Semi-continuous Production of Niobium Powder by Magnesiothermic Reduction of Nb₂O₅

Abstract

An electronically mediated reaction (EMR) has been explored to produce a niobium powder semi-continuously by the magnesiothermic reduction of niobium oxide. Nb₂O₅ feedstock and reductant magnesium alloy were isolated electronically in a molten CaCl₂ bath at 1173 K . The feed was freshly recharged twice, but the bath was reused without replenishment during three repeated tests, providing an external path for electron flow. The current flow through the external path between the feed (cathode) and the reductant (anode) was monitored. A small current between 0.05 and 0.1 A was measured in the external circuit. A niobium powder was readily obtained, but its purity decreased from 93 to 82% Nb as the reduction number increased. This, however, demonstrated the possibility of semi-continuous production of niobium powders by the EMR without the direct physical contact between the reactants. The mechanism of the magnesiothermic reduction of Nb₂O₅ in the molten salt was discussed, using an isothermal chemical potential diagram.