Thermodynamics of oxide-sulfate melts: The system PbO-PbSO4
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AGEbo = XP2b S O
4
{- 42,450 + 20,000 XpbSO4 } J mol-~
AGEbso, = )@bO { - 12,450 - 20,000 X p b o } J mo1-1 A G E = Xpb O X p b s o 4 {- 32,450 Xpb O - 22,450 X p b s o 4 } J tool -1.
The s t a n d a r d f r e e e n e r g y of f o r m a t i o n of liquid PbSO4 f r o m p u r e liquid PbO and g a s e o u s SO3 at 1 arm at 1253 K was e v a l u a t e d as - 8 8 . 0 2 (+0.72) kJ mo1-1.
THE t h e r m o d y n a m i c p r o p e r t i e s
of o x i d e - s u l f a t e m e l t s a r e not a v a i l a b l e in the l i t e r a t u r e . A c t i v i t i e s in o x i d e - c a r b o n a t e m e l t s (Ca(9 + CaCO3, BaO + BaCO3 and SrO + SrCO3) c o n t a i n i n g a c o m m o n c a t i o n have b e e n r e p o r t e d by B a k e r and R i c h a r d s o n t in the t e m p e r a t u r e r a n g e 1475 to 1775 K. D e s p i t e the s i g n i f i c a n t d i f f e r e n c e in the Size of the a n i o n s , t h e s e s o l u t i o n s a p p e a r to be r e g u l a r a c r o s s the l i m i t e d r a n g e of c o m p o s i t i o n a m e n a b l e to e x p e r i m e n t a l study. Negative deviations from Raoultian ideality become more p r o m i n e n t with i n c r e a s i n g s i z e of the c a t i o n s . Negative d e v i a t i o n s have also b e e n o b s e r v e d by F ~ r l a n d 2 in m e l t s of c a l c i u m c a r b o n a t e with a l k a l i m e t a l c a r b o n a t e s . The r e s u l t s a r e c o m p a t i b l e with the s i m p l e s t m i x i n g m o d e l in which the c a t i o n p o s i t i o n s m a y be occupied by m o n o - or d i v a l e n t ions without c o n s i d e r a tion of the r o l e of v a c a n c i e s in the e n t r o p y of m i x i n g . F ~ r l a n d 3 has also m e a s u r e d a c t i v i t i e s in the CaCOaNa2SO4 r e c i p r o c a l s y s t e m w h e r e m i x i n g of ions on both the anion and cation s u b l a t t i c e s o c c u r s . Melts with a c o m m o n c a t i o n and s i m p l e a n i o n s a r e u s u a l l y found to have s m a l l p o s i t i v e or n e g a t i v e heats or exces f r e e e n e r g i e s of m i x i n g . F o r e x a m p l e , the F e S - F e O m e l t is n e a r l y ideal. 4 The c h l o r i d e - b r o m i d e m e l t s s t u d i e d by T o g u r i , Flood and F f i r l a n d 5 have m a x i m u m v a l u e s for heat of m i x i n g at e q u i m o l a r c o m p o s i t i o n s , r a n g i n g f r o m +550 to - 1 7 0 J mo1-1. T h e r m o d y n a m i c c a l c u l a t i o n s by F l o o d e t a l 6 and L u m s d e n , 7 b a s e d on p h a s e d i a g r a m s , s u g g e s t that the Na2SO4NaC1 and Na2SO4-NaBr s y s t e m s a r e a p p r o x i m a t e l y ideal, while the KzSO4-KC1 s y s t e m has a m a x i m u m K. T. JACOB and J. M. TOGURI, are Assistant Professor, Chairman and Professor, respectively, with the Department of Metallurgy and Materials Science, University o f Toronto, Toronto, Canada, MSS 1A4. Manuscript submitted November 28, 1977. M E T A L L U R G I C A L TRANSACTIONS B
heat of m i x i n g of 210 J tool -1. The c h r o m a t e - d i c h r o m a t e m
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