Corros. Mater. Degrad., Volume 3, Issue 2 (June 2022) – 8 articles

Hydrogen plays various roles in metals or at metal–environment interfaces. Well known effects on metals are hydrogen embrittlement, hydrogen enhanced local plasticity, hydrogen enhanced strain-induced vacancy, hydrogen accelerated oxidation, hydrogen-induced creep, and their synergy. In this study, the potential roles of hydrogen in materials degradation are demonstrated and studied by two different tests. One is the high temperature oxidation of Ni-based alloy in various environments with hydrogen penetration, and the other is the effects of neutron flux/fluence on the oxidation kinetics and SCC of 316L and 316LN stainless steels, regarding a possible role of transmuted H from N. The results emphasize that the hydrogen either permeated into metals from surrounding environments, such as high temperature water or gaseous hydrogen, or generated in metals by nuclei transmutation, such as hydrogen transmuted from N atoms in metals, which can promote metal oxidation through multiple mechanisms. Apparently, the oxidation/corrosion phenomenon is a synergy of sub-mechanisms. For instance, dissolved hydrogen (DH) is usually believed to slow down the corrosion process for lowering the open circuit potential (OCP). However, H also facilitates the transport of the cations in oxide, thereby accelerating the corrosion process. In this bi-mechanism system, two different, contradictory mechanisms work and exist simultaneously. Therefore, whether the metallic materials are benefited or degraded by the H during its oxidation process depends on which sub-mechanism is dominant. Namely, hydrogen can play the role an oxidant in the metal and metal/oxide interface to pre-oxidize metal elements, such as Cr, Ni, and Fe, and possibly promote inward oxygen diffusion and the oxidation rate at the interface. Moreover, hydrogen may play a role as a reductant in oxides where existing oxides can be reduced. Then, the protective capability of oxides will be decreased to result in corrosion acceleration at the metal–oxide interface. These phenomena were observed in Ni-based alloy and possibly austenitic stainless steel containing N such as 316LN SS. This work demonstrates a part of the role of hydrogen on oxidation, and more extensive and systematic work is needed to delineate the role of hydrogen on oxidation with and without irradiation. Full article

Background: Evans’s drop is a classic corrosion experiment that is nearly 100 years old, and it is analogous to other corrosion systems promoted by O₂ gradients. The availability of more robust finite element software packages opens the possibility to reach a deeper understanding of these kind of corrosion systems. Methodology: In order to solve the problem, the model includes the governing mass transport diffusion and migration equation and the material balance in a nonsteady state by the finite element method. This is performed using COMSOL Multiphysics to predict the tertiary current and potential distribution considering the geometry, reaction kinetics, and mass transport for each ionic species. Significant Findings: A simulation of the tertiary current and potential distribution of the Evans’s drop corrosion experiment on an iron surface is presented. An oxygen concentration difference of 0.18 mol m⁻³ between the center and the drop periphery sets up a potential difference of 60 mV which acts as a corrosion driving force. Reaction kinetics are described by Tafel equations. Results include the evolution of concentration profiles for OH⁻, Fe²⁺, Fe³⁺, Fe(OH)₂, and Fe(OH)₃. Full article

The majority of works in the field of chloride-indued corrosion of steel in concrete are focused on the cracks formed by the corrosion products. However, the number of studies on the influence of cracks (pre-cracked concrete) on corrosion is limited. Cracks create preferential/free paths for the penetration of chlorides, water, and oxygen into concrete; thus, the presence of cracks in concrete can intensify chloride-induced corrosion of steel reinforcement. This paper presents a review of the effects of cracking on the corrosion of steel in concrete. It was widely reported in the reviewed papers that cracks have a negative impact on concrete durability. They influence the chloride penetration and the chloride-induced corrosion of reinforcement in terms of the initiation and propagation stages. This influence is a complex function of many factors, including mix design, exposure conditions, crack frequency, crack orientation, crack width, and cover depth. Although there is a general agreement on the effects of cracks on the initiation of corrosion, the role of cracks and their widths on the propagation of corrosion in the long term is still under debate. Full article

This work presents results allowing an unequivocal correlation of the observations of strong nonlinear elastic features of ultrasonic waves (values of the nonlinearity parameters exceeding the thresholds corresponding to undamaged states), with the critical events of the corrosion-induced surface cracking of reinforced cement-mortar specimens. These observations point to the possibility of the early detection of cracking using nonlinear ultrasonic (NLU) techniques. Experimental evidence is presented on the existence of active net mass transport processes, due to wick action, in the course of the corrosion tests, in the experimental conditions of this work. These phenomena might explain the observed abrupt shifting of the nonlinear parameter values (typically increasing and then decreasing post-peak, even reaching values typical of the undamaged state), and, partially, the high variability obtained for the values of the nonlinear parameters in damaged (cracked) states. Finally, some consequences are derived from the point of view of use of the NLU techniques in engineering practice, i.e., in surveys aimed at evaluating reinforced concrete structures affected by corrosion. Full article

Even though it is a noble metal, silver will corrode in ambient atmospheres, predominantly by reacting with sulfur-containing gases such as hydrogen sulfide (H₂S) and carbonyl sulfide (OCS) to form the silver sulfide (Ag₂S) acanthite. Other aspects of the environment, such as relative humidity and the presence of oxidizing species, also play a critical role. With the emergence of silver nanoparticles for a range of technological and medical applications, there has been a revival of interest in the corrosion behavior of this important metal. This article reviews the current understanding of the atmospheric corrosion of silver in both the bulk and nanoparticle forms. Gaps in our current understanding and areas for future investigation are identified. Full article

Among the leading consequences of corrosion in reinforced concrete structures (RCS) the cross section reduction in steel bars should be mentioned, coupled to a decay of their mechanical material properties. This paper recalls the main literature findings on the topic and describes a wide collected database of experimental tensile tests performed on naturally corroded reinforcements. The principal predictive degradation laws available in the scientific literature to assess the residual mechanical properties of the corroded reinforcements are synthesized. A first attempt to evaluate the reliability of the literature decay laws to simulate the mechanical performance of naturally corroded steel reinforcement subjected to both uniform and pitting corrosion is performed. Finally, some remarks are suggested on both the tested naturally corroded steel reinforcement and the available degradation laws. Full article

Recycled aggregate produced from crushed waste concrete is suitable for use in structural concrete. It reduces the demand for non-renewable resources and also for energy in general. However, RA is more porous than most natural aggregates. The porosity of the concrete cover defines the corrosion resistance of reinforced concrete, and it is therefore disputed how the use of recycled aggregate may affect the durability of reinforced concrete. This paper describes the corrosion-related performance of reinforced concrete with recycled aggregates in the initiation stage (determined by the carbonation and chloride ingress) and propagation stage (determined by the electrical resistivity and cracking) of corrosion. The aspects of interest are not only the porosity of RA but also its effects on the chloride binding, carbonation, electrochemical properties and corrosion cracking development. Full article

Low-alloy reactor pressure vessel steels have a rather low susceptibility to stress corrosion cracking (SCC) in a boiling water reactor (BWR) environment if the high-temperature water contains no anionic impurities. Recent investigations revealed that under oxidizing BWR normal water chemistry (NWC) conditions extremely small amounts of chloride, can cause very high SCC growth rates in these materials. Therefore, the effect of continuous and temporary chloride additions on the crack initiation behaviour was explored by a series of constant extension rate tensile (CERT) and constant load tests in high-temperature water. In an NWC environment, containing ≥2 ppb of chloride, strain-induced corrosion cracking (SICC) initiation occurred briefly after the onset of plastic yielding and at much smaller strains than in high-purity water. On the other hand, under reducing hydrogen water chemistry conditions with up to 700 ppb chloride, no SICC was detected up to very high strains. CERT experiments, with moderate short-term chloride transients before and during the loading, showed that even serious mechanical loading transients, one day after returning to high-purity water, did not result in early SICC initiation. Full article