(604b) Ignition of Metal Powders by Electric Spark

Energetic formulations with metal fuel additives are extensively used in propellants, explosives, pyrotechnics, and incendiaries. Currently, replacement of regular metal powders with nanocomposite metal-based materials is being considered. Such nanocomposite reactive materials are capable of very high reaction rates while maintaining the high combustion enthalpies characteristic of metals. However, such novel reactive nano-materials are often highly sensitive to impact, friction, and electrostatic discharge, making them difficult to handle. In particular, their high electrostatic discharge sensitivity (ESD) was reported. While ESD testing is common and standardized, the mechanisms of powder ignition by electric spark remain unclear. This project is aimed to establish the relationship between thermal ignition mechanism for metal powders and related nanocomposites and their ESD sensitivity. The project includes both experimental and modeling components. An explicit numerical model of the heat transfer within a powder bed subject to a pulsed electric discharge will be developed. The model will initially describe the behavior of metal powders for which the thermal ignition kinetics is well established and quantified, such as spherical magnesium. It will be further expanded for novel nanocomposite materials for which the kinetics of exothermic processes leading to ignition will be determined in separate experiments. The predictions will be validated experimentally using a standard ESD testing apparatus. This paper will present initial model formulation and experimental results.