Ani Abraham

Preparation, Ignition, and Combustion of Mg·S Reactive Nanocomposites

ABSTRACT Elemental magnesium and sulfur powders were ball milled to prepare a nanocomposite material, Mg·S. Ignition of the prepared powder was characterized using both a heated filament experiment and electric spark. Combustion of individual particles was studied by injecting the powder into a premixed hydrocarbon-air flame. Combustion of powder clouds was examined using a constant volume explosion chamber. Biocidal effect of the produced combustion products against aerosolized endospores of Bacillus thuringiensis (simulant of Bacillus anthracis) was quantified. The powders ignited at lower temperatures, compared to pure magnesium. Delayed ignition was observed for powders initiated by spark and for powder clouds ignited in a constant volume chamber by a heated wire. The delay is likely due to the formation of an evaporated sulfur cloud preceding ignition. The composite material burned faster than pure magnesium, which was shown by shorter measured burn times for individual particles, and by higher rates of pressure rise in the constant volume explosion experiments. The optical emission spectra produced by burning Mg·S nanocomposite powders exhibited an unusually strong emission at short wavelengths; additional spectroscopic studies of such flames are of interest. Combustion products generated by Mg·S composite powders effectively inactivated aerosolized spores; the effectiveness of inactivation was comparable to some previously examined formulations, including aluminum-based composite powders containing iodine.

Aluminum-based materials for inactivation of aerosolized spores of Bacillus anthracis surrogates

ABSTRACT Energetic materials generating biocidal combustion products to disable airborne pathogenic microorganisms (including bio-threat agents) were designed as compounds of halogens and metals with high heats of oxidation. Thermally stable Al-based powders containing iodine and chlorine were prepared using ball-milling at room and cryogenic temperatures. Such powders can replace pure aluminum in metallized energetic formulations. Their stability and halogen release were quantified using thermo-gravimetric analysis. Ignition temperatures were determined by coating prepared powders onto an electrically heated filament. All prepared composites had lower ignition temperatures and longer combustion times compared to pure Al. In separate experiments, combustion products generated by injecting the prepared powders into an air-acetylene flame were mixed with a well-characterized bioaerosol. Inactivation of viable bioaerosol particles exposed to the heated combustion products for a short period of time (estimated to be 0.33 s) was quantified. The combustion products of materials investigated in this study effectively inactivated the aerosolized spores of two tested surrogates of Bacillus anthracis (B. atrophaeus and B. thuringiensis var kurstaki). A ternary composite with 20 wt% of iodine, 40 wt% of aluminum and 40 wt% of boron was found to be most attractive based on both its stability and efficiency in inactivating the aerosolized spores. The inactivation achieved was primarily attributed to chemical stresses as the thermal effect could not solely produce the high measured levels of inactivation. The findings point to a possible synergy of the thermal and chemical spore inactivation mechanisms.