Metallothermic Reduction of MoO₃ on Combustion Synthesis of Molybdenum Silicides/MgAl₂O₄ Composites

Combustion synthesis involving metallothermic reduction of MoO₃ by dual reductants, Mg and Al, to enhance the reaction exothermicity was applied for the in situ production of Mo₃Si-, Mo₅Si₃- and MoSi₂-MgAl₂O₄ composites with a broad compositional range. Reduction of MoO₃ by Mg and Al is highly exothermic and produces MgO and Al₂O₃ as precursors of MgAl₂O₄. 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 Mo₃Si-, Mo₅Si₃- and MoSi₂-MgAl₂O₄ 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 MgAl₂O₄ crystals and micro-sized silicide particles, which were distributed over or embedded in the large MgAl₂O₄ crystals.