Solid oxide membrane technology for environmentally sound production of titanium

Abstract

Despite its attractive properties, titanium is limited in use by its high price, due to the cost of smelting and processing the ore. The solid oxide membrane (SOM) process aims to consolidate most of the processing steps required for conventional titanium production into a single step, making it an energy efficient and cost effective method for producing CP billet and ingot and possibly also powders used to make titanium alloys. In the SOM process experiment, a steel crucible contains MgF₂–CaF₂–TiO₂ flux; an inert metal/carbon rod serves as the cathode; an oxygen ion conducting yttrium stabilised zirconia (YSZ) membrane in the form of a one end closed tube contains either a liquid metal that acts as the anode or a liquid MgF₂–CaF₂ ionic flux that connects the YSZ membrane to an anode. During electrolysis, titanium ions are reduced at the cathode while the oxygen ions pass through the YSZ membrane and are oxidised at the anode by a reducing agent, hydrogen gas or carbon, forming steam or CO(g) respectively. To date, a suitable MgF₂–CaF₂–TiO₂ flux has been selected and an optimum operating temperature has been determined. Several electrolysis experiments have been performed. As expected, lower valence deposits of titanium oxides have been witnessed at the cathode before depositing pure titanium. Continuing work will aim to extend the electrolysis time to pass enough charge to produce a significant amount (100 g) of titanium at the cathode.