Shock-Induced Anisotropic Metal Combustion

The progress of surface reactions can be largely impacted by anisotropic energy transfer. Here, we carried out reactive molecular dynamic simulations on aluminum nanoparticles in shock waves up to 8 km/s. From the analysis of particle morphological evolutions, heat and mass transfer, and reaction products, it is found that the shock-induced effect strongly correlates with flow velocity. We further elaborate oxidation mechanisms into three modes: Diffusion oxidation (<2 km/s), anisotropic oxidation (2-5 km/s), and microexplosion oxidation (>5 km/s). The first mode corresponds to the typical isotropic mechanism of nanoparticles. In the second mode, shock induces an anisotropic temperature gradient via molecular collisions and triggers the ignition in one side. Further increasing the flow velocity, severe dispersion of small AlxOy clusters is identified as a microexplosion event. These three oxidation modes dedicate to interpret the effect of translational energy on surface reactions and supplement the current oxidation theory.