Voltammetric Studies of the Oxygen-Titanium Binary System in Molten Calcium Chloride

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Abstract
Cyclic voltammetry was applied to study the O-Ti binary system in pre-electrolyzed (2.7-3.0 V) molten CaCl2CaCl2 at 900°C. Before melting, the salt was thermally dried in air, following a four-stage heating program (60°C/h, 1 h at 90°C, 10°C/h, 4 h at 300°C) to minimize hydrolysis. The O-Ti system was represented by oxide-scale-coated titanium that was prepared by heating commercially pure titanium in air at 700°C. The voltammograms exhibited three reduction processes at electrode potentials more positive than that of the reduction of calcium cation. Two of these, at less negative potentials, could be attributed to the reductions of TiO2TiO2 to Ti2O3,Ti2O3, and TiO to Ti metal, respectively. The Ti2O3Ti2O3 was found to disproportionate into TiO2TiO2 and TiO. The third process occurred at a more negative potential, but still more positive than that of calcium cation reduction, and was proven to be the cathodic ionization of dissolved oxygen from the metal phase. It was also found that for partially reduced oxide scale, various calcium titanates could form under conditions that promote reaction of CaO with, or calcium cation intercalation into, the oxide scale. © 2002 The Electrochemical Society. All rights reserved.

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