Electrolytic Reduction of Solid SiO₂ in Molten CaCl₂ for the Production of Solar-grade Silicon

Abstract

The direct electrolytic reduction of solid SiO 2 has been investigated in molten CaCl 2 at 1123 K aiming at the production of solar grade Si. The target impurity levels for Si in the present study were calculated from the acceptable impurity levels for SOG-Si and the segregation coefficients for the impurity elements. New types of SiO 2 contacting electrodes, in which SiO 2 directly contacts with only Si, were devised to reduce metal contaminations in the produced Si. By using the new SiO 2 contacting electrodes and a quartz vessel, most of the metal impurities were significantly reduced to be below the target levels. When NH 4 OH/H 2 O 2 /H 2 O, HCl/H 2 O 2 /H 2 O and HF/H 2 O 2 /H 2 O were used as a cleaning solution, remaining CaCl 2 and some metal impurities in the produced Si were removed effectively. A basket type electrode was also tested for the reduction of granular SiO 2 .