Simulations on the oxidation of Al-Mg alloy nanoparticles using the ReaxFF reactive force field

Nanoalloy holds multiple complex morphologies in combustion. However, the underlying mechanism, which is crucial to advance technical application of the nanoalloy, remains a challenging mystery. Herein, we performed a ReaxFF reactive molecular dynamics simulation on Al-Mg alloy nanoparticles (AMNPs) as a case study to further analyze oxidation behavior. Results showed that the evolution of AMNPs in combustion can be divided into three stages: (1) AMNPs first undergo phase separation and aggregate into Mg and Al phases; (2) Mg atoms rapidly diffuse to the surface and are oxidized; (3) Oxygen atoms diffuse inward and oxidize Al atoms. The inward diffusion of oxygen atoms is particularly hindered at the interface between Mg oxide shell and Al oxide layer. AMNPs prefer to form internal hollow structures at lower temperature and high oxygen concentration. The outward diffusion of Mg atoms causes the core to be gradually hollowed out. The spilled Mg atoms are oxidized and attached to the surface of alumina. The structure of Mg oxide (surface layer)-Al oxide (middle layer)-hollow (core) is finally formed. In addition, micro-explosion and external Mg oxide shell inhibit the agglomeration of nanoparticles. The study provides insight into the complex interactions between Al-Mg nanoalloy and oxygen.