Precise fabrication of Ti2O from TiO2 by Al reduction towards potentially lower-cost Ti metal powder production

Abstract

Titanium is a highly valued material. Developing a lower-cost titanium (Ti) metal powder production process, potentially substituting the conventional Kroll-HDH method, has challenged the titanium community for decades. The ease of aluminum forming alloys with titanium and the strong chemical affinity of titanium to oxygen rule out the possibility of fabricating pure Ti metal directly by aluminum reduction of TiO2. Based on the demonstrated enhanced deoxidation of Ti using Mg metal, this paper proposes an Al–Mg combined stepwise reduction of TiO2 to fabricate Ti metal powder. Critical challenges overcome in this research include predicting reaction thermodynamics and preparing Ti2O intermediate by Al reduction of TiO2 without significant Al alloying, which is made possible by forming mild-acid soluble Ca12Al14O32Cl2 byproduct. Various Al reduction conditions were investigated and optimized. To the best of our knowledge, it is the first report to fabricate Ti2O powder by Al reduction of TiO2 with a highly stable chemical composition. The difficulty of sintering the Ti2O intermediate before Mg deoxidation to reduce the surface oxygen contribution is mitigated by mixing a certain amount of low-oxygen titanium powder with the Ti2O powder. This allows the densification temperature to be lowered from 1400 °C for sintering pure Ti2O powder to 1100 °C. Even with as much as around 15 wt% oxygen, the sintered powder can be effectively deoxidized by Mg with the help of hydrogen. A titanium metal powder with an oxygen content of 0.134 wt%, an Al content of 0.123 wt%, and other impurities meeting the standard of pure titanium metal powder (GB/T 34486-2017 FTA1) is successfully prepared by the Al reduction-Mg deoxidation combined process. It is a promising alternative for producing titanium metal powder and its derivatives.