Organically-Capped, Nanoscale Alkali Metal Hydride and Aluminum Particles as Solid Propellant Additives

Abstract

This Paper reports on organometallic composites, containing nanoscale aluminum and lithium-based hydride fuel particles, as solid propellant additives. Theoretical performance is evaluated for bimodal metal propellant formulations containing capped fuel additives (nanoMetallix LLC) and aluminum. Replacing aluminum with nanoMetallix capped fuel additives reduces specific impulse, adiabatic flame temperature, condensed-phase products, and hydrochloric acid. Combustion behavior is investigated using high-speed video techniques, including flame emission, laser backlit configurations, and a two-camera ratiometric bandpass emission technique used to detect lithium. Agglomeration behavior of the nanoMetallix particles at atmospheric pressure is similar to nanoaluminum (nAl), producing large aggregates that ignite quickly, increasing radiative heat feedback. Spectrally filtered video identifies lithium vapor around the nanoMetallix particles on and above the burning surface, suggesting lithium vapor is released close to the surface. Pressurized burning rate measurements indicate nanoMetallix-based propellant burning rates are up to approximately 14% higher than similar nAl-based propellants at and below 6.89 MPa. Above this pressure, nanoMetallix propellants exhibit plateau pressure dependence, likely an effect of the different capping agents used. This Paper shows organically-capped nanoscale particles are a promising alternative to nano/microaluminum in composite solid propellant formulations.