Electrolytic reduction of SiO₂ granules in molten CaCl ₂

Direct electrolytic reduction of SiO₂ was investigated in molten CaCl₂ at 1123K as a fundamental study to develop a continuous process for solar-grade Si production. Several different types of SiO ₂ 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 O_2- 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.