Direct electrolytic reduction of solid SiO2 in molten CaCl2 for the production of solar grade silicon

The direct electrolytic reduction of solid SiO2 has been investigated in molten CaCl2 at 1123 K aiming at the production of solar grade silicon (SOG-Si). A new type of SiO2 contacting electrode was prepared to prevent the metal contamination from a conducting wire; the top end of an SiO2 glass plate was put between two single crystal silicon plates and they were wound by a molybdenum wire. A silicon ingot was successfully produced from the electrochemically reduced samples by separating the silicon from the unreduced SiO2 by means of a melting process under vacuum at 1773 K. The purity of the silicon ingot was 99.80 at.% at this stage, due to the metal contamination from the stainless vessel. However, the concentrations of boron and phosphorus were very low in the ingot, which verifies the applicability of this electrochemical process for the SOG-Si production. (C) 2007 Elsevier Ltd. All rights reserved.