Impact ignition of nano and micron composite energetic materials

Abstract

Nanoscale reactive materials demonstrate three orders of magnitude reduced laser ignition sensitivity compared to their micron scale counterparts. Reduced ignition delay times have been reported for a variety of nano composites including aluminum combined with another metal (e.g., Ni), metallic oxides (e.g., MoO 3, Fe 2O 3, CuO, WO 3), or polymer binders such as polytetrafloroethylene (Teflon™). A new reported melt dispersion mechanism associated with nano-aluminum particle ignition explains the enhanced thermal ignition sensitivity associated with nano-aluminum composites. As a comparison to laser thermal ignition behaviors, this study focuses on impact induced ignition of nano- and micron-aluminum particle composites that also include Ni, MoO 3, or Teflon. A modified type-12 impact tester is used to measure ignition of the energetic composites to drop weight impact. Ignition is determined using high-speed thermal imaging. To assess the influence of the alumina passivation shell on the ignition dynamics, oxide-free nano-aluminum passivated with a perfluoroalkyl carboxylate self-assembled monolayer has also been investigated. Results show that the difference in ignition sensitivity between nano and micron composites is significantly greater with laser than with mechanical ignition and the melt dispersion mechanism does not describe impact ignition.