Ennoblement of stainless steel in the presence of glucose oxidase: nature and role of interfacial processes
Résumé
The ennoblement of the free corrosion potential (Ecorr ) of AISI 316L stainless steel which did not occur in synthetic fresh water (SFW), was observed after introduction of glucose oxidase (Gox) and glucose, or of hydrogen peroxide (H2 O2 ). The composition of the surface was monitored using AFM and XPS, a detailed XPS analysis being based on the discrimination between oxygen of organic and inorganic nature proposed in a previous study. In H2 O2 medium, the main changes regarding the inorganic phase were the increase of the oxygen concentration in the passive film, the increase of the molar concentration ratio of oxidized species Feox /Crox and the growth of nanoparticles, presumably made of ferric oxide/hydroxide. In Gox medium, no significant changes were observed in both oxygen concentration and Feox /Crox ratio, but the density of colloidal particles decreased, indicating a dissolution of Fe oxide/hydroxide under the influence of gluconate. In contrast with H2 O2 , in SFW and Gox the amount of organic compounds increased due to the accumulation of polysaccharides and proteins. The influence of glucose oxidase on the ennoblement of stainless steel is not due to indirect effects of H2 O2 through the change of surface composition. The Ecorr ennoblement seems to be directly due to the presence of H2 O2 and to the electrochemical behavior of H2 O2 and related oxygen species. This consideration is important for understanding and controlling microbial influenced corrosion.