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.