Direct electrolytic reduction of solid SiO 2 in molten CaCl 2 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 silicon (SOG-Si). A new type of SiO 2 contacting electrode was prepared to prevent the metal contamination from a conducting wire; the top end of an SiO 2 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 SiO 2 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.