Evaluating compositional effects on the laser-induced combustion and shock velocities of Al/Zr-based composite fuels

Abstract

Laser-induced air shock from energetic materials (LASEM) is a laboratory-scale method for assessing the microsecond and millisecond timescale performance of conventional military explosives. The technique has been combined with optical emission detection schemes to evaluate energy release during detonation and post-detonation timescales from the combustion of metal powders and mixtures of metal powders and explosives. Recently, Al/Zr reactive composite powders have been synthesized via high energy ball milling with the aim of decreasing ignition thresholds while simultaneously increasing overall combustion efficiency and burn time. Here, we utilize LASEM to evaluate micron-sized 3Al:2Zr, Al:Zr, and Al:3Zr fuel powders and compare their behavior to micron-sized Al powder, a commonly used explosive additive. We observed a rapid ignition of Al/Zr powders instead of the delayed ignition of the secondary deflagration cloud that is observed for pure Al. The composites also demonstrated longer burn times compared to Al particles of similar size. We also observed enhanced laser-induced shock velocities for the composite samples, implying increased energy release in the microsecond time regime compared to Al. In addition, we present LASEM data using Al/Zr mixed with trinitrotoluene (TNT), and associated CHEETAH calculations. As expected, adding pure Al to TNT lowers the laser-induced shock velocity, and we observe a further decrease of this velocity when using composite additives. The complex interplay of the metals with each other and the TNT reaction products is yet to be fully understood.