Assembly and encapsulation of aluminum NP's within AP/NC matrix and their reactive properties

Aluminum nanoparticles (Al NPs) are commonly employed as fuel supplement to increase the energy density of propellants. However, due to the highly agglomerated state of the NPs and significant pre-combustion sintering, ignition and combustion are not as facile as they could be. In this work, we employed a spray approach to generate near monodisperse microparticles of Al NP's encapsulated within ammonium perchlorate (AP) and a binder (nitrocellulose (NC)) The results show that Al/AP/NC composites have an ignition temperature (∼700 K), which is significantly lower than Al melting point (∼933 K). The reactivity of Al/AP/NC composites was also tested in a confined cell where we find that although the peak pressure for Al/AP/NC is comparable to that of physically mixed Al/CuO nanothermite, the impulse generated is more than two times higher. The measured flame temperature of Al/AP/NC composites were as high as 2800 K, which is ∼500 K higher than Al/AP composites without NC. Furthermore, the potential mechanism for the early ignition of these composites were investigated. It is proposed that gaseous acid released from AP could play an important role in weakening the protective oxide shell on Al nanoparticles which could subsequently lead to the reaction of Al in the high-pressure oxygenated environment at lower temperature.