Fe(O,OH)6 network structure of rust formed on weathering steel surfaces and its relationship with corrosion resistance

Weathering steel, when exposed outdoors for a few years, forms a protective layer resulting in reduction of the corrosion rate. The state of rust is fundamental for understanding its mechanism, but the structure and its relationship with the mechanism have not been understood. In this study, a new approach was applied to reveal the nano-structure of rust using x-ray absorption fine structure (XAFS) analysis, X-ray anomalous scattering, reverse Monte-Carlo method, and transmission electron microscopy (TEM). It has been shown that the Fe(O,OH)6 network composed of octahedrons of FeO6 octahedrons evolves during the process of corrosion and that a small amount of additional elements changes its process and affects the final morphology.