The liquidus surface and tie-lines in the iron-nickel-sulfur system between 1473 and 1673 K
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B. R. CONARD,
R. SRIDHAR,
AND
J. S. WARNER
T h e liquidus c o m p o s i t i o n s and the t i e - l i n e s for the s o l i d a l l o y p l u s liquid s u l f i d e twop h a s e r e g i o n w e r e d e t e r m i n e d for the i r o n - n i c k e l - s u l f u r s y s t e m in the t e m p e r a t u r e r a n g e 1473 to 1673 K. E x p e r i m e n t s w e r e c o n d u c t e d by s a m p l i n g the liquid s u l f i d e in e q u i l i b r i u m with the a l l o y p h a s e and c h e m i c a l l y a n a l y z i n g the s u l f i d e . T h e a l l o y w a s q u e n c h e d and a n a l y z e d by e l e c t r o n m i c r o p r o b e . T h e r e s u l t s r e p r e s e n t a s i g n i f i c a n t r e v i s i o n to e x i s t i n g d a t a .
DESPITEthe
i m p o r t a n c e of the F e - N i - S s y s t e m for the p y r o m e t a l l u r g i c a l e x t r a c t i o n of n i c k e l f r o m i t s ores, little thermodynamic data has been published for t e m p e r a t u r e s above 1300 K. D i f f e r e n t v e r s i o n s of the p h a s e d i a g r a m at high t e m p e r a t u r e s w e r e r e p o r t e d by V o g e l and Tonn I and by U r a z o v and F i l i n , 2 both of whom u s e d t h e r m a l a r r e s t t e c h n i q u e s to d e t e r m i n e the t e r n a r y l i q u i d u s . M o r e r e c e n t l y , Vanyukov e t al 3 d e t e r m i n e d the liquidus b y DTA, but t h e r e s t i l l e x i s t e d s u b s t a n t i a l d i s a g r e e m e n t b e t w e e n the r e p o r t e d liquidus temperatures. The phase relations for temperatures up to 1373 K w e r e r e p o r t e d b y K u l l e r u d and c o w o r k e r s , 4 who s t u d i e d the s y s t e m u s i n g q u e n c h i n g e x p e r i m e n t s , high t e m p e r a t u r e X - r a y d i f f r a c t i o n and D T A . A c t i v i t i e s of c o m p o n e n t s in n i c k e l - i r o n m a t t e s have b e e n m e a s u r e d by V a i s b u r d ~ u s i n g E M F c o n c e n t r a t i o n c e l l s and by B y e r l e y and T a k e b e 8 and M e y e r 7 u s i n g H2S/H2 gas p h a s e e q u i l i b r a t i o n o v e r the t e m p e r a t u r e r a n g e of 1473 to 1673 K. M e y e r ' s m e a s u r e m e n t s a r e the m o s t r e l i a b l e to d a t e but the l a c k of a c c u r a t e a c t i v i t y d a t a for s o l i d n i c k e l - i r o n a l l o y s at t h e s e t e m p e r a t u r e s and the l a c k of good t i e - l i n e and liquidus i n f o r m a t i o n r e s t r i c t e d h i m to r e l a t i n g i r o n and n i c k e l a c t i v i t i e s in the m e l t s to a r b i t r a r y s t a n d a r d s t a t e s . The o b j e c t i v e of the p r e s e n t w o r k was to d e t e r m i n e p h a s e r e l a t i o n s b e t w e e n a l l o y and s u l f i d e at t e m p e r a t u r e s f r o m 1473 to 1673 K. T h e s e r e s u l t s , t o g e t h e r with M e y e r ' s d a t a and the i r o n and n i c k e l a c t i v i t i e s for the s o l i d a l l o y r e p o r t e d by C o n a r d e t a l , 8 c a n be u s e d to d e r i v e i r o n and n i c k e l a
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