Investigation of steel corrosion in MX80 bentonite at 120°C

Abstract

Corrosion experiments were performed on two metallic substrates, a ferritic–pearlitic steel (P285NH) and a ferritic one (Armco), in silicate environment during 30 days at 120°C. Corrosion products were characterized in terms of morphology (scanning electron microscope and transmission electron microscopy), composition (energydispersive X‐ray spectroscopy) and structure (µ‐Raman, selected area electron diffraction, X‐ray absorption near edge structure). Results show a nanometric inner layer made of compact and adherent nanocrystallized magnetite with, locally a thickness up to several micrometers due to the metal microstructure. An outer layer of Fe‐rich phyllosilicate, smectite and serpentine, more porous than the inner one and poorly adherent is observed around both the samples.

13C isotopic labeling to decipher the iron corrosion mechanisms in a carbonated anoxic environment

“…Moreover, nanometric nodules of magnetite were detected by TEM inside the inner part of the siderite layer. [22,23] After 3 months, the same layout was observed with a bilayer composed of carbonate phases. The only difference was due to the formation of a local corrosion area at the metal/corrosion layer interface containing iron silicate phases.…”

“…Over time the diffusion limitation of the reactive species could be measured by the authors thanks to EIS spectroscopy and the layers became more compact after the SEM observations. Last, a study was conducted by Lotz et al [22,23] at 120°C in a Callovo-Oxfordian (COx) porewater containing carbonate in solution. After 1 month it was shown that the bilayer of siderite containing calcium was still present at such duration showing a compact morphology on both ferritic and ferrite-pearlitic metallic samples.…”

“…This allowed us to conclude that at this stage the corrosion front was located in these local corrosion areas. [23] Summarizing the results of the experiments performed in carbonated solutions presented in the literature, whatever the temperature, the protection mechanisms presented are based on the control of the diffusion of the carbonate species through the corrosion layer acting as a diffusion barrier toward the metal. This leads to the mass transfer limitation and the decrease of the anodic reaction.…”

Formation of Iron Sulfides on Carbon Steel in a Specific Cement Grout Designed for Radioactive Waste Repository and Associated Corrosion Mechanisms

“…Fe is not present in these particles and consequently they do not correspond to corrosion products. Fe-rich phyllosilicates, which were for instance obtained on steel in bentonite at 120 °C [26], did not form in the experimental conditions considered here. The thickness of the corrosion product layer can be estimated from the Fe and S maps at about 20 µm.…”

Modeling and simulation of ductile damage in forged steel used to encapsulate high-level radioactive waste

“…Several scientific studies have been conducted on the corrosion of metallic structures within the context of the disposal of HLW (Guo, 2020). For the case of steel containers, several works have been published studying the effect of corrosion on their long-term behavior (Bulidon, 2021), (Ghahari, 2012), (Lotz, 2021), (Zhang, 2019). The corrosion process of a P285NH overpack in in-situ repository conditions has been studied in (Necib, 2017).…”