Synthesis and ignition of energetic CuO/Al core/shell nanowires

Energetic thermites (mixtures of Al and metal oxides), due to their high energy densities, have broad applications in propulsion, thermal batteries, waste disposal, and power generation for micro systems. Reducing the sizes of Al and metal oxides down to the nanoscale has been shown to be effective in increasing their reaction rates and reducing their ignition delays. However, it remains a challenge to create mixtures of Al and metal oxides with nanoscale uniformity. Here we report synthesis and ignition studies on thermites with a new nanostructure, i.e., CuO/Al core/shell nanowires (NWs). The CuO NW cores were synthesized by the thermal annealing of copper films and served as templates for the deposition of Al shells by subsequent sputtering. The advantage of such a core/shell NW structure is that CuO and Al are uniformly mixed at the nanoscale. The onset temperatures of the exothermic reaction of the core/shell NWs were similar to those of nanoparticle (NP)-based thermites in terms of magnitude, insensitivity to equivalence ratios and sensitivity to heating rates. Moreover, the core/shell NW thermites, compared to NP-based thermites, exhibit greatly improved mixing uniformity and reduced activation energy for the thermite reaction.