Hydrogen Assisted Magnesiothermic Reduction of Y-doped, Nanocrystalline TiO2

Abstract

XRD, SEM, and Particle Size Analysis was performed on nanocrystalline Titanium Dioxide powders synthesized via sol-gel methods (specifically: solvothermolysis of Titanium Butoxide). The use of solgel TiO2 as a feedstock in the initial stages of the Hydrogen Assisted Magnesiothermic Reduction (HAMR) process was investigated for the production of lowoxygen Titanium metal. The addition of dopant rareearth element Y was investigated to determine if such species affect the HAMR process. The evolution of HAMR intermediate and product phases in response to the reduction parameters of temperature, duration, and Hydrogen partial pressure was studied with XRD and SEM techniques. The literature-studied HAMR phase-transition pathway was confirmed by XRD, with early formation of magnesium titanite phases that subsequently decreased with the formation of greater levels of α-Ti (with dissolved oxygen in solid solution) or Ti2O phases. The presence of two distinct magnesium titanites were observed to be depth-dependent, with leeching experiments demonstrating higher levels of Mg2TiO4 at particle surfaces and higher levels of MgTiO3 within particle cores. Traces of β-Ti were observed, indicating occasional extensive deoxygenation of TiO2. Evidence that Y-doping may have accelerated the HAMR process was observed in powders with similar size distributions. Particle cross-sections demonstrated a significant departure from the literature morphologies, with significant interior remodelling and a lack of distinct phase migration fronts. Microstructure differences were posited to arise from low-temperature formation of the precursor, nanocrystalline TiO2. Further investigation and modelling of the observed, new microstructures, contrasted against literature investigations of highly-crystalline TiO2, was identified as a potential area of novelty for future work. A leeching procedure was established to inform laterstage HAMR work, and experiment improvement recommendations were made for future work.