The determination of oxygen in gas mixtures by electromotive force measurements using solid oxide electrolytes
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O N E of the most i m p o r t a n t a p p l i c a t i o n s of o x y g e n - i o n conducting solid e l e c t r o l y t e s is the d i r e c t d e t e r m i n a t i o n of the p a r t i a l p r e s s u r e of oxygen in gas m i x t u r e s at high t e m p e r a t u r e s . The oxygen c o n c e n t r a t i o n cell or oxygen probe, d e s c r i b e d by Littlewood, 1 can be used to c o n t r o l m a n y m e t a l l u r g i c a l p r o c e s s e s , e.g., c a r b u r i z ing, 2'3 a n n e a l i n g ,3'4 and c o m b u s t i o n , s The cell has a v i r t u a l l y i n s t a n t a n e o u s r e s p o n s e , can m o n i t o r oxygen p r e s s u r e s continuously, i s g e n e r a l l y c h e m i c a l l y i n e r t , can be reaOily used to t e m p e r a t u r e s in e x c e s s of 1600~ and can be used to m e a s u r e low oxygen p r e s s u r e s . However, oxide e l e c t r o l y t e s have only f a i r t h e r m a l shock r e s i s t a n c e , low ionic c o n d u c t i v i t i e s which help r e s t r i c t their use at low t e m p e r a t u r e s and, in some c a s e s , a s i g n i f i c a n t a m o u n t of e l e c t r o n i c conductivity at very low oxygen p r e s s u r e s . M o n i t o r i n g of oxygen p a r t i a l p r e s s u r e s in g a s e s via this technique has been used in s t u d i e s of 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 y g e n - b e a r i n g s y s t e m s such as the V203-VO2 s y s t e m 6 and in k i n e t i c s t u d i e s such as the oxidation of i r o n 7,8 and w u s t i t e , 7 the r e d u c t i o n of m e t a l oxides, 7,9 the d e c a r b u r i z a t i o n of liquid m e t a l s , ~~ and oxygen a b s o r p t i o n by liquid copper and copper a l l o y s J 2 The t i t r a t i o n of oxidizable g a s e s with a i r , 13 the a m p e r o m e t r i c t i t r a t i o n of gas mixtures,~4 and the p u r i f i c a tion of g a s e s x5 can be followed. In addition, m e a s u r e m e n t s of oxygen p r e s s u r e s with a u x i l i a r y oxygen p r o b e s were e s s e n t i a l d u r i n g i n v e s t i g a t i o n s of the p e r m e a b i l i t y ~8-~8 and p o l a r i z a t i o n b e h a v i o r ~9 of oxide e l e c t r o l y t e s . C o n v e r s e l y , c e l l s having g a s e s of known c o m p o s i t i o n s have enabled e l e c t r o n i c t r a n s p o r t n u m b e r s of e l e c t r o l y t e s b a s e d o n Z r O 2 , 20-28 ThO2, 2~ CeO2, 2~ and ZrOz-CeO233 to be d e t e r m i n e d by t o m T. H. ETSELL, formerly Graduate Student, Department of Metallurgy and Materials Science, University of Toronto, Toronto, Ontario, Canada, is now a National Research Council of Canada Postdoctoral Fellow, Max-Planck-Institutfuer Chemie, Mainz, Germany. S.N. FLENGAS is Professor, Department of Metallurgyand Materials Science, University of Toronto. Manuscript submitted March 17, 1971. METALLURGICALTRANSACTIONS
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