Understanding the Magnesiothermic Reduction of Intermediate TiNb₂O₇ to Produce Ti-Nb Alloys

A novel approach to directly produce Ti-Nb alloys through direct magnesiothermic reduction from intermediate TiNb₂O₇ (TNO) is demonstrated. Using a combination of X-ray diffraction, scanning electron microscope–energy dispersive spectroscopy, and scanning transmission electron microscopy, the observed phases, chemical composition, and crystal structure could be identified and the reaction pathway determined. Although thermodynamically favorable, the reductions carried out between 700°C and 900°C at various Mg/TNO stoichiometric molar concentrations showed 1.5 times the stoichiometric molar ratio (mass ratio Mg/TNO of 10.5) to produce Ti-Nb alloy products, but complete reduction was not possible owing to the depletion of Mg from vaporization and reactions. Excess amounts of Mg at 5 times the stoichiometric molar ratio (mass ratio Mg/TNO of 35) resulted in full reduction of the TNO powders to produce Ti-Nb alloys without Ti-Nb-Mg-O intermediate oxide phases. A comparison of the magnesiothermic reduction of the individual components, including TiO₂, Nb₂O₅, and TNO, indicated the reduction of TiO₂ to be complex and limiting, with reduction significantly easier for Nb₂O₅ and TNO at higher temperatures and excess Mg contents.