Dissolution Behavior of SiO₂ and Electrochemical Reduction of Dissolved SiO₂ in Molten Chlorides

Abstract

To develop a new production process for SOG-Si with high productivity and low energy consumption, the structure of silicate ions in molten eutectic NaCl–CaCl₂ containing dissolved SiO₂ was investigated by Raman spectroscopy. The existence of SiO₃²⁻ was indicated in melts containing 1.0 mol% of CaSiO₃ (O²⁻/SiO₂ = 1.0). When 1.0 mol% of CaO was further added to the melt (O²⁻/SiO₂ = 2.0), the existence of SiO₄⁴⁻ was indicated. Cyclic voltammetry and potentiostatic electrolysis were conducted in molten NaCl–CaCl₂ with different silicate ions. From cyclic voltammograms, XRD analysis, and SEM observation, silicate ions with different structure indicated different electrochemical reduction behavior; and the SiO₃²⁻ ion is likely to be more suitable than SiO₄⁴ ion for the electrodeposition of Si.