Effects of pre-added and in situ formed SiO2 on combustion synthesis of TiB2/mullite composites

AbstractTiB2/mullite composites were produced by self-propagating high-temperature synthesis involving exothermic reduction of B2O3 by Al or both Al and Si. Two reactant mixtures formulated as 7/2Ti + 3B2O3 + B + 6Al + xSiO2 with x = 1·0–3·0 and 29/6Ti + 13/3B2O3 + B + 6Al + ySi with y = 1·5–4·0 were prepared to study the effects of pre-added and in situ formed SiO2 on combustion behaviour and mullite formation. For the SiO2-added samples, the increase of SiO2 improved mullite formation, but the dilution effect of SiO2 and endothermic mullitisation process reduced the combustion temperature and flame velocity. On the other hand, the Si-adopted samples were more exothermic than those with pre-added SiO2 and were favourable for the growth of needle-like mullite grains. Excess amounts of SiO2 (x = 2·5) and Si (y = 3·5) were required for samples to achieve an optimum yield of mullite, and the resultant products were TiB2/mullite composites with a little Al2O3.