Investigation of Burning Aluminum in Oxygen-Enriched Atmospheres Through Microanalysis Techniques

Promoted-ignition testing of 3.2 mm diameter aluminum rods in high purity oxygen was performed. The rod and detached drops of both self-extinguished and water quenched samples were examined using scanning electron microscopy and electron probe microanalysis to analyze the physical structure of the sample and gather compositional data. A comparison of the micrographs of self-extinguished and quenched samples reveals clear differences in the extent of melted and re-solidified (unreacted) material and the thickness of the oxide layer, highlighting the effect of cooling rate on the burning system. A qualitative physical model for the burning of bulk aluminum in gaseous oxygen is presented. The model, incorporating a molten drop growth and detachment cycle, is based on an initial heterogeneous burning phase leading to a second phase of combined heterogeneous and homogeneous burning.