Oxidation is a universal process causing metals’ corrosion and degradation. While intensive researches have been conducted for decades, the detailed atomistic and mesoscale mechanisms of metal oxidation are still not well understood. Here using in situ environmental transmission electron microscopy (E-TEM) with atomic resolution, we revealed systematically the oxidation mechanisms of aluminum from ambient temperature to ~ 600 °C. It was found that an amorphous oxide layer formed readily once Al was exposed to air at room temperature. At ~ 150 °C, triangle-shaped Al2O3 lamellas grew selectively on gas/solid (oxygen/amorphous oxide layer) interface, however, the thickness of the oxide layer slowly increased mainly due to the inward diffusion of oxygen. As the temperature further increased, partial amorphous-to-crystallization transition was observed on the amorphous oxide film, resulting in the formation of highly dense nano-cracks in the oxide layer. At ~ 600 °C, fast oxidation process was observed. Lamellas grew into terraces on the oxide/gas interface, indicating that the high temperature oxidation is controlled by the outward diffusion of Al. Single or double/multi-layers of oxide nucleated at the corners of the terraces, forming dense γ’-Al₂O₃, which is a metastable oxide structure but may be stabilized at nanoscale.

中文翻译：

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铝纳米粒子的温度依赖性原子和中尺度氧化机理的原位观察

氧化是导致金属腐蚀和降解的普遍过程。尽管已经进行了数十年的深入研究，但金属氧化的详细的原子和中尺度机理仍未得到很好的理解。这里就地使用在具有原子分辨率的环境透射电子显微镜（E-TEM）中，我们系统地揭示了铝从环境温度到〜600°C的氧化机理。发现一旦在室温下将Al暴露于空气，就容易形成非晶氧化物层。在约150°C时，三角形的Al2O3薄片在气/固（氧气/非晶态氧化层）界面上选择性生长，但是，氧化层的厚度缓慢增加主要是由于氧气的向内扩散。随着温度的进一步升高，在非晶氧化物膜上观察到部分非晶-结晶转变，导致在氧化物层中形成高密度的纳米裂纹。在〜600°C，观察到快速氧化过程。薄片状生长在氧化物/气体界面的阶地上，表明高温氧化是由Al向外扩散控制的。单层或双层/多层氧化物在台阶角处成核，形成致密的γ'-Al₂ O ₃，其为亚稳定的氧化物结构，但可以在纳米级稳定。