Kinetics of Zirconium Electroreduction on Glassy Carbon in Fluoride Melts

The electrochemical behavior of zirconium ions in melts based on alkaline metal fluorides is studied. The kinetic patterns of the electroreduction of zirconium and aluminum from the KF-AlF3-Al2O3-ZrO2 melts at 750 degrees C are studied by cyclic chronovoltammetry (CV). The influence of the additive content and potential sweep rate on the kinetics of the cathodic process in the melts under non-steady-state conditions is studied. The cathodic discharge currents of aluminum ions are shown to appear in the potential range from -1.6 to -1.7 V relative to the CO/CO2 electrode potential, and a doubled peak (Al) appears at the potential about -1.9 V, which is associated with aluminum electroreduction from different electroactive ions (Al-2 OF62-, AlF4-). The presented dependences are consistent with the earlier obtained results of measurements in the KF-AlF3-Al2O3 melts. When ZrO2 is introduced into the KF-AlF3-Al2O3 melt, a plateau and a discharge peak of electroactive ions appear on the cathodic branch of the CV curves at potentials of -1.4 and -1.7 V, respectively. The presence of two responses is associated with the electroreduction of zirconium ions (platform Zr) and the combined electroreduction of zirconium and aluminum ions (peak Al + Zr) with the formation of the intermetallic compound AlxZr. The electroreduction of zirconium ions at more positive potentials is explained as follows. Of the electroactive ions ZrF (2-)(6)and Al-2 OF(6)(2-)present in the melt, the former has the lowest bonding energy, while zirconium has a higher carbon affinity compared to aluminum at the experimental temperature. Therefore, the depolarization during the electroreduction of zirconium ions on glassy carbon (GC) is higher.