Energetic characteristics of the Al/CuO core-shell composite micro-particles fabricated as spherical colloids

•Core-shell geometry is clearly shown on SEM images of individual colloids.•Distinct energetic behavior of the core-shell micro-sized metastable composite.•Comparable characteristics to composites with nano-sized Al and CuO constituents.•A solid-state reaction mechanism is proposed for Al and O at the interface.•This new mechanism is different from the literature ones for Al-CuO composites. Metastable intermolecular composites (MICs) exhibit applications in supplying thermal energy to miniature systems, although they are commonly fabricated as powders, films, multi-layers and other heterostructures which desire an effective interface between reactive components but are not colloids and typically immobile. Little information is available in the literature on fabrication and characterization of standing-alone and mobile core-shell MIC micro-particles. In this paper, we report on a wet-chemistry method to synthesize micron-sized spherical colloids of Al/CuO with a core-shell structure. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were employed to characterize the micro-structure and element distribution at the Al/CuO interface, while differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to examine the thermochemical properties of these MIC spherical particles. It was found that for these core-shell micron-sized particles, the onset temperature (about 580⁰C) corresponding to the exothermic reaction is similar to that of the powder mixtures composed of Al and CuO nanoparticles (around 548⁰C), while the activation energy of the former (328 kJ/mol) is much lower than that of the latter (438 kJ/mol). Direct contact and subsequent solid-state diffusion of reactive components at the interface of the Al/CuO core-shell are attributed to these experimental observations. The specific energy release (807 J/g) is however significantly smaller than that of the nano-powder mixtures (1107 J/g) due to the limited thickness of the CuO shell which is originated from the restrictions of the wet chemistry method. Future work includes testing the energetic performance of these core-shell colloids in a liquid or solution ambient.