2020 年 61 巻 10 号 p. 1967-1973
A new reduction process for producing titanium (Ti) with an ultra-low oxygen concentration directly from TiO2, employing yttrium (Y) as the reductant, was developed in this study. Several methods for the direct reduction of TiO2 have been proposed to lower the cost of production of Ti. However, none of them have yet been applied industrially. In addition, Y has never been used as a reductant for reducing TiO2 although its reducing ability is the highest among the reductants capable of reducing TiO2 to Ti with low oxygen concentration. In this study, the reduction reactions of TiO2 using Y/Y2O3 equilibrium and Y/YOCl/YCl3 equilibrium, employing various molten salts as solvents, were investigated. TiO2 pellets and metallic Ti pieces were placed in several types of solvents along with sufficient Y and heated at 1300 K for 86 ks. When YCl3 or CaCl2 was used as the solvent, the TiO2 pellets were reduced to metallic Ti. The oxygen concentrations in the Ti pieces after heating in YCl3 and CaCl2 were 90 ± 40 mass ppm O and 350 ± 60 mass ppm O, respectively. However, when NaCl or KCl was used as the solvent, a small amount of metallic Ti and a large amount of complex oxides were obtained. It is considered that the reduction reaction did not proceed sufficiently owing to the low solubility of the oxide ions in molten salts. It was experimentally demonstrated that Ti with an ultra-low oxygen concentration (100 mass ppm O or less) can be directly produced from TiO2 by using Y as the reductant in an appropriate solvent. This method is expected to lead to the development of a new industrial process for the production of Ti with an ultra-low oxygen concentration directly from its ore.