Mossbauer spectroscopic study of rust formed on a weathering steel and a mild steel exposed for a long term in an industrial environment

The rusts formed on mild steel (15-year exposure) and weathering steel (32-year exposure) exposed to an industrial environment have been characterized by means of X-ray diffraction technique and Fe-57 Mossbauer spectroscopy. By using an X-ray diffraction method, it is suggested that the rusts formed on both steels consist of the crystalline alpha-FeOOH, gamma-FeOOH and an X-ray amorphous phase. which gives no peak to X-ray diffraction pattern, The amount of the X-ray amorphous phase exceeds 50% of the total amount of the rust. The Fe-57 Mossbauer spectra observed at 10 K indicate that the rust contains only alpha-FeOOH, gamma-FeOOH and Fe3-deltaO4 (gamma-Fe2O3) for mild steel, and only alpha-FeOOH and gamma-FeOOH for weathering steel. The X-ray amorphous substance in the rust layer formed on mild steel possesses the structures of mainly alpha-FeOOH showing superparamagnetism owing to its small particle size. and Fe3-deltaO4 (gamma-Fe2O3). Them are contained both in the inner rust layer and in the outer rust layer. The X-ray amorphous phase in the rust layer formed on weathering steel is mainly alpha-FeOOH.