Atomic Insight into the Oxidation Mechanism of a Core-Shell Aluminum Nanoparticle: Atomic Diffusion or Micro-Explosion?

B Wu and XX Wang and YB Zhu and HW Wu and AM He and HA Wu and P Wang, JOURNAL OF PHYSICAL CHEMISTRY C, 127, 16781-16791 (2023).

DOI: 10.1021/acs.jpcc.3c02577

Aluminum nanoparticles (ANPs) arean effective and economical additivein various energy conversion applications. In the present work, ReaxFFmolecular dynamics simulations are performed to reveal the underlyingoxidation mechanism of the natural core-shell ANPs with variousoxygen concentrations, particle sizes, and shell thicknesses. Theoxidation of ANPs is initiated by the atomic diffusion of Al and oxygenthrough the oxide shell, and the subsequent oxidation can be dividedinto three distinct modes dependent on the initial conditions. Fora small size parameter M (ratio of core radius toshell thickness), the particles remain intact during the whole oxidationprocess via atomic diffusion. For a large size parameter M, cracks may appear on the oxide shell as the melted Al expands,which provides pathways for Al-oxygen diffusions. Under highoxygen concentrations, the extreme self-heating rate caused by quicklyexothermic reaction leads to the violent evaporation of Al and subsequentmicro-explosion of ANPs, which first confirms the experimental observationsfrom the atomic perspective. This work reveals a fundamental mechanismfor describing the oxidation of ANPs and provides a guideline forimproving the combustion efficiency of ANPs, that is, the micro-explosionscan be promoted by increasing the initial particle size parametersand oxygen concentrations.

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