Continuous Production of Bi–Ti Alloys by Magnesiothermic Reduction of TiCl₄ for a New Smelting Process of Ti

Abstract

A new smelting process of Ti via Bi–Ti liquid alloy is proposed, which comprises reduction of TiCl4 by Bi–Mg alloy, enrichment of Ti in Bi–Ti alloys, and vacuum distillation of the alloys. In this study, the continuous reduction of TiCl4 by Bi–Mg alloys and vessel materials for the reduction step were investigated. Firstly, we demonstrated the reduction of TiCl4 by Bi–Mg alloys and the subsequent recovery of Bi–Ti liquid alloys and MgCl2 repeatedly. As the result, the alloys containing 5.2–7.4 mol% of Ti were obtained. However, it was found that the reduction rate of TiCl4 by Bi–Mg alloys is much slower than that by pure Mg because of MgCl2 layer formed on the alloys, slow mass transfer of Mg in the alloy, and small activity of Mg. For fast reduction of TiCl4, it is required to inject TiCl4 into Bi–Mg alloys. Secondly, we kept Bi–10 mol% Ti alloys in stainless steel, soft steel, and Mo crucibles at high temperatures, and measured solubility of each metal in the alloys. The solubility of Mo in the alloy at 900℃ was 220 ppm, and elution from stainless steels and soft steel was dramatically suppressed at 500℃. However, it was found that most Mo in the alloy remains in Bi9Ti8 at the segregation cell. To decrease Mo content in Ti product, it is required that the vessel is cooled to lower temperatures than 900℃ or the shorter time of contact between Mo and liquid alloys is desired.