Nanoenergetics and High Hydrogen Content Materials for Space Propulsion

Progress in the past year has occurred in the following areas: 1) understanding the role of pH and rheology on Al/water combustion, 2) encapsulation of nanoparticles in crystals for propellants, 3) disrupting ignition of aluminum with fluorocarbon inclusions, 4) the combustion of micron aluminum with hydrogen peroxide, and high speed PLIF applied to composite propellants, 5) the thermochemical behavior of Ni-coated Al particles, 6) the effects of particle size on melting, diffusion, and reactions, 7) the pyrophoricity of nano-aluminum particles, 8) the thermal decomposition and high temperature oxidation of ammonia borane (NH3BH3), particularly as an energetic fuel/additive, and 9) investigations of solid oxidizer and gaseous fuel combustion performance using counterflow burners and reverse hybrid motors. Each of these topics are described in more detail below. The Dependence of Nano-Aluminum and Water Propellant Combustion on pH and Rheology Over the past few years, the combustion of nano-aluminum/water (nAl/H2O) propellants has been widely reported, but further progress has been slowed for the following reason: the loosely correlated trends in combustion data are insufficient in guiding further research efforts, and they cannot be used to significantly improve the Isp observed in static rocket motor tests. It was previously found that different mixing techniques (hand, planetary and resonant mixers, duration and temperature), or equivalence ratio gave rise to different burning rates, but the influence of pH and rheology on nAl/H2O propellants was not considered. We find that the effects of pH on nAl/H2O propellants are profound, and correlate well with viscosity, lowpressure deflagration limits, burning rate exponents, and rocket motor performance. Our findings suggest that coagulation can influence the pressure exponent over a wide range of values (0.340.68). For particle diameters < 1 μm, dispersion during mixing is affected more by electrostatic repulsion from charged ions than from mechanical agitation, and this is reflected through zeta potential and viscosity measurements at different pH levels. Additionally, we observe that pH has an influence on nAl/H2O reaction kinetics during ignition, as the propellant transitions from low temperature oxidation to high temperature combustion. Preparation and Characterization of Energetic Crystals with Nanoparticle Inclusions In this work, we have reported on the preparation and characterization of energetic crystals with nanoparticle inclusions. We focus on the nanosized iron (III) oxide-ammonium perchlorate system, generated using an ethyl acetate-acetone antisolvent:solvent system. It was shown that capture is dependent on antisolvent-to-solvent ratio; increased quantities of antisolvent lead to faster growth rates, smaller crystals, and improved capture. Additionally, the Report Documentation Page Form Approved