Fe(O,OH)₆ network structure of rust formed on weathering steel

X-ray absorption fine structure (XAFS) analysis and transmission electron microscopy (TEM) have been used for investigating the atomic structure and microstructure of rust formed on a weathering steel and a relevant iron-chromium alloy. The XAFS results have shown that the atomic structure of the rust is an Fe(O,OH)₆ network, which is formed during corrosion. From comparison of XAFS spectra for rust formed under different conditions, it has been shown that the Fe(O,OH)₆ network structure evolves in the process of corrosion and a small amount of an alloying element such as chromium modifies the evolution process and morphology of the rust. Observation by TEM has revealed that rust formed on the weathering steel consists of heterogeneous but mainly very fine α-FeOOH, which is caused by chromium.