Thermally induced surface changes in aluminium-iron oxide thermites

Abstract

The aluminium and iron oxide surfaces of Al-Fe₃O₄ thermite in powder and pressed pellet form were studied before and after accelerated ageing at 180° C by X-ray photoelectron spectroscopy. The Al₂O₃ surface film thicknesses on aluminium metal were deduced from the intensity ratio of aluminium K L L Auger signals induced by X-ray radiation on Al₂O₃ and aluminium metal. Based on the mean free path of 1.65 nm for aluminium K L L Auger electrons, the oxide thickness on aluminium flakes before mixing with Fe₃O₄ was estimated to be 0.8 to 0.9 nm. A slight oxidation was observed on the aluminium surface after mixing with Fe₃O₄ at room temperature. Hot pressing of this mixture at 425° C for 7 min increased the oxide film to 3.1 nm. This surface oxide film seemed to protect the aluminium metal, and further ageing at 180° C did not cause significant oxide growth.