Particle combustion dynamics of metal-based reactive materials

Micron-sized particles of aluminum and aluminum-based reactive materials were fed into a CO₂ laser beam where they were ignited. Just prior to entering the CO₂ beam, particles were illuminated by a low-power infrared laser, and their sizes were measured in situ using the intensity of scattered light. Experiments are presented for spherical Al and nanocomposite powders prepared by mechanical milling, including Al·CuO, Al·MoO₃, Al·I₂, Al·B·I₂, Al-wax, and Al-polyethylene. The particle emission signals were recorded and their combustion temperatures were measured optically. In addition, the intensity of molecular AlO emission was monitored. Experiments were performed in air for all materials; additional data for Al combustion in different oxidizers are also presented. For all materials, the effect of particle size on its burn time was observed to be small. No composite material demonstrated consistently higher temperatures or shorter burn times compared to Al powders. For materials with volatile additives (I₂, wax, polyethylene), particle combustion was accompanied by pronounced oscillatory patterns; especially large vapor-phase flames were observed for Al-hydrocarbon composites. Distinct surface reactions were observed for Al·B·I₂ composite particles, which also had the longest burn times compared to other materials. Al·CuO particles fragmented upon ignition while Al·MoO₃ particles burned relatively slowly and without fragmentation.