Abstract
Use of reflected polarized light and crossed nicols in microscopic observation of the polished crosssection of the rust makes it possible to distinguish optically active layer (FeOOH) and optically isotropic one in the rust. In the atmospheric corrosion resisting steel, the metal surface is almost completely covered with the optically isotropic layer after long periods of exposure to the atmosphe e
The experimental results of X-ray diffraction and cathodic reduction of the rust indicated that this optically isotropic layer was composed of amorphous spinet type iron oxide. This amorphous iron oxide is considered to be a polymeric ol-compound. The enrichment of Cu, Cr and P in the optically isotropic layer was found by means of electron probe microanalysis.
It was deduced that the significant corrosion resistance of atmospheric corrosion resisting steels was attributed to the formation of this amorphous layer. Alloying elements, such as Cu, Cr and P, are possibly beneficial to the formation of this layer.
