Using electro-deoxidation to synthesize niobium sponge from solid Nb₂O₅ in alkali–alkaline-earth metal chloride melts

The method of electro-deoxidation was applied to reduce solid Nb₂O₅ directly to niobium metal, in the form of sponge, in the eutectic CaCl₂–NaCl and BaCl₂–NaCl systems, respectively. The direct electrochemical reduction of solid Nb₂O₅ was achieved by electrolysis in the chloride melts at temperatures between 850 and 950 °C and at a controlled potential of 3.1 V, well below the decomposition potentials of the melts used. The obtained results demonstrated that the method is applicable for preparing niobium sponges directly from solid Nb₂O₅ under the present experimental conditions. The niobium sponge prepared was proven to possess as remarkable superconducting properties. The parameters affecting the rate and the extent of electro-deoxidation were investigated experimentally, including initial particle sizes of the starting Nb₂O₅ powders, compaction pressure, sintering temperature and times, electrolysis temperature and duration, and electrolyte systems. The mechanism by which the Nb₂O₅ pellets were electro-deoxidized to the niobium sponges was also discussed on the basis of the present experimental observations.