In Situ Multiscale Study of Iron Oxidation at High Temperatures

Although high-temperature oxidation of metals results in significant failure of structure materials, in situ understanding of these processes and developing improved strategies are still very limited. Herein, using environmental scanning electron microscopy (ESEM), environmental transmission electron microscopy (ETEM), and X-ray photoelectron spectroscopy (XPS), we report the in situ dynamic high-temperature oxidation behaviors of iron in O₂, H₂O, and O₂ + H₂O atmospheres, respectively. The results demonstrate that an oxygen-rich environment (1.6 mbar) leads to transient formation of polycrystalline Fe₃O₄ without passivation effects on further oxidation, while sparse oxygen environments (10^-3 mbar) promote formation of a uniform thin passivation layer of Fe₃O₄, protecting itself from further oxidation in ambient air. In contrast to O₂, the H₂O vapor accelerates oxidation, and the products consist of Fe₃O₄ and FeOOH. These in situ results give insights into designing technically universal antioxidation strategies.