Thermite reduction of Ta 2O 5/SiO 2 powder mixtures for combustion synthesis of Ta-based silicides

Abstract

Tantalum silicides (including TaSi 2, Ta 5Si 3, Ta 2Si, and Ta 3Si) were prepared by solid state combustion of the Ta–Si reaction system involving thermite reduction of Ta 2O 5 and SiO 2. The thermite-based combustion is self-sustaining and contributes to the in situ formation of tantalum silicides along with Al 2O 3. The combustion front temperature and propagation velocity increased with the extent of thermite reactions for the systems adopting the thermite mixture of Al–Ta 2O 5, while both of them decreased for those using Al, Ta 2O 5, and SiO 2 as the thermite reagents. Among four silicide compounds, a better degree of phase evolution was observed for TaSi 2 and Ta 5Si 3 when compared to that of Ta 2Si and Ta 3Si. The XRD analysis indicated the presence of a small amount of Ta 5Si 3 in the TaSi 2–Al 2O 3 composite. On the formation of Ta 5Si 3 with Al 2O 3, the minor phase was Ta 2Si for the Al–Ta 2O 5-containing system. In addition to Ta 2Si, an intermediate phase TaSi 2 was detected when the Al–Ta 2O 5–SiO 2 mixture was used. However, combustion yielded comparable amounts of Ta 2Si and Ta 5Si 3 in the synthesis of the Ta 2Si–Al 2O 3 composite. Moreover, instead of forming Ta 3Si the reaction produced Ta 2Si as the dominant phase along with unreacted Ta.