Wettability of Carbon (C), Silicon Carbide (SiC), and Silicon Nitride (Si 3 N 4 ) with Liquid Silicon (Si)
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https://doi.org/10.1007/s11837-020-04369-0 2020 The Minerals, Metals & Materials Society
SILICON PRODUCTION, REFINING, PROPERTIES, AND PHOTOVOLTAICS
Wettability of Carbon (C), Silicon Carbide (SiC), and Silicon Nitride (Si3N4) with Liquid Silicon (Si) HARISH IYER,1 YUCHANG XIAO ,2,5 DAMIAN DURLIK,3 KARIM DANAEI,4 LEILI TAFAGHODI KHAJAVI,2 and MANSOOR BARATI4 1.—Shawcor, Toronto, ON M9W 1M7, Canada. 2.—University of British Columbia, Vancouver, BC V6T 1Z4, Canada. 3.—RBC, Toronto, ON M5J 1J1, Canada. 4.—University of Toronto, Toronto, ON M5S 1A1, Canada. 5.—e-mail: [email protected]
Separation of the solid inclusions formed during the refining process is one of the major challenges associated with metallurgical refining of silicon (Si). Wettability of solid carbon (C), silicon carbide (SiC) and silicon nitride (Si3N4) substrates with liquid silicon was examined using sessile drop technique. This study was performed with the aim of finding the appropriate temperature for separating the above inclusions from liquid Si. Silicon of 6 N + purity was melted over each substrate and contact angle was measured in the temperature range of 1420C to 1525C in a slightly reducing atmosphere for each system. The contact angle for C-Si is 14 at 1420C and reaches the value of 11 at 1520C. In the same temperature range, the contact angle for SiC-Si system decreases from 46 to 37. The effect of temperature on contact angle is more pronounced for Si3N4-Si system with a decline from 108 to 68 in the range of 1435–1525C.
INTRODUCTION Solar energy is considered one of the most abundant and attractive sources of energy because of its clean and non-polluting nature. Photovoltaic (PV) technology is the most common method of sequestering solar energy. Si, which is the dominant PV material, is typically produced through the Siemens process. The purification process is based on the conversion of metallurgical grade Si (98–99.5%) to a volatile Si compound (e.g., silicon tetrachloride or trichlorosilane), which is purified by distillation and subsequently decomposed to high-purity elemental Si.1 Metallurgical refining is an alternative approach for producing solar-grade Si (6–7 N). Metallurgical refining techniques such as solvent and slag refining consume less energy compared with the Siemens process. However, one common challenge with the metallurgical routes is the separation of the residual solid inclusions, which are formed during the refining processes.
(Received June 5, 2020; accepted August 28, 2020)
Investigating the wettability of these inclusions by liquid Si is critical to understand the difficulties associated with their removal. The ease of physical separation of solid inclusions from Si is often described by the wetting behavior, i.e., the interaction between a bulk material (liquid Si) and the impurities (solid inclusions). Young’s equation, shown below, can be used to explain the interfacial/surface tensions in the solid–liquid–vapor system and the apparent form of contact between the two phases, known as co
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