Structure and protective performance of atmospheric corrosion product of Fe-Cr alloy film analyzed by Mossbauer spectroscopy and with synchrotron radiation X-rays

The structure of atmospheric corrosion product of Fe-5 mass%Cr alloy film has been examined by using synchrotron radiation X-rays and gamma-rays for Mossbauer spectroscopy. The relationship between the position of Cr3+ in the atomic arrangement of the rust crystal and the protective performance of the rust layer is discussed. It was found that the rust layer of the FeCr alloy film contains a large amount of ultraftne Cr-goethite. By analyzing the X-ray absorption fine structure at Cr K-edge of the rust layer, we can conclude that Cr3+ is positioned in the double chains of vacant sites in the network of FeO3(OH)(3) octahedra in the goethite crystal. This Cr3+ site might explain the protective performance, owing to dense aggregation of fine crystals with cation selectivity, of the Cr-goethite. (C) 2002 Elsevier Science Ltd. All rights reserved.