An experimental investigation on combustion synthesis of transition metal silicides V5Si3, Nb5Si3, and Ta5Si3

Preparation of transition metal siticides V5Si3, Nb5Si3, and Ta5Si3 was conducted by self-propagating high-temperature synthesis (SHS) from elemental powder compacts at their stoichiometries. The propagation mode of self-sustaining reactions, flame-front velocity, combustion temperature, and phase composition of end products were extensively studied. For the reactant compacts from the mixtures of V:Si = 5:3 and Ta:Si = 5:3, a planar flame front propagating in a steady manner was observed, with or without sample preheating. On the other hand, a preheating temperature of 200 degrees C or above was required by the Nb-Si powder compact to initiate the self-sustaining combustion. Moreover, it was found that the planar reaction font was not stable in the samples of Nb:Si = 5:3 and was transformed into a localized reaction zone propagating in a spinning mode. For all three types of the samples, as the sample density and preheating temperature increased, the combustion temperature was found to increase and the flame-front velocity was correspondingly enhanced. According to the XRD analysis, formation of single-phase silicides V5Si3 and Nb5Si3 from the reactant compacts of 5V + 3Si and 5Nb + 3Si, respectively, was confirmed. The samples of 5Ta + 3Si yielded predominantly the silicide Ta5Si3, along with an intermediate phase Ta,Si in a small amount. Based upon the temperature dependence of combustion wave velocity, the activation energies associated with combustion synthesis of V5Si3, Nb5Si3, and Ta5Si3 were determined to be 111.5, 259.2, and 105.2 kJ/mol, respectively. (c) 2006 Elsevier B.V. All rights reserved.