Electrochemical behaviour of indium ions in molten equimolar CaCl2-NaCl mixture at 550°C

The stability of indium chloride and oxide as well as the electrochemical behaviour of indium ions have been studied in the equimolar CaCl2-NaCl melt at 550 degrees C by X-ray diffraction (XRD) and different electrochemical techniques, using molybdenum and tungsten wires as working electrodes. Voltammetric and chronopotentiometric studies showed signals attributed to the presence of three oxidation states of indium, i.e. 0, I and III. The standard potential of the redox couples, as well as the solubility products of indium oxides have been determined, showing that In(III) ions are completely reduced to monovalent indium by the indium metal according to the reaction: In(III) + 2 In <-> 3 In(I) and that In2O is a strong oxide donor according to the reaction: In<INF>2</INF>O (s) --> 2 In(I) + O2- These results have allowed the construction of E-pO(2-) equilibrium diagrams summarising the properties of In-O compounds. The electrodeposition of indium was uncomplicated at Mo and W electrodes. Very good adherence of liquid indium to the electrode materials was observed, with the formation of Na-In alloys at highly reducing potentials, and there was no evidence of indium dissolution into the melt. Moreover, the voltammograms corresponding to the electrochemical In(III)/In(I) exchange were well defined. The two electrochemical steps were found to be quasi-reversible, and the values of the kinetic parameters, k(o) and alpha, for both reactions, as well as the diffusion coefficients, D-ln(m) and D-ln(I) were calculated.