Oxidation of aluminum powders at high heating rates

A kinetic model of oxidation of aluminum 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, and experimental work under these conditions is ongoing. In this project, we use thermogravimetry at heating rates up to 500 K/min (8.3 K/s) to validate and extend the kinetic model currently in use for aluminum oxidation. Oxidation studies are conducted in argon/oxygen mixtures. The step-wise aluminum oxidation process reported for lower heating rates is also observed for the higher heating rates addressed in this project. Activation energies for individual oxidation steps are generally consistent with previous data obtained from low heating rate measurements. Additional oxidation process features are observed at the higher heating rates and interpreted in the framework of the general concept proposed earlier and involving growth of various alumina polymorphs and transformations between these polymorphs. It is expected that the wider range of heating rates covered experimentally will improve the reliability of current ignition models, as well as establish which oxidation steps identifiable in the low-heating rate thermo-analytical oxidation experiments cause ignition of aluminum in practical conditions.