Benchtop energetics progress

Abstract

We have constructed an apparatus for investigating the reactive chemical dynamics of mgscale energetic materials samples. We seek to advance the understanding of the reaction kinetics of energetic materials, and of the chemical influences on energetic materials sensitivity. We employ direct laser irradiation, and indirect laser-driven shock, techniques to initiate thin-film explosive samples contained in a high-vacuum chamber. Expansion of the reacting flow into vacuum quenches the chemistry and preserves reaction intermediates for interrogation via time-of-flight mass spectrometry (TOFMS). By rastering the sample coupon through the fixed laser beam focus, we generate hundreds of repetitive energetic events in a few minutes. A detonation wave passing through an organic explosive, such as pentaerythritol tetranitrate (PETN, C 5H 8N 4O 12), is remarkably efficient in converting the solid explosive into final thermodynamically-stable gaseous products (e.g. N 2, CO, CO 2, H 2O⋯). Termination of a detonation at an explosive-to-vacuum interface produces an expanding pulse of hyperthermal molecular species, with leading-edge velocities ∼ 10 km/s. In contrast, deflagration (subsonic combustion) of PETN in vacuum produces mostly reaction intermediates, such as NO and NO 2, with much slower molecular velocities; consistent with expansion-quenched thermal decomposition of PETN. We propose to exploit these differences in product chemical identities and molecular species velocities to provide a chemically-based diagnostic for distinguishing between "detonation- like" and deflagration events. We report recent progress towards the quantitative detection of hyperthermal neutral species produced by direct laser ablation of aluminum metal and of organic energetic materials, as a step towards demonstrating the ability to discriminate slow reaction intermediates from fast thermodynamically-stable final products. © 2012 American Institute of Physics.