Fast-Impulse Nanothermite Solid-Propellant Miniaturized Thrusters

Highly reactive nanothermites prepared by mixing bismuth trioxide or cupric oxide nanoparticles with aluminum nanoparticles were evaluated as solid propellants for small-scale propulsion applications. Miniaturized engines were fabricated from steel in three-piece configurations without a converging/diverging nozzle. Bismuth trioxide-aluminum generated 46.1 N average thrusts for 1.7 ms durations with a specific impulse of 41.4 s. Cupric oxide-aluminum generated 4.6 N thrusts for 5.1 ms durations with a specific impulse of 20.2 s. Convective and conductive reaction regimes were identified as functions of bulk packing density and confinement geometry. Average thrusts and burning durations differed by greater than an order of magnitude for equivalent nanothermites dependent on the reaction regime. Adding small amounts of nitrocellulose to the nanothermites increased specific and volumetric impulses to maximum values of 59.4 s and 2.3 mN . s/mm(3) while controllably reducing average thrusts and prolonging burning durations. The energy-conversion efficiencies of the thrusters were evaluated using a rotary-arm measurement, and a maximum efficiency of 0.19% was observed. Last, a miniaturized four-engine array was fabricated with micromachined initiators and sequentially fired. The high specific and volumetric impulses, fast combustion, and tailored reactions of nanothermites are appealing for many small-scale propulsion applications.