| 2025 №02 (04) |
DOI of Article 10.37434/tpwj2025.02.05 |
2025 №02 (06) |
The Paton Welding Journal, 2025, #2, 30-37 pages
Refining metallurgical silicon
G.G. Didikin, V.O. Osokin, Ya.A. Stelmakh
E.O. Paton Electric Welding Institute of the NASU. 11 Kazymyr Malevych Str., 03150, Kyiv, Ukraine. E-mail: didikin@paton-icebt.kiev.uaAbstract
The review presents modern technologies used to refine metallurgical silicon to a purity of 5‒6 N for photovoltaic cells. Refining of silicon is performed using an intermediate metal Al to capture silicon impurities after its fusion with Si. The removal of C, Ca, Fe, Ti, P from the Al-Si melt with Si is shown. After a two-time directional crystallization of the melt, Si of a purity acceptable for use in photovoltaic technologies was produced. Positive results were obtained during plasma remelting with the simultaneous application of gases in the core: Ar‒H2, H2‒H2O, O2, or H2 in an Ar-based plasma. The electromagnetic stirring of the bath provides accelerated mass transfer in the liquid compared to the reaction rate on the surface with control of the surface shape. Removal of metal impurities Na, Ca, Ba, and Al up to 90‒100 % was achieved using 30 % H2 in Ar plasma. Carbon removal was observed using oxygen in the plasma at temperatures above 1530 °C. It was found that H2 is more effective in plasma than O2. A constant voltage in the liquid bath increases the refining efficiency by 10 times. The best results in removing boron from molten silicon were obtained by blowing the melt with humidified argon or water vapor. The resulting silicon product had favorable electronic properties. It is noted that during electron beam remelting, it is possible to purify silicon from elements with high vapor pressure and perform oxidative refining from boron impurities using a mixture of oxygen and inert gas with application of a cold hearth and zone recrystallization. In the process of EBCZM, after increasing the vacuum depth, the amount of oxygen and phosphorus in silicon can be reduced by a factor of 10.
Keywords: metallurgical silicon, purification, vacuum and oxidative refining, plasma remelting, electron beam melting, silicon, solar grades, impurity elements
Received: 10.06.2024
Received in revised form: 31.10.2024
Accepted: 16.01.2025
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