FUEL-RICH ALUMINUM-METAL FLUORIDE THERMITES

Nanocomposite thermite powders using aluminum as fuel with cobalt and bismuth fluorides as oxidizers were prepared by arrested reactive milling. Each material contained 50 wt% of aluminum and 50 wt% of a fluoride, resulting in fuel-rich compositions. The reactions in the prepared powders were characterized by thermo-analytical measurements; powders were ignited as coatings on an electrically heated filament and by electrostatic discharge. It was observed that the exothermic reactions begin in aluminum-metal fluoride thermites at lower temperatures than in any previously prepared reactive nanocomposites based on aluminum. Redox reactions in Al.CoF2 and Al.BiF3 nanocomposite started around 200 and 250 degrees C, respectively. The results suggest that the initial reactions are rate-limited by the decomposition of fluorides. In the oxygenated environments, metals generated by reducing the starting fluorides oxidize readily. The newly formed oxides are rapidly reduced by excess aluminum, accelerating aluminum oxidation at low temperatures. The low-temperature thermally activated reactions lead to low ignition temperatures for the powders heated on the filament. Despite the low ignition temperatures, both preparedmaterials were relatively insensitive to ignition by an electric spark, making them attractive components of advanced energetic formulations.