Metallic Si is produced by carbon reduction of SiO₂ in an arc furnace above 2000K, and the energy consumption and CO₂ exhaustion in the process are very large. The authors reported that TiO₂ could dissolve in molten CaCl₂ containing CaO above 1300K, and that Ti metal was electrodeposited in the bath. This result implies the possibility of electrolytic production of liquid metallic Si in molten CaCl₂-CaO-SiO₂ above its melting point, which can lead the innovative production process of metallic Si with lower energy consumption and lower CO₂ exhaustion. To realize this process, the electrochemical behavior of Si in molten CaCl₂-CaO-SiO₂ at a very high temperature has to be studied in detail. In this study, the cathodic reaction has been investigated in molten CaCl₂-CaSiO₃ above 1300K, and the electrodesipotion of metallic Si has been attempted.

Based on our previous studies on Ti electrolysis, calcium silicate was used instead of CaO and SiO₂. Calcium chloride containing 0~10 mol% CaSiO₃ in a Mo crucible was fused in an air-tight furnace, and electrolysis was carried out at 1373 ~ 1573 K under a pure Ar flow. The working electrode was mainly a Mo wire with an Al₂O₃ sheath, and a SiC rod was also used. Another Mo wire electrode was used as quasi-reference electrode, and its potential was calibrated with Mo dissolution potential in the bath. Cyclic voltammetry was performed to investigate the electrode reactions in the bath, and then potentio-static electrolysis was carried out to obtain electrodeposit. The electrode surfaces after electrolysis as well as the electrodeposit were analyzed by XRD and SEM-EDX.

The cathodic current obviously enlarged with the CaSiO₃ addition, and the CaSiO₃ solubility seemed to increase with the bath temperature. A sharp cathodic current peak appeared around -1.1 V (vs. Mo dissolution potential) at the Mo electrode, while no cathodic current peak was observed at the SiC electrode. Electrodeposit as shown in Fig.1 was obtained at the Mo electrode, and metallic Si was detected in it. Although a MoSi₂ layer was also formed on the surface by electrolysis as shown in Fig. 2, the amount of Si in the layer was limited considering the quantity of electricity during the electrolysis. Since CaSi₂ was sometimes found in the deposit, the suitable electrolytic potential needs to be revealed.

It was shown that metallic Si was obtained by electrolysis in molten CaCl₂-CaSiO₃ under the proper condition. However, the amount of metallic Si on the electrode could not be determined yet because of the powdery morphology of deposit. It should be desirable to obtain liquid metallic Si by electrolysis above its melting point.