Aluminum borate in the combustion synthesis of alumina/boride composite

The formation mechanism of aluminum borate in the combustion synthesis of Al2O3/B4C composite with Al, B2O3, and C as starting materials is proposed. Based on the formation mechanism, several approaches taken to eliminate them are discussed. The unconverted B2O3 is the major cause of the formation of 9Al2O3 · 2B2O3 when the reaction proceeds in the SHS mode. The amount of 9Al2O3 · 2B2O3 formed is very sensitive to the excess B2O3 to the stoichiometry 4Al + 2B2O3 + C and influenced by the size of B2O3 powder. The high dispersion of the reactants is helpful in prompting the thermite reaction to consume B2O3 and hence inhibiting the aluminum borate formation.