l u b i l i t y of e e m e n t i t e p r e c i p i t a t e s in f e r r i t e . Much of the d i s c r e p a n c y was r e m o v e d by this m e a n s and the r e m a i n i n g d i s a g r e e m e n t has been a c c o u n t e d f o r e v e n f u r t h e r by S w a r t z ' s r e c e n t d e t e r m i n a t i o n of the g r a p h i t e s o l u b i l i t y in bcc i r o n . ~ In this work Swartz m e a s u r e d the e q u i l i b r i u m b e t w e e n f e r r i t e and a v a r i e t y of d i f f e r e n t g a s m i x t u r e s . The c a r b o n a n a l y s i s of the i r o n was d e t e r m i n e d by m e a s u r i n g the height of the Snoek p e a k s of the e q u i l i b r a t e d s a m p l e s . The c o n s t a n t s of p r o p o r t i o n a l i t y r e l a t i n g the Snoek peak height to the c a r b o n c o n c e n t r a t i o n w e r e d e r i v e d f r o m r e s u l t s obtained in the v i c i n i t y of 1000~ using c o m b u s t i o n a n a l y s i s . The solubility data of Swartz 7 y i e l d s a value of 24.0 k c a l p e r m o l e for A H c , c o n s i d e r a b l
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