Evidence for the anisotropic oxidation of gas-phase Al nanoparticles

摘要

Transmission electron microscopy was employed to elucidate the morphologies and structures of thermally oxidized gas-phase Al nanoparticles (mean diameter of 10 +/- 3 nm) obtained at various temperatures and oxygen pressures. Exposure of the nanoparticles to oxygen at room temperature followed by heating to high temperatures initially generated an amorphous Al2O3 film on the particles that protected the core from further oxidation up to similar to 1000 degrees C. However, these particles were completely oxidized to gamma-Al2O3 above similar to 1000 degrees C. In contrast, exposing bare, preheated Al nanoparticles to oxygen led to direct oxidation to gamma-Al2O3 at temperatures as low as similar to 575 degrees C. The direct oxidation of Al nanoparticles at 900 degrees C under low oxygen pressures resulted in the growth of worm-shaped gamma-Al2O3 nanoparticles, suggesting anisotropic oxide growth via interfacial oxidation.