Electrochemical determination of the free energy of formation of SnO 2
- PDF / 146,701 Bytes
- 2 Pages / 614.28 x 794.28 pts Page_size
- 29 Downloads / 228 Views
Communications Electrochemical Determination of the Free Energy of Formation of Sn02
--
t
w h e r e E i s the o p e n - c i r c u i t E m f and F i s the F a r a d a y c o n s t a n t . T h e 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 SnO2, AG~(SnO2), is given by:
~
A~A 0.480 -
1.1_ W _J _J W
I [ I I I I Cu, Cu20 / Zr 02(Co0)/Sn, Sn02
0.500 ~ n ~
0.46( 0.44( 0.420
q
I
[2],
I
823 873 = -4EF
+ 2 AG;(Cu20).
[41
T i n s t i c k s (99.99 pct), c o p p e r p o w d e r (99.99 pct), SnO2 p o w d e r (99.95 pct) and Cu20 p o w d e r (99.95 pct) w e r e u s e d in the e x p e r i m e n t s . C r u c i b l e s of c a l c i a s t a b i l i z e d z i r c o n i a of a p p r o x i m a t e l y 1 in. length and 1/2 in. ID w e r e o b t a i n e d f r o m the Z i r c o n i u m C o r p o r a t i o n of A m e r i c a . T h e c e l l a s s e m b l y i s shown in F i g . 1. T h e s t a b i l i z e d z i r c o n i a c r u c i b l e c o n t a i n i n g tin chips and SnO2 was p l a c e d in an o u t e r c r u c i b l e c o n t a i n i n g t h o r o u g h l y m i x e d c o p p e r and c u p r o u s oxide p o w d e r s (1 : 1 by vol). C h r o m e l w i r e was u s e d a s the e l e c t r i c a l l e a d for both Cu-Cu20 and Sn-SnO2 e l e c t r o d e s . T h e s u r f a c e of the c h r o m e l w i r e c o n t a c t i n g the SnSnO2 e l e c t r o d e was s l i g h t l y o x i d i z e d . Such a l e a d h a s b e e n u s e d s u c c e s s f u l l y in m o l t e n tin p r e v i o u s l y , z A p y r e x r i n g was p l a c e d b e t w e e n the c r u c i b l e and the c r u c i b l e lid. Slight p r e s s u r e could be e x e r t e d on the c r u c i b l e lid by m e a n s of an a l u m i n a p u s h - r o d . T h e c e l l was p l a c e d in the c o n s t a n t t e m p e r a t u r e zone (~:1 K) of a v e r t i c a l K a n t h a l - w o u n d r e s i s t a n c e f u r n a c e . T h e c e l l was h e a t e d to a t e m p e r a t u r e of 1173 K in an a t m o s p h e r e of p u r i f i e d a r g o n g a s . D u r i n g t h i s p e r i o d the p y r e x r i n g s o f t e n e d and a p y r e x s e a l was f o r m e d , s e p a r a t i n g the i n n e r Sn-SnO2 e l e c t r o d e f r o m the o u t e r
I
923
I
I
I
I
973 1023 10713 1123
TEMPERATURE K Fig. 2--Cell emf as a function of temperature.
Cu-Cu20 e l e c t r o d e . T h e u s e of such a p y r e x s e a l h a s b e e n p r e v i o u s l y r e p o r t e d . 2 T h e o p e n - c i r c u i t E m f of the c e l l w a s m e a s u r e d u s i n g a h i g h - i m p e d a n c e (input i m p e d a n c e >10 l~ o h m s ) e l e c t r o n i c v o l t m e t e r . The c e l l E m f was t a k e n to b e s t e a d y if the r a n d o m v a r i a t i o n was within 1 mV o v e r a five hour p e r i o d . T h e c e l l was c o o l e d and the s t e a d y E m f r e a d i n g s w e r e t a k e n at 50 d e g i n t e r v a l s down to a t e m p e r a t u r e of 773 K. A t e a c h t e m p e r a t u r e , the r e v e r s i b i l i t y of the c e l l was c h e c k e d by p a s s i
Data Loading...
