Oxidation of aluminum powders at high heating rates

A kinetic model of oxidation of aluminum in oxygen has been previously established based on thermal analysis data using heating rates in the 1-40 K/min range. Ignition, on the other hand, involves heating rates that are many orders of magnitude higher, which requires extrapolation of the kinetic predictions. In this study, we use thermogravimetry at heating rates up to 500 K/min (8.3 K/s) to validate and refine the kinetic model of aluminum oxidation. Experiments are conducted in argon/oxygen mixtures. The stepwise aluminum oxidation process reported for lower heating rates is also observed for the higher heating rates addressed in this study. Activation energies for individual oxidation steps are generally consistent with previous data obtained from low heating rate measurements. Additional oxidation process parameters are quantified from the higher heating rate measurements. The overall oxidation model proposed earlier and involving growth of various alumina polymorphs and transformations between these polymorphs is validated in new experiments. The refined oxidation model is successfully used to interpret experiments on aluminum particle ignition in a laser beam, in which the particles are heated at more than 10⁶ K/s.