Preparation of High Purity Vanadium Metal for Hydrogen Storage Using the Direct Reduction and Simultaneous Molten Salt Electrolysis

点击翻译按钮获取中文摘要

A New process was developed that the metallic vanadium (V) was prepared by the direct reduction from the molten vanadium oxide melt (V_2O_5). Two steps (A) and (B) were combined: (A) The solid oxides was directly reduced by calcium dissolved in the molten salt, and (B) the by-product CaO was electrochemically decomposed into the metallic calcium. This combination is hereafter called as OS process, which is extended to the molten oxide V_2O_5, in addition to the solid lower oxides.By applying OS process in the molten CaCl_2, the optimization of electrodes arrangement was studied in order to react efficiently with the molten oxide V_2O_5 and Ca existing near the cathode. Mo or V was taken for the cathodic material. The current efficiency decreased when the crucible-type electrode was used. The anodic carbon was set more closely to the cathode, such as in a few mm, and we obtained the excellent quality of vanadium metal containing only 2000 ppm oxygen. The phase transformation during the reduction was studied in addition to the analysis of electrochemical behavior and current efficiency at the various electrode arrangements. The reduction rate corresponded well to the supplied current. A high current efficiency could be achieved at the initial stage of reaction. At the later stage of reduction, however, the deoxidation from the obtained vanadium metal was dominant, and both the current and the current efficiency decreased. The decreasing rate of oxygen content could be expressed in an unique formula against the supplied electric charge over the whole experimental time. This implies that the rate-determining step in OS process is the diffusion of Ca or CaO into the molten CaCl_2 bulk.