Aiming at direct electrodeposition of liquid metallic Si in molten CaCl2, electrodeposition of metallic Si has been attempted at 1373 ~ 1573K. In molten CaCl2 containing CaSiO3 as Si source, the electrochemical behavior was investigated by cyclic voltammetry. Cathodic current increased with the increase in added amount of CaSiO3, which indicates that the electrochemical reduction of a Si ion occurred in the bath. The results by cyclic voltammetry suggest that the solubility of CaSiO3 enlarged with the temperature increase, and was about 7 mol% at 1573 K. Metallic Si was obtained by potentio-static electrolysis. However, the total amount of metallic Si was still insufficient, and undesirable reactions, such as CaSi2 formation and MoSi2 formation, could not be controlled. To perform better electrolysis, the influence of the type of calcium silicate on Si deposition should be investigated. Suitable cathode material for metallic Si deposition is also a subject to consider.
The dependence of the cathodic behavior of a Ti ion on the molar ratio of CaO to TiO2 (RCaO/TiO2) was investigated in molten CaCl2 above 1373 K, and the influence of RCaO/TiO2 on Ti metal deposition was discussed. The reduction mechanism changed at RCaO/TiO2 = 1.5; a three-step reduction of Ti was suggested in the melt of RCaO/TiO2 < 1.5, while a two-step reduction seemed to occur above RCaO/TiO2 = 1.5. Titanium metal deposition was also affected by RCaO/TiO2 as well as by the cathode potential, and the suitable RCaO/TiO2 was likely 1.5. Since this value was the same as the suitable value in the molten fluoride system, Ti metal was thought to be obtained only from Ti2O76-. Silicon and Al metal were obtained electrochemically in molten CaCl2 containing calcium silicate and aluminate more easily than Ti metal. The difficulty of the Ti metal deposition is likely to be caused by the so-called shuttle reaction; the shuttle reaction can occur in the Ti metal electrolysis because some ionic states of Ti are stable in the bath. To realize better Ti metal deposition, the control of the shuttle reaction should be important.
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