Formation of TiB(2)–MgAl(2)O(4) Composites by SHS Metallurgy

TiB(2)–MgAl(2)O(4) composites were fabricated by combustion synthesis involving metallothermic reduction reactions. Thermite reagents contained Al and Mg as dual reductants and TiO(2) or B(2)O(3) as the oxidant. The reactant mixtures also comprised elemental Ti and boron, as well as a small amount of Al(2)O(3) or MgO to serve as the combustion moderator. Four reaction systems were conducted and all of them were exothermic enough to proceed in the mode of self-propagating high-temperature synthesis (SHS). The reaction based on B(2)O(3)/Al/Mg thermite and diluted with MgO was the most exothermic, while that containing TiO(2)/Al/Mg thermite and Al(2)O(3) as the diluent was the least. Depending on different thermites and diluents, the combustion front temperatures in a range from 1320 to 1720 °C, and combustion wave velocity from 3.9 to 5.7 mm/s were measured. The XRD spectra confirmed in situ formation of TiB(2) and MgAl(2)O(4). It is believed that MgAl(2)O(4) was synthesized through a combination reaction between Al(2)O(3) and MgO, both of which can be totally or partially produced from the metallothermic reduction of B(2)O(3) or TiO(2). The microstructure of the TiB(2)–MgAl(2)O(4) composite exhibited fine TiB(2) crystals surrounded by large densified MgAl(2)O(4) grains. This study demonstrated an energy-saving and efficient route for fabricating MgAl(2)O(4)-containing composites.