Thermodynamics of calcium and oxygen in molten Ti 3 Al
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5 2MgOzAl2O3 (s) 1 Ca DG714 5 298,870 2 149.82T (J/mol)
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7. 8. 9.
CaO (s) 1 2Al2O3 (s) 5 CaOz2Al2O3 (s)
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DG716 5 15,650 1 25.82T (J/mol)
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These equilibrium oxides, however, are harmful inclusions in produced steel, so the stability area of liquid nonmetallic inclusion formed by deoxidation has to be shown from the viewpoint of shape control of nonmetallic inclusions. The activity of each constituent in the CaO-Al2O3-MgO system, such as aAl2O3, aMgO, or aCaO, was quoted in the calculation from our previous study,[11,12] where the regular solution model was applied to evaluate their activities. The calculated stability phase diagram is shown in Figure 5. The evaluated liquid phase area agreed well with the liquidus lines observed in our previous work.[11,12] The main findings of this study on the thermodynamics of spinel nonmetallic inclusion formation in liquid iron can be summarized as follows.
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(1) The equilibrium constants and interaction parameters on calcium, magnesium, and aluminum deoxidation in liquid iron at steelmaking temperature must be expressed by the first-and second-order interaction parameters, including cross-product terms. (2) Stability phase diagrams of MgO-MgOzAl2O3-Al2O3 and MgO-MgOzAl2O3-CaOz2Al2O3 were drawn at steelmaking temperatures as a function of dissolved magnesium, aluminum, calcium, and oxygen contents in liquid iron. (3) The liquid oxide phase area in the stability phase diagram of the MgO-Al2O3-CaO ternary system was determined at steelmaking temperatures.
This study was sponsored by a Grant-in-Aid for Iron and Steel Research from The Iron and Steel Institute of Japan in 1994 and 1995. The authors are grateful to Yoshizawa Lime Industry for providing one of the authors (Y1) with financial support during his stay at Tohoku University. They wish to thank former undergraduate students, Messrs. H. Suzuki (now with Chuo Spring Co., Ltd.) and T. Suzuki (now with MEMC), from Tohoku University for their effective assistance in making the experiments.
REFERENCES 1. T. Ototani, Y. Kataura, and T. Degawa: Tetsu-to-Hagane´, 1975, vol. 61, pp. 2167-81. 2. C.H. Lupis: Chemical Thermodynamics of Materials, North-Holland, Amsterdam, 1983, pp. 254 and 256. 3. Y. Itoh, M. Hino, and S. Ban-ya: CAMP-ISIJ, 1995, vol. 8, pp. 7578; Y. Itoh: Ph.D. Theses, Tohoku University, Sendai, 1996. 4. M. Hino, H. Itoh, and S. Ban-ya: Japan-US Joint Seminar, Clean Steel for the 21st Century: Fundamental Issues, Futtsu, Chiba, Japan, Apr. 25–27, 1996, The Japan Society for The Promotion of Science and The National Science Foundation, Tokyo, 1996, pp. 125-30. 5. Steelmaking Data Sourcebook, The Japan Society for the Promotion 956—VOLUME 28B, OCTOBER 1997
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of Science, The 19th Committee on Steelmaking, Gordon and Breach Science Publishers, New York, NY, 1988, p. 45. L.E. Rohde, A. Choudhury, and M. Wahlster: Arch. Eisenhuttenwes., 1971, vol. 42, pp. 165-67. N.S. Jacobson and G.M. Mehrotra: Metall. Trans. B, 1993, vol. 24B, pp. 484-86. N.A. Gokcen and J. Chipman: J. Met., 195
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