固体TiO<sub>2</sub>の溶融マグネシウムによる還元機構と反応の促進

Abstract

The possibility of direct reduction of TiO2 by molten magnesium has been investigated using TiO2 single crystals and powders. First, reduction experiments were carried out using TiO2 single crystals at 1173 K for up to 8 h, resulting in formation of two layers consisting of oxide phases with different Mg and Ti concentrations between magnesium and TiO2, in which layers TiO2 was reduced only to TiO0.5 as a maximum and there was no metallic titanium obtained. The thicknesses of both the oxide layers increased according to the parabolic rate law, and Mg is reported to have diffusivity greater than the others, suggesting that the reduction rate of TiO2 is controlled by the diffusion of Mg across the oxide layers. Second, reduction experiments were carried out using TiO2 powers having 45 and 100 μm diameters at 1173 K for up to 48 h, resulting in reduction of TiO2 to form metallic titanium, TiO0.5 and TiO, indicating the effect of change in figuration of TiO2 from single crystal to powder. However, difference in powder size did not appear in the degree of reduction presumably due to sintering effect during reduction. Finally, reduction experiments were carried out using TiO2 powers having 45 μm diameters with additions of MgCl2 at 1173 K for 30 h because MgCl2 is miscible with MgO. TiO2 was reduced to form only metallic titanium and TiO0.5, without TiO remaining as titanium oxide, suggesting the removal effect of MgO by MgCl2 which may allow continuous reduction on the TiO2 surface. Consequently, it has been found that additions of MgCl2 are effective to promote reduction of TiO2 by molten magnesium.