Understanding the Magnesiothermic Reduction Mechanism of TiO₂ to Produce Ti

Titanium dioxide (TiO₂) powders in the mineral form of rutile were reduced to metallic and an intermediate phase via a magnesiothermic reaction in molten Mg at temperatures between 973 K and 1173 K (700 °C and 900 °C) under high-purity Ar atmosphere. The reaction behavior and pathway indicated intermediate phase formation during the magnesiothermic reduction of TiO₂ using XRD (X-ray diffraction), SEM (scanning electron microscope), and TEM (transmission electron microscope). Mg/TiO₂ = 2 resulted in various intermediate phases of oxygen containing titanium, including Ti₆O, Ti₃O, and Ti₂O, with metallic Ti present. MgTi₂O₄ ternary intermediate phases could also be observed, but they were dependent on the excess Mg present in the sample. Nevertheless, even with excessive amounts of Mg at Mg/TiO₂ = 10, complete reduction to metallic Ti could not be obtained and some Ti₆O intermediate phases were present. Although thermodynamics do not predict the formation of the MgTi₂O₄ spinel phase, detailed phase identification through XRD, SEM, and TEM showed significant amounts of this intermediate ternary phase even at excess Mg additions. Considering the stepwise reduction of TiO₂ by Mg and the pronounced amounts of MgTi₂O₄ phase observed, the rate-limiting reaction is likely the reduction of MgTi₂O₄ to the Ti_tO phase. Thus, an additional reduction step beyond thermodynamic predictions was developed.