Microbiall y induced corrosion of carbon steel 12020 and titanium alloy TiGr7 under anaerobic conditions

摘要

The main goal of the present study was to assess the impact of microbial activity on corrosion behaviours of carbon steel 12020 and titanium alloy TiGr7 proposed as a canister material for high-level radioactive waste in a deep geological repository. The biocorrosion of canister materials was studied under strictly anaerobic conditions and the structural differences of bacterial communities depending on material were identified. Sticks of carbon steel 12020 and titanium alloy TiGr7 were placed into experimental cells filled with groundwater naturally containing sulphate reducing bacteria (SRB) or with synthetic bentonite pore water mixed with the same groundwater containing SRB. In parallel, the experiments were performed under sterile conditions in order to evaluate the contribution of microbially induced corrosion to overall corrosion. Corrosion behaviours were studied using electrochemical impedance spectroscopy and surface analysis in several experiments lasting from 27 to 190 days. The difference between corrosion potentials of carbon steel 12020 in sterile system and system containing bacterial communities was observed. The corrosion potential becomes anodic for the systems containing bacteria (approximately difference 60 mV) due to the presence of microorganisms on the surface of carbon steel samples. The structure of microbial communities of water and biofilm samples obtained from the two materials tested was assessed by amplicon sequencing of 16S rRNA region. The relative changes of several functional bacterial groups (sulphate-, nitrate-, and iron-reducing bacteria) were studied by quantitative PCR. The biofilm formation was observed by electrochemical impedance spectroscopy on carbon steel 12020 that was placed in the groundwater containing sulphate reducing bacteria. The increase in sulphate-, nitrate-, and iron-reducing bacteria in water samples was observed. The structure of bacterial community differed depending on material tested and on water type used (groundwater containing bacteria vs. with synthetic bentonite pore water mixed with the same groundwater).