Chemical Engineering Journal, Vol.293, 112-117, 2016
Ignition and combustion of boron-based Al center dot B center dot I-2 and Mg center dot B center dot I-2 composites
Stable ternary powders of Al center dot B center dot I-2 and Mg center dot B center dot I-2 composites of interest for agent defeat applications were prepared by mechanical milling. All powders contained 20 wt.% of iodine. Powder ignition was characterized using a heated filament experiment. Ignition kinetics was compared to the kinetics of events occurring upon slow heating of these materials in thermo-analytical experiments. Individual particle combustion was studied by seeding the powder into a premixed hydrocarbon-air flame. Both, particle burn times and temperatures were measured optically. Aerosol combustion of the powders was tested in a constant volume explosion chamber. Ignition temperatures for the Mg center dot B center dot I-2 composites were lower than those for the Al center dot B center dot I-2 composites. Iodine release occurring due to the formation of AlB2 and MgB2 was a likely ignition trigger for Al center dot B center dot I-2 and Mg center dot B center dot I-2 composites, respectively. The burn times of these composites were longer than those for pure Al and Mg powders. Burn times for Mg center dot B center dot I-2 particles were shorter than for the same size particles of Al center dot B center dot I-2. Combustion temperatures of the composite powders were lower than those of pure Al and Mg. In aerosol combustion, the rate of pressurization and maximum pressure were inversely proportional to the concentration of boron. The combustion efficiency was expressed through a ratio of the experimental maximum pressure to that predicted by a thermodynamic equilibrium calculation. This efficiency was the same for Al and Al center dot B center dot I-2 composites. The efficiency for Mg center dot B center dot I-2 composites exceeded that of pure Mg. (C) 2016 Elsevier B.V. All rights reserved.