Potentiostatic polarization measurements on solid platinum-molten PbO-GeO 2 , PbO-SiO 2 , and Na 2 O-SiO 2 interfaces
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ELECTRICAL conductivity measurements and electrolysis of molten silicates have been carried out since the 1940's. 1'2 These studies have revealed that many molten silicates are ionic conductors; namely, they can be used as electrolytes for galvanic cells.3 Therefore, when an electrical charge is carried across the solid platinum-molten silicates interfaces, a charge transfer process will occur. The mechanism of this process has not yet been examined. However, it is important for the physicochemical studies of molten oxide solutions, such as Faradaic impedance included in the conductivity measurements of slags4 and electrochemical investigations of slag,-metal reactions.S The purpose of the present work is to investigate the mechanism of the charge transfer process by potentiostatic polarization measurements. The molten oxide solutions investigated are PbO-GeO2, PbO-SiO2, and Na20-SiOz. The applied potential range is from -20mV to +30mV from their equilibrium potential.
v a l u e , the p o t en t i al d i f f e r e n c e d e t e c t o r (B) o p e r a t e d and the c u r r e n t b et w een the w o r k i n g e l e c t r o d e and the co u n t er e l e c t r o d e w as c o n t r o l l e d , so a s to m a i n tain the a s s i g n e d c o n s t a n t p o t e n t i a l . The i n t e r f a c e a r e a of the w o r k i n g e l e c t r o d e w as about 0.4 c m 2. P r e p a r a t i o n of oxide so l u t i o n s w as as f o l l o w s . Two kinds of d r i e d oxide p o w d e r s w e r e w e i g h e d and m i x e d to the d e s i r e d c o m p o s i t i o n . The m i x t u r e w as m e l t e d in a p l a t i n u m c r u c i b l e and quenched on a w a t e r - c o o l e d
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EXPERIMENT A s c h e m a t i c d i a g r a m of the c e l l a s s e m b l y and c i r cuit u s e d is shown in F i g . 1. The c r u c i b l e for the m o l t e n o x i d e s and the t h r e e e l e c t r o d e s w e r e m a d e of p l a t i n u m . One of the e l e c t r o d e s w a s not p o l a r i z e d , b e c a u s e no c u r r e n t flowed. T h i s one w a s u s e d a s a r e f e r e n c e e l e c t r o d e and as a t h e r m o c o u p l e c o n n e c t e d with 13 pct R h - P t w i r e . The p a r t e n c l o s e d by dotted l i n e s in the f i g u r e shows a s c h e m a t i c d i a g r a m of the p r i n c i p l e of the p o t e n t i o s t a t . The e l e c t r o c h e m i c a l poten t i al of the w o r k i n g e l e c t r o d e to the r e f e r e n c e e l e c t r o d e was m e a s u r e d by the p o t e n t i o m e t e r (POT). If the m e a s u r e d p o t e n ti a l d e v i a t e d f r o m the a s s i g n e d
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M. KAWAKAMIand K. S. GOTO are Research Associate and Associate Professor, respectively, Department of Metallurgical Engineering, Tokyo Kogyo Daigaku, Tokyo, Japan. Manuscript submitted May 15, 1972.
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