Atomistic insight into the combustion mechanisms of Al-coated CL-20-based energetic cocrystals using reactive molecular dynamics simulations

Abstract

Context

This work focuses on hexanitrohexaazaisowurtzitane (CL-20)/2,4,6-trinitrotoluene (TNT) and CL-20/benzotrifuroxan (BTF) cocrystals, and aluminum (Al)-coated energetic composites with the core–shell structure were constructed. Reactive molecular dynamics (RMD) simulations were used to study combustion process of Al-coated CL-20-based cocrystal nanoparticles (CL-20/TNT@Al and CL-20/BTF@Al) in O₂ atmosphere, and the effects of Al on the combustion mechanism of CL-20-based cocrystal explosives are analyzed. The findings reveal that these systems undergo volume expansion during the reaction, and the reactions of Al-coated CL-20-based cocrystals initiate earlier than that of pure cocrystal systems. This is attributed to the Al shell could promote internal temperature rise and maintain the energetic state of the explosive molecules, facilitating easier reactions. The variation trends in product quantities during combustion indicate that the Al shell not only alters the initiation time of the combustion reaction but also participates in the combustion process, rapidly consuming reactive nitrogen–oxygen intermediates and promoting the formation of stable small molecular products. Moreover, the differences in CL-20-based cocrystal components lead to varying effects of Al on atomic diffusion, either promotes or inhibits it. Cluster analysis reveals that Al_mO_n clusters generated during the combustion of Al-coated CL-20-based cocrystal explosives exhibit spherical-like three-dimensional structures, while AlₘCₙ clusters adopt two-dimensional network configurations. This study provides a theoretical foundation for understanding the combustion mechanisms of energetic composites.

Methods

All RMD simulations were conducted using the ReaxFF implemented in LAMMPS, and the resulting configurations were visualized via the Ovito package. The time step was 0.1 fs, and the total simulation time was 300 ps. Temperature was controlled by the Nosé–Hoover thermostat, and Newton’s equations of motion were integrated using velocity-verlet algorithm.