Structural analysis of corrosion product of Fe-Cr alloy film using synchrotron radiation

Yamashita, Masato*; Konishi, Hiroyuki; Takahashi, Masamitsu; Mizuki, Junichiro; Uchida, Hitoshi*

A rust layer on a weathering low-alloy steel has strong protective ability for atmospheric corrosion of the steel. In order to control the rust layer on steels, it is so important to know the detailed structure of rust and relate it to the protective ability of the rust layer. Especially, the position of atoms of the alloying elements in the rust layer directly control the structure and properties of the rust layer. We tried to find the atomic arrangement of the rust layer of Fe-Cr alloy film covered with thin film of electrolyte using synchrotron radiation. Grazing incidence X-ray diffraction and Mssbauer spectra showed that the rust layer was composed of -FeOOH and ultra-fine -FeOOH. By examining EXAFS spectra, Cr coming from Fe-Cr alloy film would be present in the -FeOOH. Some of Cr would be present between Fe-0-OH octahedron as interstitial atoms, as well as substituting Fe lattice site in the octahedron.