Shock-induced and self-propagating high-temperature synthesis reactions in two powder mixtures: 5:3 Atomic ratio Ti/Si and 1:1 Atomic ratio Ni/Si

Abstract

The conditions for initiation and propagation of the reaction forming the intermetallic compounds Ti5Si3 and NiSi from mixtures of elemental powders of varying porosity have been investigated using shock waves of different pressure and at atmospheric pressure using hot wire ignition in air and in an argon atmosphere. In each case, the reaction either went to completion or the powder remained essentially unreacted. The conditions for the initiation of the reaction in Ti/Si are sensitive to the presence of air. Two regimes of porosity and shock pressure are found for the Ti/Si mixture which cause complete reaction. A low-energy regime with a high initial porosity (producing a low shock pressure) with 0.1 torr of residual air triggers the reaction, while no reaction is observed with a 128 pct higher shock energy and a lower initial porosity (producing a higher shock pressure) when the residual air is replaced with argon. Hot wire ignition of porous Ti/Si powder at room temperature initiates a self-propagating high-temperature synthesis (SHS) reaction more easily in air than in an argon atmosphere, while the Ni/Si powder must be heated to allow the SHS reaction to propagate in high- or low-porosity mixtures in air. These observations are compared to published work on self-sustaining reactions in multilayer films. Reasons for the difference in behavior of the two powder mixtures are discussed.