Mössbauer Characterization of Rust Obtained in an Accelerated Corrosion Test

Abstract

We have performed drying-humectation cyclical processes (CEBELCOR) on eight A36 low carbon steel coupons in NaCl solutions containing 1×10−2 M and 1×10−1 M concentrations. The main purpose of these experiments is to contribute to the understanding of the conditions for akaganeite formation. Additionally, and with the idea to perform a complete characterization of the rust, this work also considers the formation of other iron oxide phases. The corrosion products were characterized by Mossbauer spectroscopy and X-ray diffraction techniques. Gravimetric analysis demonstrates that the coupons presented high corrosion rates. Magnetite/maghemite was common in the rust stuck to the steel surface, whereas akaganeite was present only in traces. In the rust collected from the solutions, i.e., the rust that goes away from the metal surface easily, a magnetite/maghemite was not present and akaganeite showed up in larger quantities. These results support the idea that high concentrations of Cl− ions are required for the akaganeite formation. We concluded that akaganeite is not easily bonded to the rust layer; this may lead to the formation of a less protective rust layer and to higher corrosion rates.