Effect of Particle Morphology and Added Gallium on Reactivity of Aluminum Powders

Micron-sized powders of neat aluminum and aluminum combined with 5 wt% gallium are prepared as flakes and spherical composites by emulsion-assisted milling. Such powders are of interest as high-energy-density fuel additives to solid propellants, explosives, and pyrotechnics. Added gallium does not affect the size or shape of the prepared composites; it also does not change appreciably the oxidation kinetics of the prepared powders. All milled powders ignite readily when coated on an electrically heated filament, unlike the starting aluminum powder. Powders with added gallium ignite at slightly lower temperatures when heated rapidly. The liquid metal embrittlement effect due to added gallium might have caused a smaller microstrain in the refined, milled powders. However, it does not affect the oxidation. Instead, it is proposed that added gallium alters the natural amorphous alumina film, affecting its transition to a crystalline γ-phase during rapid heating, and thus affecting the powder ignition.