Quantifying dispersion and light emission for aluminum powder suspensions with varied surface energy

The dust combustion of aluminum (Al) particles post ballistic impact was studied bi-spectrally in the visible (VIS) and near-infrared (NIR) using high-speed imaging. Powders were delivered loosely via a novel sabot design into a chamber and impacted an anvil at speeds of 1050 m/s. Two identically sized Al powders were studied, one was untreated (UN), the other processed using a thermal annealing and quenching treatment called superquenched (SQ). The SQ Al powder had reduced surface energy compared to UN Al powder, which was induced by the annealing-quenching treatment. Particle dispersion and emission during reaction was quantified by introducing a field emission fraction metric that characterizes the burning powder cloud and relates to particle combustibility. In the case of SQ Al, VIS light emission from dispersed powder decays slower compared to UN Al. High-speed NIR imaging shows UN Al agglomerates resulting in high concentrations of unreacted Al. The differences in powder dispersion and emission were attributed to different combustion regimes and further confirmed by x-ray diffraction analysis of post-burn products, which demonstrated different residue phase compositions. This study demonstrates that a field emission fraction is a quantitative analysis tool to simultaneously evaluate dispersion and emission of dust combustion.