thermodynamic properties of liquid Ag-Si alloys
- PDF / 513,652 Bytes
- 5 Pages / 612 x 783.28 pts Page_size
- 7 Downloads / 232 Views
I Si4ยง I
Mo, Si (s) (sat. (-) in liq. Ag) Li20-SiO2 Si (in liq. (+)Ag), Mo SiO2(sat.) The overall process in the cell with the passage of positive current from the left electrode to the right in the cell is the transfer of silicon from a chemical potential of pure solid silicon on the left, ~Si, o at its HIROSHI SAKAO, Member of AIME; Visiting Scientist, Mass. Instit. Technology, Cambridge, Mass. (1969) is Professor, Faculty of Engineering, Nagoya University, Nagoya-shi, Japan. JOHN F. ELLIOTT, Fellow of TMS and of ASM, is Professor of Metallurgy, Mass. Inst. Technology, Cambridge, Mass. 02139. Manuscript submitted February 7, 1974. METALLURGICAL TRANSACTIONS
c h e m i c a l p o t e n t i a l in the A g - S i solution, ~ s i , on the right. S i ( s ) ~ S i ( a l l o y ) ; AG = ~ S i -
o
~si =-4~e
[1]
The c h a r g e t r a n s f e r r e a c t i o n s p e r a t o m of s i l i c o n at e a c h e l e c t r o d e with a s i l i c a t e e l e c t r o l y t e invoIved 4 e l e c t r o n s 9 (Z = 4). 9 is F a r a d a y ' s c o n s t a n t , 96,487 c o u l o m b s p e r e q u i v a l e n t . The a c t i v i t y , a~i , a c t i v i t y c o e f f i c i e n t , ~si, and e x c e s s r e l a t i v e p a r t i a l m o l a r e n t r o p y of s i l i c o n in the a l l o y s , S Xs is, a l l r e l a t i v e to p u r e s o l i d s i l i c o n a s i n d i c a t e d b y the s u p e r s c r i p t s , a r e o b t a i n e d d i r e c t l y f r o m the r e v e r s i b l e p o t e n t i a l of the c e l l , ~, a s f o l l o w s : In aSsi : - Z ~ s In yssi = - Z ~ E / R T -
[2] In Xsi
S E s = Z ~ B e ~ a T - R In x s i
Si
[3] [4]
Xsi is the a t o m f r a c t i o n of s i l i c o n in the liquid a l l o y . The d e s i g n of the c e l l is shown in F i g . 1. L i t h i u m s i l i c a t e was s e l e c t e d a s the e l e c t r o l y t e p r i m a r i l y b e c a u s e 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 Li20 (per m o l e of O2) is a p p r o x i m a t e l y 120 k J m o r e n e g a tive than that of s i l i c a . Thus, the r e d u c t i o n of l i t h i u m into the e l e c t r o d e s by the r e a c t i o n b e t w e e n s i l i c o n and Li20 is e s s e n t i a l l y avoided. It is to be noted that p r e l i m i n a r y m e a s u r e m e n t s with a s o d i u m - s i l i c a t e e l e c t r o l y t e m e t with f a i l u r e b e c a u s e of the exchange r e a c tion involving s i l i c o n and s o d i u m . A s e c o n d r e a s o n f o r s e l e c t i n g l i t h i u m s i l i c a t e m e l t s f o r the e l e c t r o l y t e is that t h e r e is a e u t e c t l c at 19 wt pct Li20 and 1030~ 1~ A c c o r d i n g l y , the e l e c t r o l y t e can be a m i x t u r e of the e u t e c t i c liquid and s o l i d p a r t i c l e s of p u r e s i l i c a o v e r the t e m p e r a t u r e r a n g e of i n t e r e s t , i . e . , 1100 to 1325~ An e l e c t r o l y t e s a t u r a t e d with s i l i c a p e r m i t t e d use of s i l i c a a s the r e f r a c t o r y m a t e r i a l for the c e l l . The a
Data Loading...
