Electro-Static Discharge (ESD) Sensitivity of Reactive Powders and its Mitigation

Abstract : This work followed our previous study characterizing ignition of pure metal powders by electrostatic discharge. Here, the experiments are extended to reactive nanocomposite materials, including several thermite compositions prepared by different methods. All experiments used a high voltage spark to ignite materials; optical emission and pressure generated by combustion were monitored in real time. Experiments showed that ignition event for all materials can be described using two stages. First, a fraction of the powder struck by the spark is ignited directly and lifted from the sample holder by a weak shockwave generated by the discharge. This prompt ignition occurs within hundreds of microseconds. The promptly ignited particles are lifted along with particles that are not ignited. Flame propagation through a cloud of lifted particles occurs on the time scale of 1 - 10 ms and is registered as the second, delayed ignition stage. The structure of the reactive material affects critically the ignition and ensuing combustion rates. For fully-dense powders prepared by arrested reactive milling, heterogeneous reactions between components are important in all stages of combustion. Such materials perform best in oxygen depleted environments. For mixed nanopowders, reaction with surrounding oxidizer is important.