AC corrosion behaviour: characterization of corrosion products by in-situ Raman spectroscopy

摘要

The corrsion on mild steel induced by alternative current (AC) in artificial groundwater under cathodic protection was studied. For this sake, in-situ Raman spectroscopy technique was used to identify the corrosion products that cover the electrode surface. The starting idea is to know in what extent AC signal has a role in red-ox processes of corrosion products during AC perturbation in various test solutions. What kind of the corrosion products will be formed on the mild steel protected by cathodic protection with a large AC signal? Beside, since there is a deep excursion of potential between the hydrogen evolution and the oxygen formation potential domain at each AC period, the corrosion products may be alternatively transformed into a reduced and oxidized species.rnResults showed that in the presence of chloride ions, green rust products were detected at small AC amplitude. In contrast, with large AC amplitude,the magnetite was observed. The formation of this species was allocated to a marked alkalinisation of the electrolyte medium at the very vicinity of steel surface by the reduction of electrolyte medium. Obviously, the anodic polarization does not induce a significant acidification of the medium. It was shown finally that the alternative signal at 50 Hz is too fast to transform at each cycle the corrosion products, but AC perturbation accelerates the corrosion process.