The thermodynamic properties of dilute solutions of oxygen in the liquid Fe-Ni-Co alloys
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A knowledge of the t h e r m o d y n a m i c b e h a v i o r of dilute s o l u t i o n s of oxygen in liquid m e t a l s and a l l o y s is of i m p o r t a n c e in f u r t h e r i n g our u n d e r s t a n d i n g of the physical c h e m i s t r y of m e t a l l u r g i c a l r e f i n i n g and a l l o y m a k ing p r o c e s s e s . The b e h a v i o r of oxygen in the t e r n a r y s y s t e m F e - N i - C o is d e s c r i b e d in this p a p e r . Most of the r e p o r t e d i n v e s t i g a t i o n s have b e e n on s y s t e m s b a s e d upon dilute alloys of iron. G e n e r a l l y , t h e s e s t u d i e s have b e e n on the effect of additions of a t h i r d e l e m e n t on the a c t i v i t y of oxygen in i r o n . T h i s work has b e e n a s s e s s e d and r e v i e w e d by E l l i o t t e t a l . 1 The effect of s m a l l a d d i t i o n s of a t h i r d e l e m e n t is m o s t c o n v e n i e n t l y d e s c r i b e d by m e a n s of the i n t e r a c tion p a r a m e t e r d e v i s e d b y Wagner 2 but g r a p h i c a l or n u m e r i c a l r e p r e s e n t a t i o n of the i n t e r a c t i o n i s n e e d e d for m o r e complex s y s t e m s or when the c o n c e n t r a t i o n of the t h i r d e l e m e n t e x c e e d s a few per cent. The p r e s e n t author 3 has p r e s e n t e d data on dilute solution of oxygen in the liquid b i n a r y m e t a l s y s t e m s F e - N i , F e - C o , and N i - C o a c r o s s the full r a n g e of m e t a l c o m p o s i t i o n . R e c a l c u l a t e d c u r v e s showing the s t a n d a r d Gibbs e n e r g y of solution of oxygen for the t h r e e b i n a r y m e t a l s y s t e m s at 1550~ a r e shown in F i g . 1. The s t a n d a r d state of the oxygen in s o l u t i o n has b e e n changed f r o m 1 wt to 1 at. pct, the r e f e r e n c e state b e i n g the i n f i n i t e l y dilute solution. In the e a r l i e r work, s e x p e r i m e n t a l e v i d e n c e was p r e s e n t e d which s u g g e s t e d that the heat of solution of oxygen r e m a i n e d s u b s t a n t i a l l y the s a m e as that in pure i r o n up to at least 20 at. pct of Ni or Co. As a c o n s e quence of this, heats of solution have b e e n d e t e r m i n e d along one b i n a r y s e c t i o n of the t e r n a r y m e t a l s y s t e m .
equilibrium furnace. T e m p e r a t u r e s were measured by m e a n s of a c a l i b r a t e d optical p y r o m e t e r sighted through an optical flat onto the c r u c i b l e p e d e s t a l and by m e a n s of a P t - P t 10 pct Rh t h e r m o c o u p l e i n s e r t e d in the s u p p o r t tube of the c r u c i b l e p e d e s t a l . It h a s b e e n shown e a r l i e r 4 in the work on i r o n , cob a l t , and n i c k e l that e q u i l i b r i u m was effectively
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I 40
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I 60
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Ni
At %Ni
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Co/N] = 1
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Co/N] = 2 77.7 Fe 71.0 Fe 63,7 Fe 63.7 Fe 41.2 Fe 25.9 Fe 14.9 Fe 14.9 Fe 14.9 Fe 14.9
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