Reflected shock ignition and combustion of aluminum and nanocomposite thermite powders

A comparison of the ignition and combustion characteristics of Al-Fe ₂O₃ and Al-MoO₃ nanocomposite powders and two sizes of aluminum powder in inert and oxidizing environments was performed in the region behind a reflected shock in a shock tube. Radiation intensity was monitored by photometry, and temporal information on the particle temperatures was obtained using high-speed pyrometry. In addition, emission spectra were collected to identify intermediate species produced during combustion. In inert environments, both thermite materials showed evidence of ignition within 1-2ms at 1400 and 1800K. Particle temperatures during reaction ranging from 2700-3350K were observed, with Al-MoO₃ having generally higher temperatures than Al-Fe₂O₃. Addition of oxygen in the ambient environment reduced ignition times and increased combustion temperatures to 3350-3800K as well, suggesting that heterogeneous reactions can enhance the combustion performance of the thermite materials. In air at 3atm, the nanocomposite thermites and nanoscale aluminum all showed extremely rapid ignition: on the microsecond time scale and under 2000K. The bulk of the material, however, ignited and burned on much longer time scales of the order of 1 millisecond. Bulk nanocomposites were found to ignite as quick or more quickly than bulk, agglomerated nanoscale aluminum and significantly faster than a 5-10 micron aluminum powder.