Electrochemical studies on the redox behaviour of zirconium in molten LiCl-KCl eutectic

Electrochemical studies on zirconium chloride in molten LiCl-KCl eutectic were carried out in presence and absence of Zr metal, in the temperature range 773-848 K using transient techniques such as cyclic voltammetry, square wave voltammetry, convolution voltammetry and chronopotentiometry. Two cathodic peaks due to Zr 4*/Zr* and simultaneous reduction of Zr2+/Zr and Zr2+/Zr+ were observed in the cyclic voltammograms obtained in the absence of Zr metal. When cyclic voltammetry was carried out in presence of Zr metal, a cathodic peak corresponding to Zr+/Zr was observed which shifted to more cathodic potentials and that due to Zr4+/Zr2+ was not observed due to the disproportionation reaction involving Zr and Zr4+. However, oxidation of Zr2+ to Zr4+ was observed in the cyclic voltammograms obtained at higher temperatures. The cyclic voltammograms were complicated by the adsorption of the Zr2+ at the tungsten working electrode. A nucleation overpotential was observed in the cyclic voltammograms of LiCl-KCl-ZrCl4 in presence of Zr metal. Chronopotentiometric transients obtained in the absence of Zr metal showed two transition time plateaus corresponding to Zr4+/Zr2+ and Zr2+/Zr reductions whereas in presence of Zr metal transition time plateaus corresponding to Zr2+/Zr and Zr+/Zr reductions were also observed. Chronopotentiometry also showed that the electrode process due to Zr+/Zr was irreversible. There was no evidence of Zr3+ species in any of the cyclic voltammograms. (C) 2008 Elsevier B.V. All rights reserved.