Structural properties of iron phases formed on low alloy steels immersed in sodium chloride-rich solutions

Products of corrosion were obtained from low alloy steels submitted to total immersion tests in solutions containing sodium chloride at different concentrations, during seven days. In order to properly characterize the adherent (AR) and the non-adherent rusts (NAR), a methodology including room temperature Mössbauer spectrometry, diffuse reflectance infrared Fourier transform spectroscopy, Raman spectroscopy, scanning electron microscopy and X-ray diffraction was addressed. The techniques showed that the AR samples were composed of non-stoichiometric magnetite, goethite, akaganeite and lepidocrocite. The composition of the NAR samples was the same, but with very small amounts of magnetite. Different cell parameters and mean crystallite sizes were found for all phases presented in AR and the NAR samples. The corrosion rates were higher than 580 μm/y. The ratio of the abundances of goethite to the sum of lepidocrocite, akaganeite and magnetite were less than one.