Fast Reacting Nano Composite Energetic Materials: Synthesis and Combustion Characterization

Abstract Energetic composites are mixtures of solid fuel and oxidizer particles that when combined offer higher calorific output than monomolecular explosives. The composites traditionally deliver energy as diffusion-limited reactions, and thus their power available from reaction is much smaller than powerful explosive. Yet, technology has developed advanced particle synthesis, and nanoparticles have become more readily available. The advent of nanoparticle fuels and oxidizers enables traditionally diffusive controlled reactions to transition toward kinetically dominant reactions. This transition results in faster reacting formulations that show promise of harnessing the power equivalent to a monomolecular explosive but packaged as discretely separate fuel and oxidizer composites. This chapter will focus on developing an understanding of fundamental reaction dynamics associated with particulate media, in general. Once this foundational understanding is established, new strategies for designing aluminum fuel particles toward greater reactivity and thus faster reacting formulations will be presented. In addition to synthesis, several combustion characterization techniques will be examined to quantify combustion performance. All of this information may provide a basis for future research and applications involving aluminum-based fuels in any energetic system (i.e., as an additive to liquid propellants or even explosive formulations). Composite energetic materials with nanoscale aluminum particles play a significant role in nearly every sector of our energy-generating economy from industrial to ordnance technologies. Nanoscale aluminum fuel particles hold numerous advantages over their micron-scale counterparts. Fluoropolymers have been gaining popularity over the last decade as a favored oxidizer in these composite systems because of their unique ability to react with the passivating alumina shell present over aluminum particles. This chapter investigates the tailorability of energetic composites made of nano-aluminum (Al) combined with different fluoropolymers, by incorporating different additives into the reactive material. Diffusion-controlled reactions are limited by the proximity (i.e., diffusion distance) of reactant particles. The effect of the proximity of the oxidizer has been investigated by performing flame propagation experiments on molybdenum trioxide (MoO 3 ) combined with aluminum particles with and without surface functionalized perfluorotetradecanoic (PFTD) acid. Results showed that the surface functionalization enhanced the burn rate twice that of nonfunctionalized energetic composite. In order to control the burn velocity by altering their surface functionalizations, three different energetic composites consisting of aluminum particles with and without surface functionalization, combined with molybdenum trioxide, were used. Perfluorotetradecanoic and perfluorosebacic (PFS) acids were used to form an organic corona around the aluminum nanoparticles. Flame propagation studies revealed that energetic composites made of Al functionalized with PFTD (Al-PFTD) displayed burn velocity higher than Al/MoO 3 whereas Al with PFS/MoO 3 are almost half of Al/MoO 3 . Results showed that the fluorine content in the acids and their structural differences contribute to difference in burn velocity. The mechanisms controlling reactivity is discussed such that new approaches to particle synthesis can be developed to further advance energetic composites for the next generation.