Metallothermic Reduction of MoO(3) on Combustion Synthesis of Molybdenum Silicides/MgAl(2)O(4) Composites

Combustion synthesis involving metallothermic reduction of MoO(3) by dual reductants, Mg and Al, to enhance the reaction exothermicity was applied for the in situ production of Mo(3)Si–, Mo(5)Si(3)− and MoSi(2)–MgAl(2)O(4) composites with a broad compositional range. Reduction of MoO(3) by Mg and Al is highly exothermic and produces MgO and Al(2)O(3) as precursors of MgAl(2)O(4). Molybdenum silicides are synthesized from the reactions of Si with both reduced and elemental Mo. Experimental evidence indicated that the reaction proceeded as self-propagating high-temperature synthesis (SHS) and the increase in silicide content weakened the exothermicity of the overall reaction, and therefore, lowered combustion front temperature and velocity. The XRD analysis indicated that Mo(3)Si–, Mo(5)Si(3)– and MoSi(2)–MgAl(2)O(4) composites were well produced with only trivial amounts of secondary silicides. Based on SEM and EDS examinations, the morphology of synthesized composites exhibited dense and connecting MgAl(2)O(4) crystals and micro-sized silicide particles, which were distributed over or embedded in the large MgAl(2)O(4) crystals.