Corros. Mater. Degrad., Volume 5, Issue 2 (June 2024) – 7 articles

The disposal of high-level radioactive waste (HLW) and spent nuclear fuel (SF) presents a unique challenge for the prediction of the long-term performance of corrodible structures since the HLW/SF canisters are expected, in some cases, to have lifetimes of one million years or longer. Various empirical and deterministic models have been developed over the past 45 years for making predictions of the long-term corrosion behaviour, including models for uniform and localized corrosion, environmentally assisted cracking and microbiologically influenced corrosion. As well as process models focused on specific corrosion mechanisms (described in Part 1 of this review), there is also a need for performance assessment models as part of the overall analysis of the safety of a deep geological repository (DGR). Performance assessment models are often based on simplified or abstracted process models. The manner in which various international waste management programs have predicted the long-term performance of HLW/SF containers with copper, steel, Ni and Ti alloy corrosion barriers is discussed. Performance assessments are repeated periodically during the development and implementation of a DGR, and the corrosion models are constantly updated in light of new mechanistic understanding and/or more information about the deep geological environment. Two examples of how the container performance assessment models evolve over time are also described. Performance assessment models cannot easily be validated, so it is important to build confidence in the long-term predictions using other methods, including natural analogues and large-scale in situ tests and the use of complementary models. Full article

This paper addresses the interplay between electrical fields in the human body and the corrosion behavior of Ti-6Al-4V alloy, a prevalent orthopedic material. The study investigates the impact of alternative electrical signals at different frequencies on the alloy’s electrochemical behavior in a simulated body environment. The human body always has natural sinusoidal potential due to, e.g., heart palpitations and brain/nervous system activities. Ignoring such natural activities may lead to underestimating the corrosion performance of the Ti-6Al-4V alloy in the body. By analyzing anodic and cathodic responses and the net faradaic current induced by alternating current potential, the research sheds light on the influence of electrical fields on corrosion rates. Understanding these dynamics could lead to improved implant materials, mitigating corrosion-related challenges and enhancing implant performance over the long term. Results of this work indicated that frequent oxidation and reduction at certain frequencies may induce corrosion and hinder biomimetic apatite formation, impacting osseointegration. Natural alternative currents in the body affect the corrosion performance of Ti-based implant alloys, highlighting the need for consideration in biomedical applications. Full article

With escalating global regulatory pressure for countries to adhere to emission laws, repurposing existing natural gas pipelines for hydrogen-based commodities stands to be an economical solution. However, the effects of hydrogen embrittlement must be thoroughly considered for this application to avoid the unexpected catastrophic failure of these pipelines. The literature proposes several physicochemical embrittlement models. This paper reports one aspect of hydrogen embrittlement that remains to be quantified: the recovery of ductility (embrittlement) of mild steel specimens subjected to artificially accelerated hydrogen absorption via electrochemical charging as a function of time. The effects of charging duration and particularly the delay period between charging and mechanical tensile testing were investigated. Unsurprisingly, longer charging time shows a greater loss of elongation; however, a more extensive recovery of ductility correlated with longer charging time in the first few days after charging. The data also show that while the uncharged mild steel met all minimum required values for strength and elongation for the specified grade, there was a substantial variability in the elongation to failure. The same trends in variability of elongation translated to the hydrogen-charged specimens. Due to this extensive variability, failure to meet the elongation specification of the grade is reported based on the worst-case scenario obtained for a given set of samples for each exposure condition. These results have practical implications for the monitoring and testing of infrastructure exposed to hydrogen, particularly as this relates to industry planned operational shutdown schedules. Full article

An impedance model based on the Volmer–Heyrovsky–Tafel mechanism was developed to study the kinetics of the hydrogen evolution reaction on polycrystalline gold electrodes at moderate overpotentials in aqueous H₂SO₄ (0.5 and 1.0 M) solutions. The model was optimized on data from potentiodynamic polarization and electrochemical impedance spectroscopy, and model parameters were extracted. Consistent with expectations, the magnitude of the impedance data indicated a higher rate of hydrogen evolution at lower pH. Also, the fractional surface coverage of adsorbed hydrogen (${\theta }_{Hads}$) increases with increasing overpotential but the small value of ${\theta }_{Hads}$ indicates only weak adsorption of H on gold. Tafel slopes and exchange current densities were estimated to be in the range of 81–124 mV/dec, and 10⁻⁶ and 10⁻⁵ A/cm² in H₂SO₄ (0.5 and 1.0 M), respectively. The results show that the model accounts well for the experimental data, such as the steady-state current density. Sensitivity analysis reveals that the electrochemical parameters (${\alpha }_1, {\alpha }_2, k_1^0, k_{-1}^0, {\mathrm{a}\mathrm{n}\mathrm{d} k}_2^0)$ associated with the kinetics of the hydrogen evolution reaction have a major impact on the calculated impedance but the standard rate constant for hydrogen oxidation reaction ($k_{-2}^0)$ does not strongly affect the calculated impedance. Full article

Corrosion inhibitors are one of the best practices to prevent the far-reaching negative impacts of corrosion on ferrous alloys. A thorough understanding of their corrosion-inhibiting effects is essential for a sustainable economy and environment. Anionic surfactants are known to act efficiently as corrosion inhibitors. Here, we present that in-situ atomic force microscopy (AFM) measurements can provide deep insights into the adsorption and inhibition mechanism of surfactants on stainless steel surfaces during local corrosion. These include the configuration of surfactant molecules on the surface and how the microstructure of the stainless steel surface influences the inhibition process. Three different anionic surfactants, namely palm kernel oil (PKO), linear alkylbenzene sulfonate (LAS), and fatty alcohol ether sulfate (FAES), were investigated on a titanium-stabilized ferritic stainless steel (1.4510) in NaCl solution. For PKO, the results show random adsorption of bi- and multilayer whereas LAS and FAES adsorb only as local corrosion occurs. Thereby, LAS accumulates only locally and especially at the titanium precipitates of the 1.4510 and FAES forms a densely packed monolayer on the surface. This leads to better corrosion inhibiting properties for LAS and FAES compared to PKO. Full article

Hydrogen embrittlement (HE) of steel pipelines in high-pressure gaseous environments is a potential threat to the pipeline integrity. The occurrence of gaseous HE is subjected to associative adsorption of hydrogen molecules (H₂) at specific “active sites”, such as grain boundaries and dislocations on the steel surface, to generate hydrogen atoms (H). Non-metallic inclusions are another type of metallurgical defect potentially serving as “active sites” to cause the dissociative adsorption of H₂. Al₂O₃ is a common inclusion contained in pipeline steels. In this work, the dissociative adsorption of hydrogen at the $\mathsf{\alpha }\text{-}{\mathrm{A}\mathrm{l}}_2{\mathrm{O}}_3\left(0001\right)/\mathsf{\alpha }\text{-}\mathrm{F}\mathrm{e}\left(111\right)$ interface on the $\mathrm{F}\mathrm{e}\left(01\overline{1}\right)$ plane was studied by density functional theory calculations. The impact of gas components of O₂ and CH₄ on the dissociative adsorption of hydrogen was determined. The occurrence of dissociative adsorption of hydrogen at the Al₂O₃ inclusion/Fe interface is favored under conditions relevant to pipeline operation. Thermodynamic feasibility was observed for Fe and O atoms, but not for Al atoms. H atoms can form more stable adsorption configurations on the Fe side of the interface, while it is less likely for H atoms to adsorb on the Al₂O₃ side. There is a greater tendency for the occurrence of dissociative adsorption of O₂ and CH₄ than of H₂, due to the more favorable energetics of the former. In particular, the dissociative adsorption of O₂ is preferential over that of CH₄. The Al-terminated interface exhibits a higher H binding energy compared to the O-terminated interface, indicating a preference for hydrogen accumulation at the Al-terminated interface. Full article

The disposal of high-level radioactive waste (HLW) and spent nuclear fuel (SF) presents a unique challenge for the prediction of the long-term performance of corrodible structures since HLW/SF containers are expected, in some cases, to have lifetimes of one million years or longer. Various empirical and deterministic models have been developed over the past 45 years for making predictions of long-term corrosion behaviour, including models for uniform and localised corrosion, environmentally assisted cracking, microbiologically influenced corrosion, and radiation-induced corrosion. More recently, fracture-mechanics-based approaches have been developed to account for joint mechanical–corrosion degradation modes. Regardless of whether empirical or deterministic models are used, it is essential to be able to demonstrate a thorough mechanistic understanding of the corrosion processes involved. In addition to process models focused on specific corrosion mechanisms, there is also a need for performance-assessment models as part of the overall demonstration of the safety of a deep geological repository. Performance-assessment models are discussed in Part 2 of this review. Full article