Reduction of TiO<SUB>2</SUB> in Molten CaCl<SUB>2</SUB> by Ca Deposited during CaO Electrolysis

Abstract

Fundamental experiments are conducted to confirm the calcium reactivity with titanium oxide in the molten calcium chloride. The TiO 2 samples placed in the molten salt could be reduced without any electron supply to TiO 2 . In the close vicinity of cathode, TiO 2 could be successfully reduced to -Ti with 1600 mass ppm oxygen. However, the strong stirring of the melt disturbed the calcium distribution near the cathode and the reduction was incomplete. These findings supported the proposed mechanism that Ca deposited on the cathode and it dissolved immediately into the molten salt. The parasite reactions consumed the dissolved Ca quickly, and they suppressed the effective reduction and subsequent deoxidation.

Calciothermic reduction of NiO by molten salt electrolysis of CaO in CaCl2 melt

“…Metal oxides are immersed into a bath of molten salt and electrolyzed by applying electric field. The metallic products are formed at the cathode and the carbonic gases are expelled at the anode [1][2][3][4][5][6][7][8][9][10][11][12][13]. Aside from pure metal production, this process was tried in producing some alloys and intermetallic compounds directly from the oxide mixture [14][15][16][17][18][19], making it an attractive reduction method.…”

“…Aside from pure metal production, this process was tried in producing some alloys and intermetallic compounds directly from the oxide mixture [14][15][16][17][18][19], making it an attractive reduction method. Varieties of salts are employed as the electrolytes, but the salt most largely used is CaCl 2 -based salt because calcium chloride can dissolve up to 20 mol% CaO [20][21][22] and because a small addition of CaO in CaCl 2 was found to improve the rate of reduction and deoxidation [3][4][5][6][7][8][9]12,13].…”

“…OS process speculated that the presence of Ca dissolved in molten salt was responsible for reduction [1][2][3][4][5][6][7][8][9]. The dissolved Ca reacts with titanium dioxide producing metallic titanium and CaO as presented in Eq.1 [1][2][3].…”

“…Namely, in the purely calciothermic reduction of TiO 2 without external electrochemical potential [3], 0.5 mol% CaO in the CaCl 2 melt resulted to the better deoxidation, i.e., the lowest residual oxygen in the reduced metallic titanium was achieved. Therefore, it has often taken as the standard condition in CaO concentration [4][5][6][7][8][9]; however, no experimental optimizations have been given in the concept of OS process. This work aims to examine the CaO concentration that is favourable for reduction and deoxidation of metal oxide in the case of electrolysis in the molten CaCl 2 bath.…”

Rapid reduction of titanium dioxide nano-particles by reduction with a calcium reductant

“…For example, metallic calcium formed electrochemically at a cathode reacts with metal oxides, and reduced metals with a low residual oxygen content can be formed (OS (Ono and Suzuki) Kyoto process). Metallic titanium [13][14][15], niobium [16], nickel [17], and other alloys and intermetallic compounds [18,19] can be formed via the OS process. In addition, the electrochemical decomposition of carbon dioxide gas by an advanced OS process using a solid electrolyte anode has been reported [20,21].…”