(646c) Mechanically-Alloyed Al?Mg Powders With Customized Particle Sizes and Compositions

Adding aluminum to propellants, pyrotechnics, and explosives is a common way to boost their energy density. A number of approaches have been investigated that shorten aluminum ignition delay, increase burn rate, and decrease the tendency of aluminum droplets to agglomerate.  Previous work showed that particles of mechanically alloyed Al∙Mg powders burn faster than similarly sized particles of pure aluminum.  However, prepared mechanically alloyed powders were coarser than fine aluminum commonly used in energetic formulations.  This work is focused on preparation of mechanically alloyed, composite 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 is optimized to prepare equiaxial, micron-scale particles suitable for laboratory evaluations of their oxidation, ignition, and combustion characteristics.  Particle size distributions are measured using low-angle laser light scattering.  Electron microscopy and x-ray diffraction are used to examine particle morphology and phase makeup, respectively.  Combustion of aerosolized powder clouds is studied using a constant volume explosion apparatus.  Combustion of individual particles is studied using a laser ignition setup.  Oxidation and decomposition are studied using thermo-analytical measurements.  For all materials, ignition and combustion characteristics are compared to one another and to those of pure Al.  Additionally, ignition and oxidation characteristics are compared to determine which events lead to particle ignition.  Compositions with improved performance (i.e., shorter ignition delays, higher burn rates, and faster pressurization rates) compared to pure Al are identified.