Effects of oxide precursors on fabrication of Mo5Si3-Al2O3 composites via thermite-based combustion synthesis

Fabrication of the Mo5Si3-Al2O3 composite with a broad composition range was studied by thermite-based combustion synthesis. The addition of two thermite mixtures composed of 0.6MoO3 + 0.6SiO2 + 2Al and MoO3 + 2Al into the Mo-Si reaction system was thermally beneficial for the self-sustaining combustion process. The former thermite reagent is less exothermic than the latter. Moreover, experimental results showed that the combustion temperature and flame-front velocity decreased with increasing molar ratio of Mo5Si3 to Al2O3 formed in the composite. As a consequence, the MoO3/SiO2/Al-based reaction scheme was adopted to synthesize composites with Mo5Si3/Al2O3 from 0.4 to 0.7, and MoO3/Al-based system was for the products with Mo5Si3/Al2O3 from 0.8 to 1.6. The XRD pattern indicated Mo5Si3 as the dominant silicide. Mo3Si was formed as the minor phase, because a small amount of Si dissolved in Al2O3. This was confirmed by the presence of both Al2O3 and aluminum silicate, a solid solution of Al2O3 and SiO2, in the final products.