Innovative Passivation Technologies for 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 ("'Hf (Al2O3) = -1676.8 kJ/mol) but is limited by surface diffusion, therefore an increase in surface area yields a direct increase on the 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 optimize the reactive Al content in nano-Al powders, UES proposes 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, although passivation of silicon is achieved through a 34% less dense, 1-2 nm nascent oxide, or the use of organic coatings. Therefore, passivation of nano-Al through deposition of silicon has the potential to eliminate undesirable Sdead weight and replace it with additional reactive fuel.