Nano-composite energetic powders prepared by arrested reactive milling

Highly reactive metastable nano-scale composites of aluminum and metal oxides have been produced by arrested reactive milling (ARM). Aluminum powder has been milled with powders of MoO₃ and Fe₂O ₃. These composites belong to a novel class of energetic materials characterized by an intimate mixing of reactive components on nanometer to atomic scale. Reactive components can be metal/metal oxide pairs or combinations of other materials capable of highly exothermic reactions such as B-Ti or B-Zr. High-energy milling of these components leads to mechanical initiation of the reaction. Highly reactive composites are obtained by arresting this process immediately before the initiation would occur if milling were allowed to proceed. An experimental parametric study of reactive milling in the Al-MoO₃ and Al-Fe₂O₃ systems was conducted to establish at which milling times the reaction is spontaneously initiated under various conditions. An expression for the milling dose - the degree of refinement - was introduced and is an adequate characteristic of the milling progress. Experimental results from the milling parametric study are compared to Discrete Element Modeling currently in development for describing mechanical alloying in SPEX shaker mills. The Discrete Element Models produce an equivalent milling dose that correlates with the experimental results. Samples of nano-composite powders were synthesized by arresting the milling process, and characterized using electron microscopy, x-ray diffraction, and particle size analysis.