A comparative study on combustion synthesis of Ti-Si compounds

A comparative study on the preparation of specific titanium silicides (including Ti3Si, Ti5Si3, Ti5Si4, TiSi, and TiSi2) in the Ti-Si system was experimentally conducted by self-propagating high-temperature synthesis (SHS) from elemental powder compacts of their corresponding stoichiometries. The effect of initial sample stoichiometry was investigated on combustion characteristics and product composition. Experimental evidence shows a distinct combustion front traversing the entire reactant compact in a self-sustaining manner for all of the samples adopted in this study. However, as a result of the eutectic reaction, test samples composed of Ti:Si = 3:1 and 1: 1 experienced excessive melting during the propagation of the reaction front. Moreover, the flame-front propagation rate and combustion temperature were found to vary significantly with starting stoichiometry of the powder compact. The flame-front velocity up to 50 mm/s was observed in the samples of Ti:Si = 5:4 and 5:3, in contrast to the values in the range of 2.6-3.5 mm/s for the compact of Ti:Si = 1:2. Reaction front temperatures between 1380 and 1460 degrees C were achieved by the powder compacts with Ti:Si = 5:4 and 5:3. For the samples of Ti:Si = 3:1 and 1: 1, their flame-front temperatures were comparable and about 1330 degrees C. Consistent with its slow reaction front, the Ti + 2Si sample had the lowest combustion temperature close to 1150 degrees C. The XRD analysis confirms complete conversion from the reactant with Ti:Si = 5:3 to a single-phase silicide Ti5Si3. Powder compacts of Ti:Si = 5:4 and 1: 1 yielded two silicide phases, Ti5Si4 and TiSi, in their end products. In spite of formation of a minor amount of TiSi, the disilicide TiSi2 was identified as the dominant composition in the product obtained from the Ti + 2Si sample. Combustion products containing Ti5Si3 and a large amount of unreacted Ti were synthesized from the powder compacts of Ti: Si = 3: 1, implying a poor degree of phase conversion. (c) 2006 Elsevier B.V. All rights reserved.