Ignition sensitivity of composite energetic materials to electrostatic discharge

The Safe handling of powdered composite energetic materials requires an understanding of their response to electrostatic ignition stimuli. It is important to focus on and minimize characteristics of the reaction that promote sensitivity to ESD while still maintaining high performance in combustion. This body of work investigates the ignition response of energetic materials to ESD by examining various parameters including packing density, electrical conductivity, and ignition delay. Inter-particle connectivity plays a major role in the ignition sensitivity of composite energetic materials when using electric ignition. Results show that the ignition delay times are dependent on the powder bulk density with an optimum bulk density of 50%. The packing fractions for particle geometries and electrical conductivity were analyzed and assist in explaining the ignition behavior as a function of bulk density. The Al+PTFE composition has a low electrical conductivity and is not ignition sensitive to EDS. Small concentrations of carbon nanotubes (CNTs) and graphene nanoplatelets (GNPs) were added to Al+PTFE, which significantly increased the electrical conductivity to approximately 100 S/cm with only 4 vol. % of GNPs and 1 vol. % of CNTs. ESD ignition was achieved only for a discrete range of conductivity corresponding to approximately 2x10-3 S/cm. The ESD ignition sensitivity of nano-scale Al particles, synthesized with varying shell thicknesses ranging between 2.7 and 8.3 nm, and MoO3 was observed in terms of ignition delay times. It was discovered that the ignition delay increased as the alumina shell thickness increased. These results correlate with the resistivity of the sample which also increases as the alumina content increases. A model was developed using COMSOL Multiphysics for a single Al particle and its initiation through joule heating. The ignition delay in the model was consistent with the experimental results suggesting that joule heating is a major contributor to the ESD ignition mechanism.