Electrochemical Synthesis of Rare-Earth Hexaborides in Chloride-Oxide Melts

Chloride-oxide melts used in electrosynthesis of calcium and rare-earth borides have been studied by Raman and IR spectroscopies. The results, in combination with analysis of data in the literature, have been used to identify the mechanism underlying the sequential transition of solid lanthanide oxides to an ionic form in molten calcium chloride. Using chronopotentiometry and cyclic voltammetry, we have demonstrated that the boride formation is a two-step process. An overall reaction has been proposed that describes the electrochemical boride synthesis process. The proposed mechanism is consistent with the laws of chemical thermodynamics and allows one to describe the exchange and electrode reactions involved.