Influence of surface reaction on ignition and combustion of Al-based amphibious energetic composites coated with oxalic acid, B, and Mg clusters

Addressing the inhibitory influence of the oxide layer on the ignition and combustion of aluminium particles stands as one of the pivotal factors in facilitating its utilisation as an amphibious fuel. In this investigation, leveraging the distinctive properties of oxalic acid (OA), which is prone to decomposition and gas generation and holds substantial optimisation potential, surface modification of aluminium particles was conducted in conjunction with boron and magnesium particles. Al-based amphibious energetic composites (AEC) were thereby synthesised. Subsequently, their thermal behaviour, ignition and combustion characteristics, and action mechanism were investigated. The results indicate that the thermal behaviour of AEC samples encompasses dehydration, decomposition, and oxidation stages under amphibious atmospheres (namely, air, water vapour, and their mixtures). The atmosphere exerts a minimal influence on the thermal behaviour. Additives can remarkably enhance the ignition and combustion performance of aluminium particles. Owing to the readily decomposable OA and magnesium oxalate (OM) adsorbed on its surface and the highly reactive Mg particles, the ignition delay time of AEC in amphibious atmospheres is shortened by approximately 45–67 ms. Nevertheless, OA and OM merely function in particle dispersion. Consequently, the oxidising atmosphere in the environment has a substantial impact on the combustion performance of AEC samples. When O₂ is preponderant, the surface reactions of B and Mg clusters on the surface of aluminium particles release heat, thereby facilitating the combustion (the maximum combustion temperature is increased by approximately 600 K). When H₂O is dominant, this combustion-promoting effect diminishes. During combustion, the formation of metal oxides with high melting and boiling points, such as MgO, impedes the contact between the core active metals and oxidising gases, thereby reducing the self-sustained combustion performance of AEC samples. This research will offer crucial insights for the development and application of amphibious metal fuels.