Separation Mechanism of Primary Silicon from Hypereutectic Al-Si Melts Under Alternating Electromagnetic Fields
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CHEMICALLY pure SOG-Si or Si, often utilized in photovoltaic applications, are rather costly materials. The solidification of silicon is a well-known process for the manufacture of SOG-Si.[1] Many previous researchers have developed successful processing methods, including directional solidification,[2] vacuum melting,[3] and oxidation treatment.[4] However, these methods require very high temperature [>1700 K (1427 C)]. Because Al-Si systems have a lower melting point than silicon, purification of silicon from hypereutectic Al-Si melts can be realized at the distinct advantage of lower energy consumption.[5] Due to the lower segregation ratio of impurities between solid silicon and Al-Si melts than that between solid silicon and liquid silicon, the purification of silicon from a hypereutectic Al-Si melt is HAIYANG XUE, Student, GUOQIANG LV and JIE YU, Assistant Professors, and WENHUI MA, Professor, are with the State Key Laboratory of Complex Nonferrous Metal Resources Cleaning Utilization in Yunnan Province/The National Engineering Laboratory for Vacuum Metallurgy, Kunming University of Science, and Technology, Kunming 650093, P.R. China, and with the Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, and also with the Key Laboratory of NonFerrous Metals Vacuum Metallurgy of Yunnan Province/ Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities, Kunming 650093, P.R. China. Contact e-mail: [email protected] DAOTONG CHEN, Student, is with the Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, and also with the Key Laboratory of Non-Ferrous Metals Vacuum Metallurgy of Yunnan Province/Engineering Research Center for Silicon Metallurgy and Silicon Materials of Yunnan Provincial Universities. Manuscript submitted November 26, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS A
more effective.[6,7]Therefore, silicon purification from hypereutectic Al-Si melts has become a hot research topic in recent years.[5–11] Hypereutectic Al-Si alloys are widely used in aerospace and automotive applications favored for their high wear resistance, low density, corrosion resistance, and high thermal stability. The most common methods of manufacturing hypereutectic Al-Si alloys are the mixing method, molten salt electrolysis, and the electrothermal method—the cost of which, unfortunately, can be quite high. The electrothermal method does not effectively produce hypereutectic Al-Si alloys with low silicon such as A390 (16 to 18 pct Si), A392 (18 to 20 pct Si), and A393 (21 to 23 pct Si), though these are very useful in the field. It does seem possible to manufacture hypereutectic Al-Si alloys with low silicon in a more cost effective manner if the silicon can just be separated from hypereutectic Al-Si alloys with high silicon. Both purification of silicon and manufacture of hypereutectic Al-Si alloys with low silicon require separating the silicon phase from the hypereutectic AlSi alloy. Effect
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