(688a) Aluminum Agglomeration Reduction in Composite Propellants Using Nanostructured Al/Hydrocarbon Particles

In recent years there has been significant interest in using nanoscale aluminum to alleviate product agglomeration in composite solid propellants. However, nAl still produces agglomerates several orders of magnitude larger than the nanoparticles and can result in unsatisfactory propellant strength, mixture viscosity, and poor aging characteristics. To alleviate some of these issues, micron sized aluminum (Al)/poly(tetrafluoroethylene) (PTFE) composite particles produced via high intensity milling have recently been considered. These particles consist of low levels of PTFE inclusion (10-30 wt.%), which result in altered ignition and agglomeration behavior when used in a composite propellant. However, their use can result in more toxic propellant combustion products (HF) and production of particles must be done carefully to prevent hazardous milling induced reactions.

Hydrocarbon inclusion in aluminum has also been shown to alter aluminum ignition behavior but has yet to be investigated in propellants. Unlike PTFE, the inclusion of hydrocarbons (e.g. low density polyethylene, LDPE) into aluminum through high intensity milling is safer as the mixture is less susceptible to milling induced reactions.  Additionally, composite Al/hydrocarbon particles should not increase the toxicity of propellant combustion products.

In this work, 10 wt.% LDPE inclusion modified aluminum particles are used in a composite solid propellant to enhance aluminum combustion and reduce agglomeration. To this end, the effect of particle production method (cryomilled vs. high intensity milled) and resulting differences in particle shape, size, and morphology on propellant characteristics (density and viscosity), theoretical propellant performance, burning rate, metal particle ignition, agglomeration, and metal combustion efficiency are addressed.