(458b) Aluminum-Based Thermites Prepared By Staged Milling with Different Process Control Agents

Process control agents (PCAs) serve as an efficient tool for tuning thermite particle morphology and size distribution during mechanical milling. It has been observed that upon interaction with aluminum, hydrocarbons may form carbide and nitride layers in addition to the naturally occurring oxide. These chemical and morphological changes in the surface layers separating aluminum from oxidizers are expected to affect ignition mechanisms of respective thermites. In this study, aluminum-rich thermites (Al·CuO, Al·Fe₂O₃) were prepared by arrested reactive milling in presence of different polar (acetonitrile) and non-polar (hexane) hydrocarbon PCAs. Several samples were prepared and evaluated with different PCA or PCA combinations. In one set of experiments, Al·CuO thermites were milled in different volume of acetonitrile, and very fine, equiaxial composite powders were formed. In the next set of experiments, the thermite powder milled in acetonitrile was recovered and milled in hexane in the second stage. This did not cause agglomeration of the formed powders; instead, further refinement of the produced thermite particles was observed. In another set of experiments, powders of Al and CuO were pre-milled in acetonitrile separately and then blended and milled in hexane. Milling Al in acetonitrile yielded flake-like particles. The flakes of Al milled with CuO during the second stage formed relatively coarse, rounded composite powders. For every combination of process control agents and milling stages, significant differences in particle morphology and size have been observed. It is hypothesized that such differences affect the interfacial contacts between the fuel and the oxidizer, and thus affect kinetics of reactions governing ignition in these materials. Further experiments, including ignition of the prepared powders using an electrically heated filament as well as thermo-analytical experiments will also be presented and discussed.