High-reactivity energetic micro-units achieved by tightly packing AP and CL-20 onto etched porous Al powder

Aiming at the critical issues of uneven dispersion, inadequate interfacial contact, and significant mass/heat transfer resistance inherent in the mechanical mixing process for traditional solid propellant charging, this study proposes a novel strategy for constructing energetic micro-units through core-shell structural design, with the aim of achieving highly reactive and integrated composites tailored for practical solid propellant applications. Using etched aluminum (Al) powder as the core and ammonium perchlorate (AP) together with hexanitrohexaazaisowurtzitane (CL-20) as the composite shell, Al@AP/CL-20 micro-units with uniform coatings of AP/CL-20 and well-defined core-shell structures were successfully fabricated via solvent evaporation. The thermogravimetric-differential scanning calorimetry (TG-DSC) and combustion analyses indicate that Al@AP/CL-20 energetic micro-units exhibit significantly earlier decomposition peak temperature compared to pure AP, larger and more concentrated exothermic peaks, as well as stronger combustion intensity and higher flame temperature than the Al/AP/CL-20 composite in the physical mixture. The result confirms that the Al@AP/CL-20 composite structure can effectively enhance the synergistic effect between components, thereby improving the performance of the micro-units. Moreover, as the etching time increases, the porosity of the Al powder surface rises, leading to a further enhancement in the combustion performance of the Al@AP/CL-20 energetic micro-unit. In particular, when the Al powder etching time reached 5 h and the mass ratio of Al/AP/CL-20 was 1:2:2, the Al@AP/CL-20 micro-units demonstrated the best combustion performance, with the highest light intensity and a maximum flame temperature of 1094 °C — a 49 % improvement over the physically blended sample (PAAC-2) with the same mass ratio. This is attributed to the well-defined core-shell structure, which significantly shortens mass and heat transfer distances between components, and a better-matched oxygen balance that imparts the best combustion efficiency. The study affirms that the core-shell energetic micro-unit strategy effectively overcomes the limitations of conventional mixing methods and provides a pathway for formulating highly reactive solid propellant with enhanced energy release efficiency.