Effect of electrolysis potential on reduction of solid silicon dioxide in molten CaCl2

Electrochemical reduction of solid SiO2 by using a contacting electrode method was investigated in molten CaCl2 at 1123 K. The samples were prepared by potentiostatic electrolysis at 0.35-1.30 V (vs. Ca2+/Ca) for 1 h. From the results of XRD, SEM and EPMA, it was confirmed that SiO2 was electrochemically reduced to Si at 1.25 V or more negative potential, which agreed with the thermodynamic calculation. The current-time curves during electrolysis and the cross-sectional SEM measurements of the samples clearly showed that reduction rate is higher at more negative potential. In addition, Si-Ca alloy formation was confirmed at 0.35 V.