Enhancing the ignitability of the Al–TiO2–B2O3 powder mixture through intensive vibratory ball milling (C:P12)

Alumina-TiB2 is a hard ceramic composite with applications in aviation, aerospace and wear resistant tools. It can be manufactured in-situ through a highly exothermic aluminothermic self-sustaining reaction from the starting materials of Al, TiO2 and B2O3. In this paper, the effect of vibration ball milling on the particle size reduction and the reactivity enhancement of the Al–TiO2–B2O3 powder mixture is examined by XRD, SEM, EDS, DTA and particle analysis techniques. Measures for combating the stoichiometric inconsistencies deriving from the tendency of B2O3 to absorb atmospheric water, giving boric acid H3BO3, are implemented. Characterisation of the milled samples display Al microparticles with d(0.9) below 64 μm, coated with nano-particles of TiO2 and B2O3, with particle sizes up to 600 nm. Differential thermal analysis reveals that ignition is feasible for all of the milled mixtures, unlike the un-milled one. It also presents that extensive milling results in a reduction in the ignition temperature of the reactant mixture to 925 °C for the 5 h-30Hz milled sample, from the previous 982 °C recorded for the 1 h–20Hz milled sample. The in-situ synthesised Al2O3–TiB2 matrix deriving from the 5 h-30Hz milled sample, gives less of the unwanted Al5BO9 phase and improved skeletal and bulk densities, by 0.15 g/cc and 0.1 g/cc respectively, compared to the respective composite deriving from un-milled reactants powder mixture.