Equilibrium relations in the system nickel oxide-copper oxide
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D E S P I T E t h e i r s i g n i f i c a n c e in p y r o m e t a l l u r g i c a l o p e r a t i o n s the i n f o r m a t i o n a v a i l a b l e about e q u i l i b r i u m r e l a t i o n s in the s y s t e m n i c k e l o x i d e - c o p p e r oxide is r a t h e r s c a r c e . T h e r m o c h e m i c a l p r o p e r t i e s of tile copper-oxygen system received considerable research i n t e r e s t owing to t h e i r i m p o r t a n c e in copper technology. P h a s e d i a g r a m for this s y s t e m , c o m p i l e d e a r l i e r by H a n s e n and A n d e r k o , 1 was modified by J o h n s o n and R h i n e s 2 in a c c o r d a n c e with the new liquidus data g e n e r a t e d in e m f m e a s u r e m e n t s of J a c o b , 3 G e r l a c h e t a l , 4 and O s t e r w a l d . 5 More r e c e n t l y , S a n t a n d e r and K u b a s c h e w s k i 6 r e v i s e d the s y s t e m on the b a s i s of a thorough a n a l y s i s of the a v a i l a b l e t h e r m o d y n a m i c data. The new d i a g r a m s 2,6 c o n t a i n e s s e n t i a l l y the s a m e feat u r e s except that p a r t i c u l a r l y in the c o m p o s i t i o n r a n g e Cu20-CuO, r e l e v a n t to the p r e s e n t study, c r i t i c a l t e m p e r a t u r e s s e l e c t e d by S a n t a n d e r and K u b a s c h e w s k i 6 a r e lower. In addition, the a r g u m e n t that C u 2 0 should have a n a r r o w r a n g e of h o m o g e n e i t y6 as opposed to the e s t i mate 2 of a s i z a b l e solid s o l u b i l i t y of CuO in Cu20 at t e m p e r a t u r e s > 1000~ is s u p p o r t e d by the r e s u l t s of n o n s t o i c h i o m e t r y m e a s u r e m e n t s of O'Keeffe and Moore 7 and t h e r m o g r a v i m e t r i c s t u d i e s of White e t a l . ~ However, J o h n s o n and Rhines 2 do not intend that the s o l u b i l i t y is definite as i n d i c a t e d by t h e i r b r o k e n boundary curve. Schmahl and Mfiller 9 e x a m i n e d the solid s t a t e r e a c tions b e t w e e n NiO and CuO; they r e p o r t e d a c o n s i d e r able s o l u b i l i t y of CuO in NiO but none of NiO in CuO, the a m o u n t of CuO d i s s o l v e d in NiO at a g i v e n t e m p e r a t u r e depended c r i t i c a l l y on the oxygen p a r t i a l p r e s s u r e . N e s t l e r 1~ c o n s t r u c t e d a q u a s i b i n a r y phase d i a g r a m for the s y s t e m NiO-Cu20 f r o m D T A data obtained upon cooling liquid NiO-Cu20 m i x t u r e s u n d e r a n e u t r a l a t m o s p h e r e . A e u t e c t i c r e a c t i o n was o b s e r v e d in this s y s t e m at 1218~ and 3.9 mol pct NiO, the two end m e m b e r s had no m u t u a l solid s o l u b i l i t y . A n e x a m i n a t i o n of N e s t l e r ' s data ~~ r e v e a l s the e x i s t e n c e of Cu or CuO in a m a j o r i t y of DTA s a m p l e s , i n d i c a t i n g that r a t h e r undefined oxygen p a r t i a l p r e s s u r e s e x i s t e d d u r i n g t h e i r m e a s u r e m e n t s . P r e s e n t work was u n d e r t a k e n to e s t a b l i s h the e q
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