Thermite reduction of Ta2O5/SiO2 powder mixtures for combustion synthesis of Ta-based silicides

Tantalum silicides (including TaSi2, Ta5Si3, Ta2Si, and Ta3Si) were prepared by solid state combustion of the Ta–Si reaction system involving thermite reduction of Ta2O5 and SiO2. The thermite-based combustion is self-sustaining and contributes to the in situ formation of tantalum silicides along with Al2O3. The combustion front temperature and propagation velocity increased with the extent of thermite reactions for the systems adopting the thermite mixture of Al–Ta2O5, while both of them decreased for those using Al, Ta2O5, and SiO2 as the thermite reagents. Among four silicide compounds, a better degree of phase evolution was observed for TaSi2 and Ta5Si3 when compared to that of Ta2Si and Ta3Si. The XRD analysis indicated the presence of a small amount of Ta5Si3 in the TaSi2–Al2O3 composite. On the formation of Ta5Si3 with Al2O3, the minor phase was Ta2Si for the Al–Ta2O5-containing system. In addition to Ta2Si, an intermediate phase TaSi2 was detected when the Al–Ta2O5–SiO2 mixture was used. However, combustion yielded comparable amounts of Ta2Si and Ta5Si3 in the synthesis of the Ta2Si–Al2O3 composite. Moreover, instead of forming Ta3Si the reaction produced Ta2Si as the dominant phase along with unreacted Ta.

► Solid state combustion involving thermite reduction of Ta2O5 and SiO2 was firstly performed for the formation of tantalum silicides, including TaSi2, Ta5Si3, Ta2Si, and Ta3Si.
► Two thermite mixtures, Al–Ta2O5 and Al–Ta2O5–SiO2, were adopted and their influence on the combustion characteristics and phase constituents of the final products was studied.
► A high degree of phase evolution forming Al2O3-added TaSi2 and Ta5Si3 was achieved by adopting the thermite mixture of Al–Ta2O5 in the Ta–Si combustion system.
► Variations of the combustion temperature and flame-front velocity with sample stoichiometry were presented.