Oxidation of Aluminum Powders at High Heating Rates

Abstract

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 r ange. 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 pro ject, we use thermogravimetry at heating rates up to 500 K/min (8.3 K/s) to validate and extend the k inetic model currently in use for aluminum oxidation. Oxidation studies 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 project. Activati on energies for individual oxidation steps are generally consistent with previous data obtaine d from low heating rate measurements. Additional oxidation process features are obse rved 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 exper imentally will improve the reliability of current ignition models, as well as establish which oxidation steps identifiable in the low-heating rate thermo-analytical oxidation experime nts cause ignition of aluminum in practical conditions.