Al/SnO₂ Nanothermite ESD Desensitization by Means of the Elaboration of Tailored SnO₂–Polypyrrole Composites

Abstract

Incidents can occur when handling energetic materials (EMs) due to their sensitivity to external stimuli. Mechanical (friction, impact) and electrical (electrostatic discharge (ESD)) stimuli can trigger involuntary ignition of EMs. Nanothermites, defined as highly reactive mixtures of a metal and a metal oxide, show interesting reactive properties (high temperature/amount of heat). However, their extreme sensitivity to ESD is a significant drawback in their development. With a sensitivity threshold of lower than a millijoule and considering the human body capacity discharge is a few tens of millijoules, the handling of such energetic mixtures is extremely hazardous. ESD desensitization is therefore of crucial importance for the use of these materials. To achieve this goal, polypyrrole (PPy) conductive polymer was used as an additive within an Al/SnO 2 energetic formulation. This polymer is able to easily conduct the electrostatic charges, which is useful to avoid an ignition after a spark stimulus. PPy was added to the nanothermite through the elaboration of SnO 2 −PPy composites. Delaying the SnO 2 introduction time during pyrrole's polymerization (t = 0, 1, 24 h) changed the microstructures of the composites. The various SnO 2 −PPy composites highlighted that the additive's distribution within the composite is a key component for the modulation of ESD sensitivity. For example, this threshold is higher for a nanothermite formulated with the composite elaborated at t = 0 h (96.5 mJ with 7.5 vol % of polymer) than a composition based on the composite at t = 24 h (16.9 mJ with 8.2 vol % of polymer). Meanwhile, the reactive properties are decreased. The loss of reactivity (e.g. combustion speed) was explained by the thermal insulating property of the additive. Overall, the aim of this study is to help in the understanding of ESD desensitization of nanothermites in order to make them safer for operators and adapted to the required applications.