Deoxygenation is in high demand in the titanium industry. This research was carried out to experimentally determine the oxygen removal limits by the novel hydrogen-assisted Mg deoxygenation method. Spherical Ti and Ti-6Al-4V (or TC4, Ti64) powders with around 2.2 wt% oxygen were prepared for the deoxygenation research. The deoxygenation kinetics were modeled based on a non-steady-state radial diffusion. The results show that in the β phase region, the time to reach the equilibrium is slightly affected by the initial oxygen content in titanium, but is strongly influenced by the particle size. The reliance of the equilibrium duration on the diffusion coefficient is stronger when the particle size is larger. Guided by the kinetic prediction, deoxygenation experiments were carried out. Under a 1 atm pure H 2 atmosphere, the deoxygenation limits by Mg for pure Ti are 252 ppm at 700 °C, 289 ppm at 750 °C, and 554 ppm at 800 °C, and for TC4 are 296 ppm at 750 °C, 371 ppm at 800 °C, and 743 ppm at 850 °C, consistent with the thermodynamics that a lower temperature possesses a more potent driving force for deoxygenation. These data have clearly demonstrated the strong deoxygenation capability of the hydrogen-assisted Mg deoxygenation method.
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 TiO 2 . Based on the demonstrated enhanced deoxidation of Ti using Mg metal, this paper proposes an Al–Mg combined stepwise reduction of TiO 2 to fabricate Ti metal powder. Critical challenges overcome in this research include predicting reaction thermodynamics and preparing Ti 2 O intermediate by Al reduction of TiO 2 without significant Al alloying, which is made possible by forming mild-acid soluble Ca 12 Al 14 O 32 Cl 2 byproduct. Various Al reduction conditions were investigated and optimized. To the best of our knowledge, it is the first report to fabricate Ti 2 O powder by Al reduction of TiO 2 with a highly stable chemical composition. The difficulty of sintering the Ti 2 O intermediate before Mg deoxidation to reduce the surface oxygen contribution is mitigated by mixing a certain amount of low-oxygen titanium powder with the Ti 2 O powder. This allows the densification temperature to be lowered from 1400 °C for sintering pure Ti 2 O 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.
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