Crystalline Rust Compositions and Weathering Properties of Steels Exposed in Nation-Wide Atmospheres for 17 Years

Crystalline rust compositions and weathering properties of steels exposed in nation-wide atmospheres for 17 years have been investigated using X-ray diffraction spectroscopy, with considering the amount of air-borne salt particles. The corrosion loss of the steels, which reflects the corrosion processes during long-term exposure, was related to the rust compositions; especially the corrosion loss was almost proportional to the relative amount of β-FeOOH in the rust layer formed on steels. It can be said that increase in the amount of protective goethite, which is a rust constituent with α-FeOOH structure, and therefore decrease in that of β-FeOOH causes increase in the protective ability of the rust layer. It becomes possible to relate mass ratio between goethite and other active rust constituents including β-FeOOH to the protective performance of the rust layer.