Phase Formation during Aluminothermic Reduction of Titanium from Its Oxides with the Anatase and Rutile Structures

Low-temperature phase formation processes (below 1270–1450°C) underlying aluminothermic reduction of titanium from different TiO2 polymorphs—stable rutile and metastable anatase—have been studied during continuous heating and isothermal heat treatment. Interaction between the components has been investigated at TiO2/Al molar ratios of 0.23 and 0.43 using thermal analysis and X-ray diffraction. The results demonstrate that, in the case of continuous heating of anatase + aluminum powders with TiO2/Al = 0.43, the reduction process begins at a temperature of 943°C and does not reach completion up to 1270°C, resulting in the formation of the intermetallic phase Al3Ti, Al2O3, and intermediate titanium oxides (Ti0.78O0.937 and (Ti0.99Al0.01)2O3). Increasing the fraction of aluminum in the mixture (TiO2/Al = 0.23) increases the degree of reduction of titanium, which shows up as an increase in the amount of intermetallic phases (Al3Ti, Al2Ti, Al1.1Ti0.9, and AlTi3) in the reduction products and a decrease in the amount of intermediate titanium oxides. Rutile has been shown to have low reactivity: heating of rutile + aluminum mixtures to 1450°C leads to the formation of many intermediate titanium oxides along with a small amount of Al3Ti and AlTi3. The results have been confirmed by isothermal heat treatment (1400°C, 60 min) of mixtures of anatase and rutile with aluminum. The anatase-to-rutile polymorphic transformation during heating in flowing argon has been shown to occur in the range 622–913°C. During the reduction process, molten aluminum inhibits the phase transition of anatase, but its reactivity remains higher than that of rutile