Abstract
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.
Highlights
A new Ti production process replacing the Kroll process is desired
The Ti deposition strongly depended upon the molar ratio of CaO to TiO2 (RCaO/TiO2, hereinafter), and RCaO/TiO2 = 1.5 seemed suitable for Ti metal deposition.[9, 10]
Based on these results in molten fluoride, Ti metal deposition in molten CaCl2 containing some types of calcium titanate was attempted above 1300 K, and it was shown that Ti metal was deposited under a particular condition; RCaO/TiO2 was dominant even in molten CaCl2, and the electrolysis potential affected the deposition.[11,12,13]
Summary
A new Ti production process replacing the Kroll process is desired. Many researchers have been studying the innovative smelting process,[1,2,3,4,5,6,7] but those processes are still under development. Ti metal deposition in molten CaCl2 containing some types of calcium titanate was attempted, and the influence of RCaO/TiO2 on Ti metal deposition was discussed in comparison to that in molten fluoride. It is discussed the differences from Ca and Al metal deposition in molten CaCl2 above 1373 K which the authors have been studying.[14]
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