The standard free energy of formation of Cr 3 C 2 by the electromotive force method
- PDF / 312,395 Bytes
- 3 Pages / 569 x 813.28 pts Page_size
- 91 Downloads / 189 Views
8
~-Cr3C2 + 02 : ~Cr~O3-~ ~-C (g)
[1]
The following c e l l was used Cr3C2, CrzO3, C I E l e c t r o l y t e I C r , Cr:O3 w h e r e the r e f e r e n c e e l e c t r o d e r e a c t i o n ls r e p r e s e n t e d by 4
2
5- C r + Oz = 7 Cr~O3
[2]
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 Cr203 is c a n c e l l e d f r o m both e l e c t r o d e s b e c a u s e CrzO3 has only e x t r e m e l y s m a l l d e v i a t i o n s from s t o l c h m m e t r y . C o n s e q u e n t l y the o v e r a l l r e a c t i o n of the c e l l is exp r e s s e d by 9
.
]
[3]
•3 Cr + ~8 C ( g ) : b4 Cr3C~ and 4
o
A G : ~" AGCr3C 2
[4]
w h e r e AC is the f r e e e n e r g y change of the o v e r a l l r e action and A C ~ r ~ is the s t a n d a r d f r e e e n e r g y of f o r mation of Cr~C~:1"~2 On the o t h e r hand, ~,C is r e l a t e d to the e l e c t r o m o tive f o r c e by the N e r n s t equation /', G = - ~ t F E
[ 5]
where E is the electromotive f o r c e , F is the Faraday
Fig. 2--Variation of density as a function of composition. A: Interstitial sulfur, B: substitutional sulfur, C: copper vacancy.
The a u t h o r s a r e g r a t e f u l to D r . A. H. W e b s t e r of the Mines B r a n c h staff for helpful d i s c u s s i o n . 1. P. Rahlfs: 2". Physik. Chem., B., 1936, vol. 31, p. 157. 2. S. Djurle: Aeta Chem. Stand., t958, vol. ! 2, p. ~.415. 3. G. Donnay, J. D. Doanay, and G. Ku[lerud: Am. Mineralogist, 1958, vol, 43, p. 228. 4. N. Morimoto and G. Ku}lerud: Am. Mineralogist, 1963, vol. 48, p. 110. 5. M. Laffitte: Bull. Sea Chbn. France, 1959, p. 1211.
constant and n is the n u m b e r of f a r a d a y s which pass if the r e a c t i o n p r o c e e d s to c o m p l e t i o n , then n is 4. C o m bining E q s . [4] and [hj, 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 Cr~C~ is d e r i v e d f r o m the e l e c t r o m o t i v e f o r c e of the c e l l without any t h e r m o d y n a m i c i n f o r m a lions of o t h e r s u b s t a n c e s .
[6 ]
A C~r.~C2 = - 9 F E
The c e l l c o n s t r u c t i o n is shown in Fig. 1. Both e l e c t r o d e s w e r e d e s i g n e d to be s m a l l and isolated f r o m the e x t e r i o r for the e l i m i n a t i o n of oxygen c o n c e n t r a t i o n g r a d i e n t s . One e l e c t r o d e was a m i x t u r e of powders of CrzC2, Cr.~Os and g r a p h i t e . The r e f e r e n c e e l e c t r o d e was Cr203. The t h o r i a - b a s e d e l e c t r o l y t e s w e r e p r e p a r e d f r o m - 3 2 5 m e s h p o w d e r s of high p u r i t y (99.9+ pet) ThO~ and "~O~.s. M i x t u r e s of 85 m o t e pet ThO~ and 15 mole pet u w e r e p r e s s e d at 2 ton p e r sq cm into pellets of 15 mm diana and 6 m m t h i c k . The p r e s s e d pellets
The Standard Free Energy of Formation of CqC2 by the Electromotive Force Method H. MABUCHI, N. SANd, AND Y. MATSUSHITA T H E standard f r e e energ-y of f o r m a t i o n of Cr3C2 was d e t e r m i n e d by m e a s u r i n g the oxygen e q u i l i b r i u m p r e s s u r e o
Data Loading...
