Field-activated combustion synthesis of Ta–Si intermetallic compounds

Abstract

The synthesis of silicides of tantalum (TaSi2, Ta5Si3, Ta2Si, and Ta3Si) by field-activated combustion synthesis was investigated. The phases TaSi2, Ta5Si3, and Ta2Si can be synthesized in relatively pure form through field activation. The first compound requires a threshold field of 6 V cm−1 to initiate a combustion wave. The second and third compounds can be synthesized with all field values (0 < E < 20 V cm−1), but require considerable ignition time when E = 0. The stoichiometry Ta3Si does not sustain a combusion front unless E ≥ 20 V cm−1. However, the product is not the desired single phase. Wave velocities in the synthesis of the Si-rich phase, TaSi2, are considerably lower than those of the other two and showed a much weaker dependence on the field. The mechanism of phase formation for TaSi2 and Ta5Si3 was investigated from frozen wave analysis. No intermediate phase forms in the TaSi2 case, while in the case of Ta5Si3, TaSi2 is present as an intermediate phase. Additional investigations on the mechanism of silicide formation included isothermal solid–solid diffusion-couple and solid–liquid experiments.