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

The stability of indium chloride and oxide as well as the electrochemical b ehaviour of indium ions have been studied in the equimolar CaCl2-NaCl melt at 550 degrees C by X-ray diffraction (XRD) and different electrochemical t echniques, using molybdenum and tungsten wires as working electrodes. Volta mmetric and chronopotentiometric studies showed signals attributed to the p resence of three oxidation states of indium, i.e. 0, I and III. The standar d potential of the redox couples, as well as the solubility products of ind ium oxides have been determined, showing that In(III) ions are completely r educed 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) + O<SUP>2- </SUP>These results have allowed the construction of E-pO(2-) equilibrium d iagrams 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 correspondin g 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.