Réaction de réduction de l'oxygène sur les aciers inoxydables en eau de mer naturelle. Influence du biofilm sur les processus de corrosion

iofilm development on stainless steels immersed in natural seawater can have prejudicial consequences on the resistance of these materials to corrosion . The goal of the present study was to get more precise information on the corrosion processes, and especially on the oxygen reduction reaction. As the reaction is linked to the stainless steel surface state, the characterisation of the oxides films (composition, structure, thickness...) is essential to understand the mechanisms and the oxygen reduction kinetic. The first aim of the study has been to correlate the oxygen reduction processes with the characteristics of the oxides layer as a function of the alloy surface treatment (mechanical polishing, electrochemical passivation and prereduction, chemical treatment with some acids or with hydrogen peroxide). The second stage has consisted in following the evolution of the oxygen reduction processes and of the characteristics of the oxides layer with the aging of stainless steels in natural and artificial seawaters. One major biofilm effect appears to be the production of hydrogen peroxide at a concentration level which induces modifications of the oxides layers and, consequently, of the evolution of the oxygen reduction kinetics as well as of the open circuit potential. Electrochemical techniques (voltammetric analysis at rotating disk and ring-disk electrodes, coulometry) combined with a surface analytical method by X-ray photoelectron spectroscopy have been used. The characterisation of the biofilm required the use of microscopy (scanning electronic microscopy, epifluorescence microscopy) and microbiological methods (cultures). The in-situ detection of hydrogen peroxide formed inside the biofilm has been performed with a microelectrode and the results were confirmed with enzymatic methods.