A FUNDAMENTAL-STUDY ON PREPARATION OF AL3TI POWDERS BY CALCIOTHERMIC REDUCTION OF OXIDES

The fine Al3Ti compound powders were produced directly from the oxide mixtures of TiO2 and Al2O3 by the calciothermic reduction using CaH2. This procedure consists of three steps: raw oxide blending, co-reduction and leaching. After the reduction of the oxide mixture with various compositions, CaAl2 and Ca12Al14O33 were often formed as the by-product and transient oxide, respectively. They were removed by leaching in the acid aqueous solution. The obtained Al3Ti powders was a few micrometer in particle size and contained about 2500 mass ppm oxygen. The isothermal annealing of the specimens in the Ti-Al-Ca system at 1273 K showed that Al3Ti is in equilibrium with CaAl2 and the Al-rich Al-Ca liquid at 1273 K. Based on these experimental phase equilibria and on the thermodynamical data in Al-Ca system, the activities of Ca and Al and the phase diagrams at 1273 K were evaluated and revised. By using them the suitable compositions and conditions for the co-reduction were discussed and proposed.