A thermodynamic study of the carbothermic reduction of alumina in plasma
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Yo-~ + 4ys,o,-" + 3ysio3 -2 + 2ys,o~0 4ysio4 -4 + 2ys,o3-~
fo-,
=
yo-2 + 4ys,o4-4 + 3ysio3-2 + 2yslo:0
fo 0 =
Ysio3-2 -~- 2ys~o20
yo-2 + 4ys,o,-4 + 3ysio3-2 + 2ysio20
We can also evaluate the average number of broken or unbroken bridges per Si atom: no-i
4ys,o,-4 + 2yslos-2 Ys~o4-4 + Ysio3-2 + Ysio20
no 0 =
Ys,o3-: + 2ys,o2 ~ YS~O4 4 + Ysio3-2 + Ys~o20
Then we can apply the statistical method of Lin and Pelton [7] for an evaluation of the distribution of polymeric anions. Various models for silicate melts are reviewed, and the difficulty of constructing a model covering the whole range of compositions is emphasized. A new model for silicate melts, which has been constructed by combining the Flood and Knapp TM model for the metal oxide-rich side and a new model for the SiO2-rich side, appears to have attractive properties. The value of the model can only be tested by application to real cases. It has been applied to the MgO-SiO2 system, tl~ and in an accompanying paper, it will be applied to the CaO-SiO2 system.
This work has been financially supported by the Swedish Board for Technical Development.
REFERENCES 1. M. Hillert, B. Jansson, B. Sundman, and J. /~gren: Metall. Trans. A, 1985, vol. 16A, pp. 261-66. 2. H. Flood and W.J. Knapp: J. Am. Chem. Soc., 1963, vol. 46, pp. 61-65. 3. C.R. Masson, I.B. Smith, and S.G. Whiteway: Can. J. Chem., 1970, vol. 48, pp. 1456-64. 4. C.R. Masson: Proc. R. Soc., 1965, vol. A287, pp. 201-21. 406--VOLUME 21B, APRIL 1990
5. C.J.B. Fincham and F.D. Richardson: Proc. R. Soc., 1954, vol. 223, p. 40. 6. T. Feirland: Fused Salts, B.R. Sundheim, ed., McGraw-Hill, New York, NY, 1964, ch. 3. 7. P.L. Lin and A.D. Pelton: Metall. Trans. B, 1979, vol. 10B, pp. 667-75. 8. A.D. Pelton and M. Blander: presented at CALPHAD XI, Argonne National Laboratory, Argonne, IL, 1982. 9. M. Temkin: Acta Physicochim., URSS, 1945, vol. 20, pp. 411-20. 10. M. Hillert and X. Wang: CALPHAD, 1989, vol. 13, pp. 253-66.
A Thermodynamic Study of the Carbothermic Reduction of Alumina in Plasma C.M. WAI and S.G. H U T C H I S O N The production of certain metals by conventional processes often requires high electric energy consumption. For this reason, increasing attention has recently been given to applications of plasma smelting for mineral processing, tl-6] Rains and Kadlec, for example, studied the reduction of alumina to aluminum in radio frequencygenerated plasmas. Is1 An appreciable conversion of the oxide to the metal was reported. However, extensive thermodynamic studies to determine species distribution were not attempted. Alcock performed thermodynamic calculations to evaluate the potential for the carbothermic reduction of a number of metal oxides in the plasma temperature range of 1000 to 3000 K. TM Based on free energies of vaporization, Alcock noted that the carbothermic reduction reaction of alumina should be possible at temperatures above 2000 K. The reduction reaction is very complex, with a number of gaseous species as well as condensed phases including the carbide, Al4C3, and the oxyc
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