The surface tension of liquid silver-copper alloys
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( g a s ) = C a S ( s l a g ) + 1 / 2 0 2 ( g a s ) w h e r e a s E q . [1] i s w r i t t e n a s A101.5 ( s l a g ) + 3 / 2 C ( g r a p h i t e ) + 1 / 2 N2 ( g a s ) = A1N ( s l a g ) + 3 / 2 C O ( g a s ) . B y a p p l i c a t i o n of t h e l a w of m a s s a c t i o n i t i s s e e n t h a t K c y a n i d e , K ~ a r b i d e a n d s u l f i d e c a p a c i t y a r e p r o p o r t i o n a l t o a c a o / ~ " Ca0 sCN, aCaO/yCaC 2 , a C a O / Y C a S ( a = a c t i v i t i e s , y = a c t i v i t y c o e f f i c i e n t ) , r e s p e c t i v e l y . K n i t r i d e is p r o p o r t i o n a l to aAIOt.5/TAIN. I t i s e v i d e n t that the a c t i v i t y / a c t i v i t y coefficient r a t i o s involving t h e Ca containing c o m p o n e n t s i n c r e a s e w h e n calcium fluoride is a d d e d to C a O A12Os m e l t . * ) *It should be mentioned that the dataon carbide solubility reported in this work and in previous literature 3'4are completely at variance with data ofD. M. Edmunds and J. Taylor 'l on the reaction
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CaO (solid oxide) + 2C (graphite) = CaC2(solid carbide) + CO (gas)
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[8]
According t o these authors the carbon monoxide pressure is 3.26 atm for this reaction at 1600°C, and the aca0 value for the 32 wt pct CaO, 32 wt pct A1203, 36 wt pct CaF2 slag is approximately 0.4. If these datawere correct the CO pressure for the equilibrium between the four phases melt, graphite, gas, solid carbide would be 1.3 atm at 1600°C, that is solid carbide should have precipitated under all the atmospheres used. There was no indication that this happened. The equilibrium of reaction [8] has been measured previously I by ourselves yielding Pco = 0.029 atm at 1600°C. This datum is very close t o that computed from the available free energy data of CaO12 CaC2~2 and CO.13
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F i g . 4--Plot of data in accordance with E q . [7].
T h e following n u m e r i c a l v a l u e s were obtained for K c y a n i d e , K n i t r i d e , K c a r b i d e (1600°C, s l a g c o m p o s i tion 32 wt p c t C a O , 32 wt pct A1203, 36 wt p c t C a F 2 )
I. K. Schwerdtfeger andH. G. Schubert: Arch. Eisenhuetten., 1974,vol. 45, pp. 649-55,905. 2. K. Schwerdtfeger and H. G. Schubert: Met. Trans. B., 1977,vol. 4B, pp. 535- 40. 3. H. G. Schubert andK. Schwerdtfeger: Arch. Eisenhuetten., 1974, vol. 45, pp. 437-39. 4 . J. H. Swisher: Trans. TMS-AIME, 1968, vol. 242, pp. 2033-37. 5. R. Juza and H.-U. Schuster: Anorg. Chem., 1961, vol. 311, p p . 62-76. 6 . A. Mitchell: Trans. TMS-AIME, 1968, vol. 242, pp. 2507-11. 7. W. A. Barber andC. L. Sloan: J. Phys. Chem., 1961, vol. 65, p
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