Hotspot evolution and shock-induced reaction mechanism in aluminum explosives

Aluminum nanoparticles, owing to their high energy density and excellent reactivity, are widely used to enhance the energy release efficiency of explosives. In this study, reactive molecular dynamics simulations were employed to systematically investigate the hotspot evolution and reaction kinetics of aluminum nanoparticles under shock loading. The results show that hotspots predominantly form and evolve along the oxide layer interface, exhibiting a typical “hot shell-cold core” structure. A thicker oxide layer significantly delays the heating and reaction initiation of the aluminum core, with reversible crystal structure transformations observed inside the core. Larger particles facilitate heat accumulation and promote sustained reactions. As the oxide layer thickness increases, the reaction mechanism of aluminum nanoparticles transitions from melting-diffusion and micro-explosion oxidation to an oxidation-diffusion dominated process. A dense nitrogen-containing reaction layer forms on the surface, which suppresses the later-stage reaction. A nonlinear reaction kinetics model based on bond statistics reveals that particles with a thin oxide layer exhibit rapid reaction saturation and are insensitive to shock velocity. Particles with intermediate oxide thickness exhibit a reaction behavior that gradually slows down over time, while those with a thick oxide layer can exhibit accelerated reactions under high-velocity shocks due to enhanced diffusion. Small particles show significantly increased reaction rates at high velocities, whereas large particles tend to slow down due to the thickening of the surface reaction layer. The oxide layer thickness, particle size, and shock velocity exhibit complex competitive and synergistic effects that jointly regulate the initiation, rate, and evolution of aluminum nanoparticle reactions.