The Role of Granule Size on the Kinetics of Electrochemical Reduction of SiO₂ Granules in Molten CaCl₂

As a fundamental study to develop a new process for producing solar-grade silicon, the effect of granule size on the kinetics of the electrochemical reduction of SiO₂ granules in molten CaCl₂ was investigated. SiO₂ granules with different size ranges were electrolyzed in molten CaCl₂ at 1123 K (850 °C). The reduction kinetics was evaluated on the basis of the growth rate of the reduced Si layer and the behavior of the current during electrolysis. The results indicated that finer SiO₂ granules are more favorable for a high reduction rate because the contact resistance between the bottom Si plate and the reduced Si particles is small and the diffusion of O²⁻ ions in CaCl₂ inside the porous Si shell is easy. Electrolysis using SiO₂ granules less than 0.1 mm in size maintained a current density of no less than 0.4 A cm⁻² within 20 minutes, indicating that the electrochemical reduction of fine SiO₂ granules in molten CaCl₂ has the potential of becoming a high-yield production process for solar-grade silicon.