Atomistic insight into shell-core evolution of aluminum nanoparticles in reaction with gaseous oxides at high temperature

Aluminum nanoparticles (ANPs), as an economical and effective metal fuel, are widely applied in energetic formulations. The objective of this research was to gain insights into the oxidation of ANPs in gaseous oxides (CO2, CO, NO2, and NO). The reactive molecular dynamics (RMD) simulations were performed to elucidate the detailed mechanisms of surface oxidation, chain-like products formation, and hollow formation in the evolution of ANPs. The O atoms in gaseous oxides are adsorbed on the ANPs' surface followed by the cleavage of O-C/N bond. The nucleation and growth of chain-like products occur in dense gaseous oxides. The four forms of chain products include tilted chain, twisted chain, branched chain, and cyclic chain were observed in CO atmosphere. A similar chain structure is also formed in NO atmosphere, but the chain length is significantly reduced. The oxide shell of ANPs is formed and expands rapidly in CO2 atmosphere, resulting in voids between oxide shell and Al core. Al atoms are transported from the core to the oxide shell through a bridge composed of Al atoms. The Al core gradually diffused outward and was eventually hollowed out. In addition, the final product has carbon deposits (C-48 and C-98) on the surface and core.