Self-propagating high-temperature synthesis of Al2O3-TiC-Al composites by aluminothermic reactions

Al2O3-TiC-Al composites were fabricated by self-propagating high-temperature synthesis process using aluminothermic reactions with titania, aluminum, and graphite powders. As the molar ratio x of the excessive aluminum in the reactants increases, the adiabatic temperature of the reaction and the melting rate of alumina in the products obviously decrease according to thermodynamics. This reaction is theoretically presumed to be ignited at preheat temperature of 900 K even though x is up to 13 mole. The experimental results revealed that the critical molar ratio of excessive Al, which the combustion reaction can self-sustain, is 7.66 mole with a preheat temperature of 400-500 K. The excessive aluminum favors to fill in the pores of the products, and a cylindrical Al2O3-TiC-Al composite with a relative density of 70% can be obtained, and its tensile strength is higher ten times than that of the Al2O3-TiC composite. Moreover, TiC and Al2O3 grains in the composites are fined as the excessive aluminum increases. Although the excessive aluminum does not take part in the combustion reaction, it strongly affects combustion process and microstructures of the products. (C) 2001 Kluwer Academic Publishers.