SYNTHESIS, SINTERING, MICROSTRUCTURE, AND MECHANICAL-PROPERTIES OF CERAMICS MADE BY EXOTHERMIC REACTIONS

Al2O3-TiC, Al2O3-TiC0.5N0.5, Al2O3-WC, Al2O3-SiC, and Al2O3-HfB2 powders were synthesized by the aluminothermic reduction of oxides in the presence of carbon or boron. The reacted powders were milled to reduce the size of agglomerates and subsequently densified without applied pressure to near-theoretical density. Microstructures and mechanical properties of composites made from exothermically reacted powders were compared with similar ceramics made from commercially available powders. In situ sintering was possible in the Al2O3-TiC system using a closed graphite crucible to contain reaction gases. The synthesis of beta-SiC at temperatures above 1400-degrees-C via the direct reaction of the elements (SHS) was compared with SiC made by the magnesiothermic reduction of SiO2 in the presence of C after removing the MgO by leaching.