Combustion synthesis of MoSi 2 and MoSi 2–Mo 5Si 3 composites

Abstract

An experimental study on the preparation of molybdenum disilicide (MoSi 2) and MoSi 2–Mo 5Si 3 composites was conducted by self-propagating high-temperature synthesis (SHS) from elemental powder compacts of different stoichiometries. Test specimens with six compositions including Mo:Si = 6:5, 1:1, 9:11, 3:4, 2:3, and 1:2 (corresponding to the Si content in the range of 45.5–66.7 at.%) were employed in this study. Experimental evidence shows that the propagation mode of the reaction front, combustion wave velocity, and reaction temperature are significantly influenced by starting stoichiometry and preheating temperature ( T p) of the reactant compact. In the cases of preheating at 200 and 300 °C, self-sustaining combustion featuring a spinning reaction zone was observed for the compacts of Mo:Si = 6:5, 1:1, and 9:11, and the reaction temperatures lower than the melting point of Si (1410 °C) were detected. On the other hand, a planar combustion front propagating in a steady manner was achieved in the samples with Mo:Si = 3:4, 2:3, and 1:2 at T p = 200 and 300 °C, and the reaction temperatures exceeding 1410 °C were found. However, the planar reaction font was no longer stable in the case of without preheating or at T p = 100 °C, and therefore was transformed into a localized reaction zone propagating in a spinning mode. According to the XRD analysis, formation of MoSi 2–Mo 5Si 3 composites from the reactant compacts of Mo:Si = 6:5, 1:1, 9:11, 3:4, and 2:3 was confirmed, but a significant amount of elemental Mo left unreacted was found in the cases of Mo:Si = 6:5 and 1:1. The unreacted Mo was considerably decreased by increasing the Si content in the reactant compact. For the sample of Mo:Si = 2:3, the residual Mo containing in the synthesized composite was in a small quantity. In addition, a single-phase product composed of the disilicide MoSi 2 was yielded from the sample of Mo:Si = 1:2.