Combustion Behavior of High Energy Density Borane–Aluminum Nanoparticles in Hypergolic Ionic Liquids

Incorporating high energy nanoparticulate additives is considered as a means to enhance the performance of hypergolic ionic liquid (IL) propellants. In this manuscript, we demonstrate the energy content of borane–aluminum nanoparticles produced by ball milling and examine the ignition and combustion behavior of hypergolic ILs loaded with up to 30 weight percent (wt %) of the particles, as measured by two different methods. The goal is to better understand the effects of particle loading on hypergolic ignition and combustion mechanism. Bomb calorimetry and differential scanning calorimetry/thermal gravimetric analysis (DSC/TGA) combined with X-ray diffraction (XRD) were used to determine the combustible energy content of particles with different capping layers and to examine the nature of the combustion products. Particles were found to have up to 97% of combustible metal content. Rapid scan-Fourier transform infrared spectroscopy (RS-FTIR) and photographic methods were used to examine ignition delay and the nature of the flames produced. The addition of borane–aluminum nanoparticles was found to have only small effects on ignition delay, but even small particle loadings were found to significantly change the flame structure and increase the duration of the combustion event. The effects of particle addition on specific impulse and density impulse were estimated.