Deoxidation Mechanism in Reduced Titanium Powder Prepared by Multistage Deep Reduction of TiO2

Abstract

There are technical bottlenecks in the preparation of metallic titanium powder by conventional thermal reduction of TiO2 with calcium, magnesium, or other metals, such as low efficiency and incomplete deoxidation. Based on the thermodynamic equilibrium characteristics of the step-by-step reduction of TiO2, a comparative study method was used, and the thermodynamic and kinetic differences between thermal reduction reactions of TiO2 with magnesia and calcium were investigated in this paper. Considering the difference in the electronegativity characteristics between magnesium and calcium, a new idea was put forward that the primary reduction product is prepared through a primary reduction process of TiO2 in the form of magnesiothermic self-propagating high-temperature synthesis (SHS), and then the reduced titanium powder is obtained through the primary reduction product for a deep calcium-thermal reduction reaction. The reduction degree and mechanism of TiO2 during the primary magnesium thermal reaction and deoxidation mechanism of primary reduction products in different deep reduction modes were investigated in this paper. The results showed that it is more conducive to undergo complete deoxygenation such that the primary reduction product is first acid impregnated, followed by deep calciothermic reduction. High-purity reduced titanium powder with a final oxygen content of only 0.21 pct and purity greater than 99.0 pct was obtained.