Biodétérioration des structures portuaires en acier : synergie entre la physico-chimie du fer en milieu marin et les micro-organismes sulfurogènes

Mikaël Langumier 1
1 LEMMA - Laboratoire d'Etude des Matériaux par Microscopie Avancée
MEM - Modélisation et Exploration des Matériaux : DRF/IRIG/MEM
Abstract : The aim of this study was to understand the mechanisms involved in marine corrosion of steel structures. These mechanisms are known to be influenced by micro-organisms, in particular by the sulphide-producing bacteria. It was then necessary to couple physico-chemical investigations with techniques of microbiology and molecular biology. In the first part of this work, a laboratory model was designed so as to study the interactions between sulphate-reducing bacteria (SRB) and the main product of the electrochemical corrosion process of iron in seawater, the sulphated green rust, GR(SO42-). We demonstrated that SRB could grow using only the SO42- ions coming from the green rust, thus generating mackinawite FeS as observed in real marine corrosion cases. In the second part, the evolution of the “rust/biofilm” layer that forms on steel in natural seawater was followed for short immersion times, from 1 week to 2 months. The simultaneous monitoring of microbiological and physico-chemical data showed that the influence of SRB was negligible at those early stages. However, the preferential growth of bacteria associated with iron and sulphur could be detected. Moreover, the process influenced by SRB could be detected locally in one case. Finally, in the third part of this work, an electrochemical study of carbon steel in deaerated seawater-like solutions was compared to the results of the physico-chemical and microbiological characterisation of a steel coupon left 11 years in a harbour site. All the results showed that GR(SO42-) was also forming when anoxic conditions were met at the steel surface. The formation of GR(SO42-) however competes with that of FeS and Fe3O4 due to the modifications of the environment induced by micro-organisms. For such long immersion periods, the influence of bacteria seems to decrease. The micro-organisms tend to move away from the inner parts of the rust layer, and then from the metal, to settle the outer parts where more nutrients are available.
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Mikaël Langumier. Biodétérioration des structures portuaires en acier : synergie entre la physico-chimie du fer en milieu marin et les micro-organismes sulfurogènes. Sciences agricoles. Université de La Rochelle, 2011. Français. ⟨NNT : 2011LAROS340⟩. ⟨tel-00717856⟩

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