Enhanced energy performance from core–shell structured Al@Fe2O3 nanothermite fabricated by atomic layer deposition

Abstract

The energy performances of nanothermite materials are dependent on the mass transport, diffusion distance, and interfacial contact area between the fuel and the oxidizer. In this work, we utilize an atomic layer deposition (ALD) technique to deposit Fe₂O₃ directly onto the surface of Al nanoparticles, producing a core–shell structured nanocomposite (Al@Fe₂O₃). Quartz crystal microbalance measurement and mass gain analysis reveal that the average Fe₂O₃ film growth rate is 0.12–0.13 nm per cycle. The thickness of the Fe₂O₃ layer deposited on the Al nanopowder can be precisely controlled by adjusting the number of ALD cycles. Structural characterization results demonstrate complete encapsulation of Al nanoparticles by conformal γ-Fe₂O₃ layers and confirm the formation of core–shell nanocomposites. The energy release and combustion properties of the nanothermites are investigated by differential scanning calorimetry and laser ignition tests. Compared to mechanically mixed Al–Fe₂O₃ nanopowders, the Al@Fe₂O₃ nanothermite has a lower onset temperature and a higher energy output. Besides, the thermite reaction of Al@Fe₂O₃ is several times faster than that of a mixture of Al–Fe₂O₃ nanopowders. The improved energy performance is mostly attributed to the uniform distribution of Al and Fe₂O₃ on the nanometer scale, which effectively reduces the diffusion distance and maximizes the interfacial contact area between the oxidizer and the fuel.