Production of Niobium Powder by Preform Reduction Process Using Various Fluxes and Alloy Reductant

Abstract

In the previous study of the authors, a preform reduction process (PRP) based on the magnesiothermic reduction of a feed preform containing niobium oxide (Nb₂O₅) was established with the aim of minimizing contamination during the reduction process, and its effectiveness in producing fine niobium powder was demonstrated. In this study, various species of fluxes (e.g., CaCO₃, CaCl₂, Na₂CO₃, and NaCl) were tested to find the optimum conditions for producing a homogeneous powder. Feed preform in the form of plates was fabricated by mixing Nb₂O₅ powder, flux and binder. The sintered solid preform containing Nb₂O₅ with various flux compositions was placed in a stainless steel container, and reacted with magnesium vapor at a constant temperature ranging between 1 073 and 1 273 K. Niobium powder with a purity of 99 mass% was recovered from the reduced preform by acid leaching. When CaCO₃ or CaCl₂ flux with cationic molar ratio X_Cat./Nb=1/5 to 1/2 was used, a homogenous fine powder, around 1 μm in diameter, was obtained. Furthermore, an alloy reductant was used to decrease the activity of magnesium reductant with the aim of preventing nickel contamination. The use of an alloy reductant is found to be effective in eliminating the deposition of excess reductant on the preform and on other reaction components. It was found that the particle size of niobium powder can be reduced by using an Mg-Ag alloy instead of pure magnesium.