Reaction Behavior of Stratified SiO2 Granules during Electrochemical Reduction in Molten CaCl2

The electrochemical reduction behavior of stratified SiO2 granules in molten CaCl2 at 1123 K (850 A degrees C) was investigated to develop a new process for producing solar-grade silicon. The cross sections of the electrolyzed electrode prepared from a graphite crucible filled with SiO2 granules were observed and analyzed. The visual and SEM observations indicate that the overall reduction proceeds via two different routes. In one route, the reduction proceeds along the granule surfaces from the SiO2 near the conductor to the distant SiO2. In the other route, the reduction proceeds from the granule surface to the core of each granule. The reduction along the granule surfaces is faster than that from the surface to the core. Fine SiO2 granules are expected to be favorable for a high reduction rate. (C) The Minerals, Metals & Materials Society and ASM International 2014