Reactive, mechanically alloyed Al · Mg powders with customized particle sizes and compositions

Previous work showed that particles of mechanically alloyed Al · Mg powders burn faster than aluminum. However, such powders were coarser than fine aluminum commonly used in energetic formulations. This work addresses preparation of mechanically alloyed Al · Mg powders in which both internal structures and particle size distributions are adjusted. Powders with 50-90 at.% Al were prepared and characterized. Milling protocol was optimized to prepare equiaxial, micron-scale particles. Ignition temperatures measured using an electrically heated filament were much lower than those of pure Al powders and are close to those of Mg. Powders were aerosolized and ignited in air; the maximum pressure was higher, rates of pressure rise were greater, and ignition delays were shorter for the mechanically alloyed powders than for pure Al with directly comparable particle size distributions. Individual particle combustion experiments used laser ignition and showed that the alloyed particles burn in two stages, with the first stage gradually disappearing with an increased Al concentration. The effect of particle size d on its burn time t for the prepared alloys is relatively well described by a t ~ dⁿ law, where n is varying in the range of 1.1-1.5 for different compositions.