Characteristics of the initiation of chain and thermal explosions of energetic materials by pulsed laser radiation

A comparative experimental and theoretical study of the initiation of silver azide (SA) single crystals and pressed pentaerythritol tetranitrate (PETN)–metal nanoparticles by a neodymium laser pulse is performed. The main differences in the explosive decomposition of the samples are associated with the absence of the induction period and the presence of subthreshold effects in the initiation of PETN-based composites. By contrast, the initiation of SA single crystals always features an induction period, but no subthreshold effects. It is shown that the observed differences in the explosive decomposition are due to the fact that SA single crystals decompose by the chain explosion mechanism, whereas pressed PETN–metal nanoparticles samples, by the thermal explosion mechanism in the micro-hotspot mode. The kinetic parameters of the initiation of the decomposition reaction calculated within the framework of the existing model are consistent with the available experimental data. An experimental criterion for distinguishing between the chain and thermal (in micro-hotspot) mechanisms of the initiation of an explosion under the action of a laser radiation pulse is formulated, according to which the absence of the induction period and a pronounced manifestation of subthreshold effects are indicative of a thermal explosion, whereas the presence of the induction period and the absence of subthreshold effects are characteristic of a chain explosion.