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The heterogeneous interaction between nitromethane (NM), particles of nanoscale aluminum (38 and 80 nm diameter), and fumed silica is examined in terms of the deflagration and detonation characteristics. Burning rates are quantified as functions of pressure using an optical pressure vessel up to 14.2 MPa, while detonation structure is characterized in terms of failure diameter. Nitromethane is gelled using fumed silica (CAB-OSIL), as well as by the nanoaluminum particles themselves. Use of nanoaluminum particles with fumed silica slightly increases burning rates compared to the use of larger diameter Al particles; however distinct increases in burning rates are found when CABO-SIL is removed and replaced with more energetic aluminum nanoparticles, whose high surface area allows them to also act as the gellant. Mixtures including fumed silica yield a reduced burning rate pressure exponent compared to neat NM, while mixtures of aluminum particles alone show a significant increase. Failure diameters of mixture detonations are found to vary significantly as a function of 38 nm aluminum particle loading, reducing more than 50% from that of neat nitromethane with 12.5% (by mass) aluminum loading. Failure diameter results indicate a relative minimum with respect to particle separation (% loading) which is not observed in other heterogeneous mixtures., Approved for public release; federal purpose rights., The original document contains color images. Published in Propellants Explos. Pyrotech., v34 p385-393, 2009.

An experimental investigation on the combustion behavior and conversion efficiency of nanoaluminum and liquid water mixtures was conducted. Burning rates and chemical efficiency of aluminum-water and aluminum-water-poly(acrylamide-co-acrylic acid) mixtures were quantified as a function of pressure (from 0.12 to 15 MPa), nominal aluminum particle size (for diameters of 38, 50, 80, and 130 nm), and overall equivalence ratios (0.67phi1.0) under well-controlled conditions. Chemical efficiencies were found to range from 27 to 99% depending upon particle size and sample preparation. Burning rates increased significantly with decreased particle size attaining rates as high as 8 cm/s for the 38 nm diameter particles above approximately 4 MPa. Burning rate pressure exponents of 0.47, 0.27, and 0.31 were determined for the 38, 80, and 130 nm diameter particle mixtures, respectively. Also, mixture packing density varied with particle size due to interstitial spacing, and was determined to affect the burning rates at high pressure due to inert gas dilution. The presence of approximately 3% (by mass) poly(acrylamide-co-acrylic acid) gelling agent to the nAl/H2O mixtures had a small, and for many conditions, negligible effect on the combustion behavior., Published in Combustion Science and Technology, v180 n12 p2127-2142, Dec 2008. Sponsored in part by ONR. Prepared in collaboration with Los Alamos National Laboratory, Los Alamos, NM and Purdue University, West Lafayette, IN.