Study of the Electrochemical Reduction of Zr[sup 4+] Ions in Molten Alkali Fluorides

The electrochemical behavior of Zr 4+ in potassium-free fused alkali fluorides has been studied in the temperature range of 773-1123 K.With an inert tungsten or molybdenum electrode, a well-defined oxydo-reduction wave was observed during cyclic voltammetry experiments.The reduction of Zr 4+ is a single four-electron reversible step, and the process is diffusion controlled.Chronopotentiometry measurements give rise to the diffusion coefficient values of Zr 4+ ions.For instance, a value 2.92 ϫ 10 -5 cm 2 s -1 was found at 1010 K.The reduction of Zr 4+ ions was also studied using a nickel electrode for which Ni-Zr alloys formation was pointed out as revealed by cyclic voltammetry.The analysis of these deposits by scanning electron microscopy ͑SEM͒ and energy dispersive X-ray showed the presence of a multilayered Ni-Zr alloy with different Zr contents.On graphite electrodes, zirconium carbides have been evidenced on cyclic voltammograms and the formation of Zr metal was observed by SEM.