Research on the Electrochemical Behavior of Si(IV) on the Tungsten Electrode in CaCl2–CaF2–CaO Molten Melt

Abstract

At 1023 K, the electrochemical behavior of Si(IV) on the tungsten electrode in CaCl2–CaF2–CaO–SiO2 molten salt was studied by cyclic voltammetry, square-wave voltammetry and open-circuit chronopotentiometry. The reduction potential of Si(IV) started at –0.68 V, and the intermediate product CaC2 was observed at –1.78 V. The reduction of Si(IV) on the tungsten electrode was a one-step four-electron transition, which was a diffusion-controlled mass transfer process. The diffusion coefficient for the reduction process of Si(IV) ions was estimated to be 3.22 × 10–5 cm2 s–1 at 1023 K. With the temperature interval from 993 to 1183 K, the diffusion activation energy was calculated to be 4.425 kJ mol–1. Moreover, the deposition of Si(IV) occurs when the applied potential is less than –0.6 V (vs. Pt wire). The present electrochemical study on Si(IV) in the molten salt will be a theoretical reference for future silicon electrorefining.