Authors' reply The role of SiO(I) in the production of metallic silicon
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Authors' Reply The Role of SiO(I) in the Production of Metallic Silicon M. NAGAMORI, I. MALINSKY, and A. CLAVEAU A ternary system where two constituents can be gaseous may be represented graphically by choosing the chemical potentials of two independent gases as coordinates (Kelloggian predominance diagram), while temperature is fixed constant. The other types of ternary diagrams, such as a two-dimensional plot of a partial pressure vs l / T , are not Kelloggian nor complete, being sometimes misleading because one degree of freedom remains unspecified or only partially specified. Two condensed phases cannot be equilibrated unless they are adjacent to one another on the Kelloggian diagram. Accordingly, when a new phase of SiO(l) is incorporated in the predominance diagram, a very different set of equilibrium phase relations comes about in the Si-C-O system. The Kelloggian concept can be best represented by a threedimensional diagram, as often done for metal-sulfur-oxygen (M-SO:-O2) systems, with temperature as the third vertical axis. Such a three-dimensional diagram is shown in Figure 1, where only the Si(I)-SiO(l) and SiC(s)-SiO(l) interfaces are shown. The thermodynamic data and symbols for the univariant points are the same as in the authors' earlier paper.' Some additional free energy data pertinent to the Si-C-O system are presented in Table I. 2-6 Using these and some other literature data, the partial pressures of various gases over the univariant point A and the imaginary (metastable)
LOG Pco
-z 0
LOG O C ~ I mO0*c
REFERENCES 1. M. Nagamori, 1. Malinsky, and A. Claveau: Metall. Trans. B, 1986, vol. 17B, pp. 503-14. 2. W.A. Krivsky and R. Schuhmann, Jr.: Trans. TMS-AIME, 1961, vol. 221, pp. 898-904. 3. A. Schei and O. Sandberg: 'in Selected Topics in High Temperature Chemistry, T. F~rland, K. Grjotheim, K. Motzfeldt, and S. Urnes, eds., Universitetsforlaget, Oslo, 1966, pp. 141-50. 4. A. Schei: Tidsskr. Kjemi, Bergves,, Metall., 1969, vol. 27, pp. 152-58. 5. S. Gjerstad: "Chemical metallurgical investigations concerning carbothermic reduction of alumina and silica," Thesis, Norw. Inst. Techn., Trondheim, 1968, 123 pp. (in Norwegian). See also K. Motzfeldt: Travaux du ComitE international pour I 'etude des bauxites, de I'alumine et de l'aluminium, 1981, vol. 11, No. 16, Acad6mie Yougoslave des Science et des Arts, Zagreb, 1981, pp. 145-60. 6. M.B. Miiller, S.E. Olsen, and J. Kr. Tuset: Scand. Journ. Metall., 1972, vol. 1, pp. 145-55. 7. T. Rosenqvist: Principles of Extractive Metallurgy, 2nd ed., McGrawHill Book Co., New York, NY, 1983, pp. 377-80. 8. O. Kubaschewski and C. B. Alcock: Metallurgical Thermochemistry, 5th ed., Pergamon Press, New York, NY, 1979, pp. 221-26. 9. H.v. Wartenberg: Z. Elektrochem., 1949, vol. 53, pp. 343-47. 10. P.V. Gel'd and M.I. Kochnev: Zh. Priklad Khim, 1948, vol. 21, pp. 1249- , quoted from Ref. 8. 11. L. Coudrier, D.W. Hopkins, and I. Wilkomirsky: Fundamentals of MetallurgicalProcesses, 2nd ed., Pergamon Press, Oxford, etc., 1985,. pp. 170-72.
472--VOLUME 18B, JUNE 1987
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