Energetic Modification of Aluminum Nanoparticles
Aluminum (Al) has an energy density (-31.05 kJ/g) nearly three times higher than most molecular high explosives and its combustion yields an exothermic release of energy (f'Hf (Al2O3) = -1676.8 kJ/mol) but is limited by surface diffusion, therefore an increase in surface area yields a direct increase on reaction rate. Aluminum nanopowders (nano-Al) possess surface areas on the order of 20-40 m2/g and have attracted interest throughout the energetics community for propellant and metallization applications. Unpassivated nano-Al powders are highly pyrophoric and require stabilization through formation of a nascent oxide layer (2-6 nm), however, this process accounts for a 14-38% loss of reactive aluminum. To improve reaction kinetics for nano-Al based energetic formulations, UES proposes use of thin (2-5 nm) fluoropolymer coatings deposited on the oxide surface of nano-Al either through wet-chemical deposition techniques or through use of plasma polymerization. Fluoropolymers are known to be highly effective oxidizers for aluminum and should initiate and accelerate reaction between nano-Al and additional oxidizers. Additionally, fluoropolymer coatings will also serve as a gasifying agent to increase reaction pressures in nano-Al based energetic formulations and due to their naturally hydrophobic nature should improve the stability of nano-Al by inhibiting premature oxidation due to humidity.
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