Kinetics and mechanism of low-temperature aluminothermic reduction of manganese tantalate

The paper studies the kinetics of low-temperature (840-1180 degrees C) reduction of manganese tantalate (99.4 mass% MnTa2O6, 0.6 mass% Ta2O5, particle size <0.1 mm) with aluminium powder (particle size <0.14 mm) taken in an amount providing a mole ratio of MnTa2O6: Al = 1: 10. Reduction experiments were performed in non-isothermal mode using differential scanning calorimetry at three heating rates. Kinetic analysis of the experimental data was performed by the Friedman and Ozawa-Flynn-Wall methods with optimisation of results by non-linear regression. It is shown that the reduction process corresponds to a combined exothermic peak in the differential scanning calorimetry curve with the temperatures of onset at 890 degrees C and maxima at 940 and 1032 degrees C. At 1180 degrees C, the reduction products are TaAl3, MnAl6-delta, Ta, Mn1+xAl1-x, Mn8.97Al30.03, Mn53.3Al230.8, and Al, while the process can proceed through the formation of intermediate oxides of the MnxTaO4-y type. The process is represented by a scheme that includes three consecutive steps controlled by nth-order chemical reactions. The mathematical model built based on the obtained data sufficiently describes the rate of low-temperature reduction of manganese tantalate with the excess of aluminium and can be used to optimise the technological modes for producing tantalum alloys.