(458k) Microwave Controlled Ignition and Combustion of an AP Composite Solid Propellant Using Graphene Oxide-Wrapped Nanoscale Thermites

This effort reports on the development of AP composite propellants that, in small scale, high thermal loss environments, have ignition, combustion, and extinguishment that can be controlled by application of microwave irradiation. In order to localize microwave ignition at the burning surface of the propellant, we incorporate into the propellants recently developed graphene oxide (GO)-wrapped nanoscale Al/Fe2O3 thermites, whose GO coatings, upon heating, undergo reduction to form reduced graphene oxide (rGO) coated thermites. In this effort we cast small ~1 mm diameter wires of propellant supported on quartz and PTFE substrates that are ignited within a 2.46 GHz resonant microwave cavity with a microwave power of ~300 to 1000 W. Microwave ignition is achieved on one end of the wire by first igniting and quenching the propellant strand to convert GO near the burning surface to rGO. Modulation of the microwave field demonstrates that ignition with delays of ~0.4 s are possible, and upon removal of the microwave field, the burning front is extinguished due to the high thermal loss of the propellant size and configuration. We demonstrate the ability to successfully ignite, extinguish, and reignite propellant many times in succession. We explore the effects of microwave power (field strength) on ignition delay and burning rate, report the effects of GO and rGO on the dielectric properties of the propellant, and investigate the composition of quenched burning surfaces in order to understand mechanisms responsible for the microwave reignition capability.