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.