Hydrogen assisted magnesiothermic reduction of TiO2

The development of low cost titanium metal production processes has challenged the Ti research and industrial communities around the world for decades. The strong affinity of titanium to oxygen dictates that it is very difficult to produce low-oxygen Ti metal from TiO2 directly. In this paper, a hydrogen assisted magnesiothermic reduction (HAMR) process for producing Ti metal powder from TiO2 powder at relatively low temperatures (<= 750 degrees C) is established. The overall approach is based on the thermodynamic tuning of the relative stability of MgO versus that of Ti-O solid solutions by temporarily alloying the system with hydrogen. It is shown that Ti-H-O solid solutions are less stable than their corresponding Ti-O solid solutions, which changes the reaction of Mg with Ti-O from being thermodynamically unfavorable to being favorable. The key steps for producing pure Ti metal powder from TiO2 involve Mg reduction of TiO2 in a hydrogen atmosphere which produces porous TiH2, a heat treatment procedure to consolidate the powder and reduce specific surface area of the powder, and the final step to deoxygenate the powder using Mg in a hydrogen atmosphere to further reduce the oxygen content. This paper systematically examines the changes of oxygen content, phase transformations, and the evolution of the morphology of the particles during the entire process. The results show that this approach has great potential to be a viable method for the production of low-oxygen Ti metal powder from TiO2. In addition, the effect of hydrogen on the oxidation of Ti powder is analyzed using XPS, which reaffirms that titanium hydride is more impervious to surface oxidation than Ti metal, another crucial advantage of using hydrogen atmosphere. (C) 2016 Elsevier B.V. All rights reserved.