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Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride

Abstract

Many reactive metals are difficult to prepare in pure form without complicated and expensive procedures1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18. Although titanium has many desirable properties (it is light, strong and corrosion-resistant1), its use has been restricted because of its high processing cost. In the current pyrometallurgical process—the Kroll process4,5—the titanium minerals rutile and ilmenite are carbo-chlorinated to remove oxygen, iron and other impurities, producing a TiCl4 vapour. This is then reduced to titanium metal by magnesium metal; the by-product MgCl2 is removed by vacuum distillation. The prediction that this process would be replaced by an electrochemical route6,7,8,9,10 has not been fulfilled; attempts involving the electro-deposition of titanium from ionic solutions have been hampered by difficulties in eliminating the redox cycling of multivalent titanium ions and in handling very reactive dendritic products6,7,8,9,10. Here we report an electrochemical method for the direct reduction of solid TiO2, in which the oxygen is ionized, dissolved in a molten salt and discharged at the anode, leaving pure titanium at the cathode. The simplicity and rapidity of this process compared to conventional routes should result in reduced production costs and the approach should be applicable to a wide range of metal oxides.

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Figure 1: Cyclic voltammograms of titanium foils in molten CaCl2.
Figure 2: Reduction of titanium oxide scale to titanium metal.
Figure 3: Electrolytic cells for the reduction of TiO2 pellets.
Figure 4: Reduction of the TiO2 powder to titanium metal.

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Acknowledgements

This research was sponsored by the EPSRC. T.W.F. first suggested the electrochemical deoxidation of titanium metal. G.Z.C. was the first to observe that it was possible to reduce thick layers of oxide on titanium metal using molten salt electrochemistry. D.J.F. suggested the experiment, which was carried out by G.Z.C., on the reduction of the solid titanium dioxide pellets. M. S. P. Shaffer took the original SEM image of Fig. 4a.

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Correspondence to Derek J. Fray.

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Chen, G., Fray, D. & Farthing, T. Direct electrochemical reduction of titanium dioxide to titanium in molten calcium chloride. Nature 407, 361–364 (2000). https://doi.org/10.1038/35030069

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