Oxidation, ignition, and combustion of Al·I2 composite powders

Materials combining high energy density of metals with the biocidal activity of halogens are of interest for applications aiming to inactivate harmful aerosolized microorganisms by combined thermal and chemical effects. This effort develops nanocomposite Al-halogen materials to replace pure Al as a fuel additive in energetic formulations. Cryogenic milling of elemental aluminum and iodine is used to prepare powder-like composite materials for laboratory tests. In such materials, iodine is stabilized in aluminum matrix and is released when the materials are heated and ignited. Al·I2 composite powders with the iodine concentration from 10 to 30 wt.% were prepared. Iodine release by and oxidation of such materials were investigated using thermo-gravimetric analysis. Ignition temperatures of the prepared powders were determined at the heating rates of 1000–22,000 K/s using an electrically heated filament. Composite powders ignite at lower temperatures compared to pure Al powders. Combustion characteristics of the prepared materials were investigated using a constant volume explosion test for aerosolized powders and laser ignition test for individual particles. In both combustion experiments pure Al served as a reference. Higher combustion rate and greater total pressure were observed for the aerosolized clouds of composite powders with 15 and 20 wt.% of iodine. For individual particles, the burn times were slightly longer and flame temperatures were slightly lower compared to those of pure aluminum. Both overall iodine concentration and its stability in the composite powders affected their ignition and combustion characteristics.