Electrolytic Reduction of SiO2 Granules in Molten CaCl2

Direct electrolytic reduction of SiO2 was investigated in molten CaCl2 at 1123 K as a fundamental study to develop a continuous process for solar-grade Si production. Several different types of SiO2 granules, as well as SiO2 pellets, were successfully reduced to Si on the bottom cathode of a Si plate. Three parameters were varied in the reduction of SiO2 granules: electrode potential, layer thickness of the SiO2 granules, and SiO2 particle size. The reduction rate was evaluated by the magnitude of the reduction current. The main factor determining the reduction rate was the diffusion of O2− ions inside the reduced porous Si layer filled with the electrolyte. Another factor which influenced the reduction rate was the contact resistance between Si granules.