Zirconium behavior in molten LiCl-KCl eutectic

Some oxidation states (0, 11, 12, and 14) of zirconium exist in a LiCl-KCl eutectic system over the temperature range 450-550degreesC, and the behavior is complicated. In cyclic voltammograms at 500degreesC, a cathodic peak was observed at about 21.2 V vs. Ag/AgCl reference electrode, which might be due to the reduction of Zr(IV) to ZrCl and zirconium metal. Two anodic peaks might correspond to the oxidation of ZrCl and zirconium metal, respectively. The electrolysis at a cathode potential of about -1.1 V yielded a nodular deposit identified as ZrCl, which appeared to be a metastable compound in this system. When the potential was sufficiently negative (i.e., <-1.35 V), zirconium metal was obtained. The deposited zirconium metal was fine black powder, and adhesion to the cathode wire was poor. In the presence of cadmium metal at the cathode, an intermetallic compound that might be Cd3Zr was obtained. The collection efficiency of zirconium is improved using cadmium because the adhesion of the intermetallic compound was much better. Zirconium metal reacted with Zr(IV) to give Zr(II) whose solution was light brown, and Zr(II) was easily disproportionated into Zr(IV) and zirconium metal. The anodic dissolution test indicated that the zirconium metal primarily dissolved into the electrolyte salt as Zr(IV). The Zr(II)/Zr(IV) ratio seemed to be very low and to increase with increasing temperature. (C) 2004 The Electrochemical Society.