Promoting powder suspensions for obscuration by balancing tribocharging and surface energy

The dynamic relationship between surface energy and tribo-electric charging was studied for optical extinction and emission of aluminum powder suspensions. Particles were dispersed via ballistic impact of loose powder in a visually accessible chamber. Flake particulates were studied, including aluminum (Al) and aluminum surface coated with silica (SiO 2 ) (Al@SiO 2 ). High-speed cameras recorded reactive events in air, and optical extinction events in argon environments. Reactive events generate thermal emission analyzed bi-spectrally (NIR and VIS) and non-reactive events block the transmission of light by reflecting or absorbing a reference backlight; reflection and absorption are not deconvoluted in this study. Al@SiO 2 flakes exhibit broad thermal emission compared to Al in reactive suspensions. Also, the SiO 2 surface coating may delaminate from the Al flake during impact thereby exposing Al and resulting in greater fuel consumption compared to Al flakes. Complex reaction mechanisms between silica, alumina, ambient humidity, and air may contribute to broad thermal emission demonstrated by Al@SiO 2 . Measurements of surface energy and calculations of triboelectric charging indicate Al@SiO 2 flakes have greater surface energy than Al flakes, but Al@SiO 2 flakes have ∼2.3x greater repulsion compared to Al flakes. In a non-reactive argon environment, Al@SiO 2 flakes show increased dispersion owing to repulsive tribocharging overpowering surface energy to promote powder suspension. Results reveal the interplay between important properties promoting powder suspensions and their relative consequences. • Flake powders of Al and Al coated with SiO 2 (Al@SiO 2 ) were dispersed via ballistic impact • Upon ignition in air, Al@SiO 2 exhibits broad spectral emission more suited for obscuration • Al@SiO 2 flakes show increased dispersion owing to increased tribocharging • For Al@SiO 2 flakes tribocharging overpowers surface energy to promote powder suspension • Upon impact, Al@SiO 2 flakes delaminate increasing fuel consumption upon reaction in air