Mechanism of microwave-initiated ignition of sensitized energetic nanocomposites

One of the challenges in propellant formulation is the inability to moderate the burn rate dynamically. Here, we consider spatially localized remote ignition of additively manufactured composites via microwave absorption. Previous studies demonstrated that a passivating shell on Ti nanoparticles (nTi) enhances microwave absorption. Incorporated within a polyvinylidene fluoride (PVDF) matrix, Ti/PVDF films ignite under microwave irradiation in air. To gain more comprehensive insight into pre-ignition behavior, the ignition delay was studied as a function of applied power and the microwave susceptor loading. Infrared (IR) camera studies were further used to investigate the heating behavior of the films under variable power. We found that ignition delay decreases with increasing power to an apparent heating saturation region, where the ignition sensitivity is limited by the combustion reaction kinetics. Thermogravimetric analysis coupled with differential scanning calorimetry (TGADSC) showed that nTi oxidizes with O2 at lower temperatures than fluorination with PVDF and drives combustion. Findings in this work build a pathway for remote and controlled ignition of solid propellants via microwave radiation.