Formation of Ni-Zr Alloys in Molten Fluorides

Abstract

The electrochemical behavior of Zr4+ was investigated in LiF-NaF between 923 and 1123 K. With an inert tungsten or molybdenum electrode, a well-defined oxydo-reduction wave was observed during cyclic voltammetry experiments. The reduction of Zr4+ is a single four-electron step and quasi-reversible, and the process is diffusion-controlled. Chronopotentiometry was used to measure the diffusion coefficient of Zr4+ ions. For instance, a value 1.54 × 10-5 cm2 s-1 was found at of at 979 K. The reduction of Zr4+ ions was also studied using nickel electrode. In that case, Ni- Zr alloys were formed as pointed out on cyclic voltammograms which exhibit several characteristic peaks. SEM and EDX analyses have revealed the presence of a multi-layered Ni-Zr alloy deposited film on Ni electrode. At -1.65 V vs Ni/Ni2+, three successive layers were pointed out, corresponding to three different Ni-Zr alloy compositions.