Effects of Particle Size and Oxide Shell Thickness on the Oxidation Characteristics of Core–Shell Aluminum Nanoparticles Using Molecular Dynamics Simulation

Aluminum nanoparticles (ANPs) possess a core–shell structure, yet the coupled roles of atomic stress and interfacial charge transfer in their slow-heating oxidation remain elusive. This study employs ReaxFF molecular dynamics simulations to investigate the oxidation of six core–shell ANPs with different particle sizes (5–10 nm) and shell thicknesses (0.5–2.0 nm) from 300 K to 1400 K. Results reveal that the stress evolution dictates the oxidation pathway. Thin shells (0.5–1.0 nm) undergo a compressive-to-tensile stress transition, leading to shell rupture at ~1060 K and subsequent outflow and rapid oxidation of Al into clusters, while thick shells (1.5–2.0 nm) maintain compressive confinement, preventing rupture but resulting in incomplete oxidation (58–84%). Mean squared displacement indicates earlier atomic diffusion onset for thin-shell particles (~7 ps) compared to thick-shell ones (~15 ps). Significantly, interfacial charge redistribution provides the electronic driving mechanism: thin shells facilitate charge homogenization and electron loss, lowering diffusion barriers, whereas thick shells sustain distinct charge separation, impeding atomic migration. These findings provide a theoretical basis for the atomic-scale stress–charge–diffusion coupling mechanism, offering crucial insights for the safety assessment and structural design of oxidation-resistant ANPs.