The detail structure of heavy rust layers with large swelling and laminated layers formed on weathering steel bridges have been investigated by optical microscope and laboratory powder X Ray diffraction (XRD) and synchrotron XRD in SPring 8. Some large gaps (inter layer) and many linearly arrayed voids (LAV) were found along layers. The mass ratio of spinel type iron oxide [mainly Magnetite (Fe 3 O 4 )] in average composition of the whole layer was 30 40 mass. In contrast the mass ratio of spinel in its local parts, i.e. outer layer, inter layer and inner layer position was not higher in common but mass ratio of b FeOOH was higher. Thus we propose a multilayer model structure for these unique rust layers which are made of Spinel Poor, Rich and Poor unit cell structure (SPRaP cell) compartmentalized by LAV.

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Al bearing steels showed high corrosion resistance into coastal environments. The layer of the rusts containing Al was formed on the surface of those alloys after long periods of exposure to the coastal environments, and it was suggested that the Al plays an important role in the corrosion resistivity. In this work, we applied X ray diffraction, electron microscopy, Raman scattering and X ray absorption near edge structure measurements for investigating the state of Al in the rust layer. It was found that the increase in the Al content of those alloys increased amorphous and goethite type iron oxide in the rust. The Al K XANES spectra indicated that the Al substituted goethite, a Fe 1-x Al x OOH, formed on those alloys. This action of Al has an effect on the properties of rust and serves to increase the protective ability of rust layer.

The role of chromium contents on atmospheric corrosion of steel in the environment containing chloride ion was studied by exposure test and electrochemical experiments. It was found that corrosion resistance of 1 chromium steel was lower than that of the steel without chromium in the environment whose concentration of chloride ion was very high by the exposure test. On the other hand, containing chromium increases corrosion resistance in the environment with low chloride concentration. In neutral chloride solution corrosion rate of 1 chromium steel was lower than that of the steel without chromium, but was high in low pH chloride solution. The pH dependence of corrosion resistance of 1 chromium steel corresponded with the corrosion resistance by the exposure test.