Reduction of titanium and other metal oxides using electrodeoxidation

Abstract

Many reactive and refractory metals are currently produced industrially by reducing their compounds, including oxides, using a more reactive metal. In some cases, where there is substantial oxygen solubility in the metal, the oxygen is first removed by carbochlorination followed by reduction. Titanium and zirconium are made by reduction of the volatile tetrachlorides by magnesium. The processes consist essentially of two reduction steps: reducing magnesium chloride to magnesium metal and then reduction of the metal compound; this makes the overall reduction process relatively expensive. Electrodeoxidation is very simple in that the oxide to be reduced is rendered cathodic in molten alkaline earth chloride. By applying a voltage below the decomposition potential of the salt, it has been found that ionisation of oxygen is the dominant cathode reaction, rather than alkaline earth metal deposition. In the laboratory, this technique has been applied to reduce a large number of metal oxides to the metals, including titanium, zirconium, chromium, niobium, tantalum, uranium and nickel. Furthermore, when mixed oxides are used as the cathode, alloys or intermetallic compounds of uniform composition are obtained. This may offer advantages over conventional technology for those alloys that are difficult to prepare at present, owing to differences in either density or vapour pressure.