Chemical Engineering Journal Advances (Aug 2022)
Solution synthesis of core-shell n-Al@CuO based on electrostatic self-assembly for enhanced energetic performance
Abstract
Ignitable micro- and nano-sized energetic particles are desirable in MEMS (micro-electromechanical system) devices in delivering energy to a target and producing heat in-situ. It is challenging however to fabricate these particles due to the incomplete mixing between the fuel and oxidizer during the manufacturing process and its sensitivity to external stimuli. The core-shell structure is considered one of the most promising microstructures as it provides a standalone reactive system composed of fuel and oxidizer packed in a single assembly. A wet-chemistry synthesis route was developed to fabricate spherical core-shell Al/CuO MICs (metastable intermolecular composites). X-ray diffraction (XRD) and electron microscopy results revealed how synthesis parameters control the fabrication of the final product. By changing the ammonia content during the synthesis, the structure of the final product could be “switched” between a well-mixed nanocomposite and individual nanosized core-shell spheres, likely due to electrostatic forces between Al nanoparticle and intermediate compounds of Cu and ammonia. Differential scanning calorimetry (DSC) results indicated that the as-synthesized core-shell Al/CuO reduced the onset temperature by 8 °C and peak temperatures by 20 °C compared to Al/CuO nanoparticles physically mixed by ultrasonication due to the proximity between fuel and oxidizer nanoparticles. The activation energy of core-shell Al/CuO was also reduced by about 20 kJ/mol compared to physically mixed products. More importantly, the core-shell nanoparticles showed a significantly reduced ignition delay and homogeneous combustion behavior, which was different from physically mixed Al/CuO. The wet-chemistry method enables bulk production of both Al/CuO nanocomposite and core-shell nanostructures for larger-scale industrial applications.
