In Situ Reactive TEM Study of the Oxidation Kinetics of Aluminum Nanoparticles

This study evaluates the oxidation kinetics of aluminum nanoparticles from 25 to 1000 °C by in situ reactive cell transmission electron microscopy. Combined with TGA-DSC measurement, the oxidation can be divided into three stages from 25 to 1000 °C. The first heating stage is absent any discernible chemistry from 25 to ∼600 °C. A low temperature oxidation stage from ∼600 to ∼800 °C, with an irregular volume increase, where the reaction rate is limited by oxygen diffusing through the alumina shell. A third high-temperature oxidation stage from ∼800 to 1000 °C, corresponding to Al diffusing outward through the alumina shell, ultimately leads to hollow particles. Using quantitative temporal imaging of the evolution of the particle morphology under oxidation conditions, a reaction flux and diffusivity are determined. Comparison with other methods in the literature, we find a clear trend that the measured diffusivity scales with heating rate, which likely explains the wide disparity of diffusivities reported in the literature.