Ignition phenomena in combustion synthesis: An experimental methodology

An experimental methodology is presented to investigate the ignition in combustion synthesis. The aim of this work is to study the ignition phenomena, separating the initiation from the propagation process. The reactions were activated by a CO2 laser with a power range from 20 to 60 W. The experimental configuration was set to avoid the sample heat losses. All the experiments were performed in thermal explosion mode. The studied system was Ni-Al at three compositions (Ni:Al=3:1, Ni:Al=1:1 and Ni:Al=1:3). The results indicate that the ignition temperature is not affected by the laser power applied, but it is characteristic for each composition. A theoretical approach, aimed to the ignition energy calculation, supports the experiments. The calculated ignition energy, for the investigated powder mixtures, is equal to 17+/-0.5 kJ/mol(at), independent of stoichiometric ratio and of used heating ramps. A mechanistic interpretation of the ignition is attempted to compare experimental results and numerical simulations. (C) 2002 American Institute of Physics.