Underwater self-sustaining combustion and micro-propulsion properties of Al@FAS-17/PTFE-based direct-writing nanothermite

Micro-propulsion underwater technology has been an extensively concerned topic in advanced marine energy systems because of its wide prospects in high-precision prospecting and positioning. Wherein, the design and selection of propellant in energy-supply systems are the key issues to greatly explore its future application. Here, the hydrophobic thermite sticks which contain hydrophobic polytetrafluoroethylene nanoparticles and modified aluminum coated with 1H, 1H, 2H, 2H-perfluorodecyltriethoxysilane shells, were fabricated via a simple direct-writing approach. The modified thermite sticks exhibit stable underwater combustion and self-sustained propagation with a small diameter size (0.94 ± 0.05 mm). In-situ observation shows that the underwater reaction process could be divided into three steps: laser-induction, organic decomposition-dissolution, and thermite reaction. The aging results indicate that the thermite sticks demonstrate an excellent storage stability wherever in air or underwater environments. Simultaneously, it is found that its critical energy required to sustain stable underwater combustion is higher than that in air. Most notably, it not only can be used as the fuels for controllable miniature underwater propulsion, but also can be applied as the energy-delivery materials to expand thrust capacity of vehicles by igniting higher impulse explosives, such as CL-20.