Thermo-mechanical behavior of nano aluminum particles with oxide layers during melting

Molecular dynamics simulations were performed to study the thermo-mechanical behavior of nano aluminum particles coated with crystalline and amorphous oxide layers during melting. The analysis employs the Streitz–Mintmire potential, along with micro-canonical (NVE) and isobaric–isoenthalpic (NPH) ensembles. The effect of particle size in the range of 5–10 nm with oxide thickness in the range of 1–2.5 nm was investigated. The melting phenomenon was characterized using a combination of structural and thermodynamic parameters. Various fundamental processes, including structural changes, stress development, and phase transformations in both the aluminum core and the oxide shell, were examined and quantified systematically. The diffusion of aluminum cations through the oxide layer was also explored. In addition, a structural analysis was applied to determine the stress field in the oxide shell due to the volume dilatation in the aluminum core. In the particle-size range considered here, the oxide layer melts at ~1,100 K, substantially lower than the value for bulk alumina (2,327 K). The oxide thickness exerts a weak influence on the melting temperature of the shell. The aluminum core melts at a temperature considerably lower than its bulk value of 940 K, a situation comparable to that of a pure nano aluminum particle. This study is an important milestone in the development of a multi-scale theory for the ignition and combustion of nano-particulate aluminum.