Voltammetry of titanium dioxide in molten calcium chloride at 900°C

The cathodic deoxygenation. of TiO2 was studied using linear sweep and cyclic voltammetry in pre-electrolyzed molten CaCl2 at 900 degrees C. Continuous TiO2 films 10 mu m thick were thermally formed in air at 700 degrees C on commercial purity titanium rods. Four cathodic processes were observed on a TiO2 working electrode at potentials less negative than that for calcium formation arising from electrolyte decomposition. Two initial reduction processes occurring at potentials 300 mV negative of the TiO2 open-circuit potential were attributed to the deoxygenation of TiO2 to Ti3O5 and Ti2O3, and subsequent reduction of the remaining Ti3O5 to Ti2O3. The concurrent increase in local oxide concentration exceeded the solubility product and caused the formation of calcium titanates. At potentials 1100 mV more negative than the open circuit potential (similar to 500 mV positive of the potential for unit activity Ca formation), two peaks were observed; one corresponding to the decomposition of the titanates and Ti2O3 to TiO, and the other of TiO to metallic titanium with dissolved oxygen. The removal of dissolved oxygen was found to occur at potentials near to that for calcium formation. Material was characterized before and after cyclic voltammetry using scanning electron microscopy, X-ray energy dispersive spectroscopy and X-ray diffraction. (c) 2005 The Electrochemical Society. All rights reserved.