Ignition and combustion of boron-based Al·B·I₂ and Mg·B·I₂ composites

Stable ternary powders of Al·B·I₂ and Mg·B·I₂ 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·B·I₂ composites were lower than those for the Al·B·I₂ composites. Iodine release occurring due to the formation of AlB₂ and MgB₂ was a likely ignition trigger for Al·B·I₂ and Mg·B·I₂ composites, respectively. The burn times of these composites were longer than those for pure Al and Mg powders. Burn times for Mg·B·I₂ particles were shorter than for the same size particles of Al·B·I₂. 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·B·I₂ composites. The efficiency for Mg·B·I₂ composites exceeded that of pure Mg.