Innovative Passivation Technologies for Aluminum Nanoparticles
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AbstractAluminum 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. Aluminum has an energy density (-31.05 kJ/g) nearly three times higher than most molecular high explosives and its combustion yields a highly exothermic release of energy (?'Hf (Al2O3) = -1676.8 kJ/mol).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 significant losses in the amount of reactive Al. To optimize the reactive Al content in nano-Al powders, UES has investigated the use of silicon, deposited through a modified chemical vapor deposition process, as an innovative passivation strategy for stabilizing nano-Al. Silicon has an energy density (-32.42 kJ/g) essentially equivalent to Al and also expresses high reactivity on the nano-scale. Passivation of silicon is achieved through a 34% less dense, 1-2 nm nascent oxide, additionally silicon passivation does not consume any Al, therefore, passivation of nano-Al through deposition of silicon has the potential to eliminate undesirable Sdead weight and replace it with additional reactive fuel.
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