Fabrication of WSi2–Al2O3 and W5Si3–Al2O3 composites by combustion synthesis involving thermite reduction

Abstract Formation of WSi 2 –Al 2 O 3 and W 5 Si 3 –Al 2 O 3 composites was studied by thermite-based combustion synthesis. The addition of two thermite combinations composed of WO 3 +2Al and 0.6WO 3 +0.6SiO 2 +2Al into the W-Si reaction systems facilitated the combustion wave propagating in a self-sustaining manner and contributed to the in situ formation of tungsten silicides along with Al 2 O 3 . Experimental results showed that the former thermite mixture is more exothermic than the latter, and a decrease in the combustion temperature and flame-front velocity with increasing silicide phase formed in the composite. Depending on the reaction stoichiometry, the combustion wave velocity varied from 9.5 to 3.7 mm/s and temperature from 1650 to 1280 °C. A complete phase conversion and a broad range of the molar ratio of WSi 2 /Al 2 O 3 from 0.8 to 4.0 were achieved for the production of the WSi 2 –Al 2 O 3 composites. Due to the lower formation exo thermicity, the W 5 Si 3 –Al 2 O 3 composites were produced with a narrower range of W 5 Si 3 /Al 2 O 3 from 0.4 to 2.0, beyond which combustion failed to proceed. Moreover, there exist WSi 2 and unreacted W in the as-synthesized W 5 Si 3 –Al 2 O 3 composites.