Iodine release, oxidation, and ignition of mechanically alloyed Al-I composites

Multifunctional materials combining the high energy density of metal fuels with the ability to generate biocidal combustion products are of interest for defeat of stockpiles of biological weapons. In this study, new Al-I composites are prepared and investigated, which are expected to combust similarly to Al powder while releasing biocidal iodine-containing reaction products. Materials are prepared by mechanical milling of pure Al powder and iodine at cryogenic temperatures. Prepared materials are stable at room temperature and contain more than 10 wt % of iodine. Two samples with the same nominal compositions were prepared using different milling conditions. Thermogravimetric measurements at different heating rates were used to characterize reactions of iodine release and oxidation of the prepared materials. Oxidation was studied with O ₂ serving as an oxidizer. Ignition of the prepared materials was studied by coating them onto an electrically heated filament and using optical diagnostics to identify ignition temperatures at different heating rates. It was observed that iodine is released from the prepared materials in several steps. At low temperatures, iodine release is similar to volatilization of elemental iodine and AlI₃. Substantial amounts of iodine are retained to higher temperatures and begin to volatilize when the sample temperature approaches the Al melting point. Oxidation of the prepared materials in O₂ begins at lower temperatures than that for pure Al. Melting of Al accelerates both oxidation and iodine release rates. Prepared materials ignite at substantially lower temperatures than pure Al, and a correlation between ignition and iodine release is identified.