X-ray diffraction analysis of rust layer on a weathering steel bridge with surface treatment using synchrotron radiation

We have examined the structure of rust layer formed on a weathering steel bridge, to which the surface treatment, employing the effect of Cr-2(SO4)(3) sophisticatedly designed to form the protective goethite (alpha-FeOOH) rust layer which contains a certain amount of Cr, Cr-goethite, was applied in 1996, using X-ray diffraction at SPring-8 synchrotron radiation facility. It was shown that the formation of alpha-FeOOH was promoted and/or crystal growth of gamma-FeOOH was suppressed by the surface treatment. The increase in the protective ability index (PAI) of the rust layer indicates that the protective goethite was predominantly formed under the effect of the surface treatment. In conclusion, it can be said that the surface treatment worked well to promote the formation of the protective goethite rust layer on the weathering steel bridge during the 10-year exposure.