Molecular Dynamics Simulations of the Oxidation of Aluminum Nanoparticles using the ReaxFF Reactive Force Field

We performed ReaxFF-molecular dynamics (MD) simulations of the oxidation of aluminum nanoparticles (ANPs) at three different temperatures (300, 500, and 900 K) and two different initial oxygen densities (0.13 and 0.26 g/cm³) to elucidate the mechanism of oxidation kinetics of the ANPs and to study the oxidation states in the oxide layer. Our result shows that the mechanism of the oxidation of the ANPs is as follows: hot-spots and high-temperature areas are created by adsorption and dissociation of oxygen molecules on the surface of the ANPs; void spaces are generated because of hot-spots and high-temperature areas; the void spaces significantly lower a reaction barrier for oxygen diffusion (by up to 92%) and make this process exothermic. Subsequently, an oxide layer is developed by this accelerated oxygen diffusion. Our results also indicate that the oxidation of the ANPs depends on combined effects of the temperature and the oxygen gas pressure because such conditions have effects on not only the oxide layer thickness but also the density of the oxide layer. These ReaxFF results are in good agreement with available experimental literature on aluminum oxidation kinetics.