Carbon steel is widely considered as a candidate material for the construction of spent fuel and high-level waste disposal canisters. In order to investigate corrosion processes representative of the long term evolution of deep geological repositories, two in situ experiments are being conducted in the Mont-Terri rock laboratory. The iron corrosion (IC) experiment, aims to measure the evolution of the instantaneous corrosion rate of carbon steel in contact with Opalinus Clay as a function of time, by using electrochemical impedance spectroscopy measurements. The Iron Corrosion in Bentonite (IC-A) experiment intends to determine the evolution of the average corrosion rate of carbon steel in contact with bentonite of different densities, by using gravimetric and surface analysis measurements, post exposure. Both experiments investigate the effect of microbial activity on corrosion. In the IC experiment, carbon steel showed a gradual decrease of the corrosion rate over a period of 7 years, which is consistent with the ongoing formation of protective corrosion products. Corrosion product layers composed of magnetite, mackinawite, hydroxychloride and siderite with some traces of oxidising species such as goethite were identified on the steel surface. Microbial investigations revealed thermophilic bacteria (sulphate and thiosulphate reducing bacteria) at the metal surface in low concentrations. In the IC-A experiment, carbon steel samples in direct contact with bentonite exhibited corrosion rates in the range of 2 µm/year after 20 months of exposure, in agreement with measurements in absence of microbes. Microstructural and chemical characterisation of the samples identified a complex corrosion product consisting mainly of magnetite. Microbial investigations confirmed the limited viability of microbes in highly compacted bentonite.

中文翻译：

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与放射性废物地质处置有关的粘土环境中碳钢的腐蚀，蒙特里岩石实验室（瑞士）

碳钢被广泛认为是制造乏燃料和高级别废物处理罐的候选材料。为了研究代表深部地质储层长期演化的腐蚀过程，正在蒙特-特里岩石实验室进行两个原位实验。铁腐蚀（IC）实验旨在通过电化学阻抗谱测量法测量与Opalinus Clay接触的碳钢瞬时腐蚀速率随时间的变化。膨润土中的铁腐蚀（IC-A）实验旨在通过暴露后的重量分析和表面分析测量，确定与密度不同的膨润土接触的碳钢平均腐蚀速率的演变。这两个实验都研究了微生物活性对腐蚀的影响。在IC实验中，碳钢在7年的时间内腐蚀速率逐渐降低，这与保护性腐蚀产物的不断形成是一致的。在钢表面上发现了由磁铁矿，马基金刚石，羟基氯化物和菱铁矿组成的腐蚀产物层，以及一些痕量的氧化物质，如针铁矿。微生物研究表明，金属表面的嗜热细菌（硫酸盐和硫代硫酸盐还原菌）浓度低。在IC-A实验中，与膨润土直接接触的碳钢样品在暴露20个月后显示的腐蚀速率为2 µm /年，这与不存在微生物的测量结果一致。样品的微观结构和化学特性鉴定出主要由磁铁矿组成的复杂腐蚀产物。微生物研究证实了微生物在高密度膨润土中的生存能力有限。