Corros. Mater. Degrad., Volume 6, Issue 1 (March 2025) – 13 articles

The hydrolytic stability of thin poly(ethyl 2-cyanoacrylate), PECA, adhesive films on grit-blasted mild steel substrates was investigated using electrochemical impedance spectroscopy (EIS). Using this novel approach for such adhesive films, the effects of two additives, salicylic acid (SA) and phthalic anhydride (PA), were studied, specifically measuring their influence on polymer film/surface impedance and capacitance changes over a period of 14 days. Results indicate that SA decreased the polymer film hydrolytic stability rapidly, resulting in a substantial drop in impedance modulus from ~10 kΩcm² to ~10 Ωcm² at 100 Hz due to electrolyte ingress, whilst the PA-containing film modulus also diminished from ~4 MΩcm² to ~1 kΩcm² at 100 Hz. Furthermore, the capacitance values of the SA-containing films rose (up to ~100 µFcm⁻²), demonstrating the onset of a charge transfer (corrosion) process within the first 12 h exposure to a saline electrolyte. In contrast, the PA-containing film’s transition from a film-dominated capacitance (~0.01 µFcm⁻²) to a larger double-layer capacitance took (~1 µFcm⁻²) took several days and was accounted for by differences in the additive’s chemistry, demonstrating the ability of EIS to detect changes in both bulk film (e.g., moisture ingress and bond scission) and metal-film interfacial processes (e.g., onset of corrosion) in real time. Comparison was also made with a standard industry combined tensile test/hydrolytic accelerated ageing regime. Unlike, EIS this did not, however, give useful time-dependent information, although after 6 weeks a decrease in bond strength occurred in the order PA-containing film < PECA< SA-containing film in agreement with the EIS results, thus demonstrating the effectiveness of EIS for monitoring the degradation of such thin film adhesives. Full article

In this work, the microstructure and degradation properties of a novel metal matrix composite composed of Mg with the addition of 1 vol. % hydroxyapatite nanopowder (Mg + 1 vol % nHAp) were evaluated. The composites in the form of discs produced using spark plasma sintering (SPS) were subjected to plastic deformation using a modified extrusion technique with an oscillating die located at the end of the extruder (called KoBo), which enables deformation without the preheating of the initial billet. The microstructure was analyzed using optical and scanning electron microscopy (SEM) with subsequent electron backscattered diffraction (EBSD) measurements. The corrosion properties were evaluated based on electrochemical and immersion tests. To assess early biological performance, cytotoxicity tests were performed. The addition of nHAp did not significantly change the corrosion rate; however, the subsequent plastic deformation greatly decreased it. Interestingly, the sample after plastic deformation without the preheating of the initial billet was characterized by the highest cell viability. Overall, the addition of nHAp improved the biological assessment of the extruded composite; however, during plastic deformation, due to the refinement of loosely adherent nHAp and the formation of bimodally distributed grain sizes, a high number of microgalvanic couples were formed, resulting in worse corrosion performance. Full article

Coastal reinforced concrete (RC) bridge piers are often subjected to seawater splash and tidal action, leading to bottom corrosion of the steel reinforcement and thereby producing the corrosion–induced cracks of concrete. The increased risk of vehicle collisions to piers poses significant threats to bridge and traffic disruption, potentially causing severe pier damage or even bridge collapse. Many studies have investigated the dynamic responses of bridge piers to vehicle collisions, but no study of the effect of the corrosion degradation of piers on vehicle collision response and damage has been reported yet. This study numerically investigates the influence of bottom chloride-induced corrosion on the truck collision response and damage of coastal RC bridge piers by using LS-DYNA. The results reveal that localized damage occurs in the impact zone for both intact and corroded piers. For the corroded pier, punching shear failure becomes the dominant failure mode and the pier is more vulnerable to collapse at lower truck velocities. Corrosion degradation influences the dynamic response, increasing the lateral displacement of the pier while reducing the impact force, particularly during the engine and cargo impact stages of truck collisions. The impulses in 500 ms collision time show reductions of 1.1% and 4.3% for piers with 45-year and 90-year corrosion, respectively. Notably, the lateral displacement at the bottom corrosion zone shows no oscillations due to the punching shear failure. Full article

Etching methods of aluminum foils used in electrolytic capacitors are selected based on the operating voltages, with DC and AC etching typically used for the anode foils of high- and low-voltage capacitors, respectively. The initial pits continue to grow and eventually form tunnels or cubic pits by DC or AC etching, respectively. This paper describes the pit formation and growth process, focusing on the involvement of passive film inside the pit and facet dissolution. In particular, it is found that high-purity aluminum foil containing Ti promotes the formation of passive film (etch film) inside pits during the cathodic half cycle of AC etching, and Cu promotes facet dissolution. These behaviors significantly affect the surface area expansion by electrolytic etching. In addition, the effects of crystal orientation, surface defects associated with oxide film crystallization, and a trace element, Pb, as factors affecting the pit initiation sites will be discussed. Full article

Research on bone regeneration has always been an intense and challenging field of tissue engineering. Biodegradable metals represent a novel class of biomaterials combining superior mechanical qualities with a capacity to promote bone growth. Among them, magnesium (Mg) and its alloys have been proposed as innovative biomaterials for bone grafting therapy due to their non-toxic nature and comparable mechanical properties to bones. In addition, they are lightweight, biocompatible and biodegradable. They offer several advantages over other implant metals, including reduced stress-shielding effects and unnecessity for a second surgery to remove them. Unfortunately, their clinical application is limited due to the rapid degradation rates in rather aggressive physiological conditions. Therefore, the development of Mg-based implants possessing a controlled degradation in accordance with the kinetics of bone healing is necessary. On the other hand, protective yet biocompatible and biodegradable surface coatings have emerged as a useful strategy to fulfill the diverse clinical requirements, including effective corrosion resistance. Calcium orthophosphates (abbreviated as CaPO₄) are excellent candidates for producing such coatings as they are well tolerated by living organisms. However, due to its high chemical reactivity and a low melting point, Mg-based grafts require specific parameters for successful CaPO₄ deposition. This paper reviews currently available preparation methods of CaPO₄ deposits on Mg and its alloys, aiming to build up a comprehensive knowledge framework of deposition techniques, processing parameters, performance measures in terms of corrosion resistance, adhesion strength and biocompatibility. The literature analysis shows that CaPO₄ protective coatings increase the ability of magnesium-based metallic biomaterials to withstand corrosion and improve the biocompatibility of their surfaces in all cases. Full article

In most countries, low- and intermediate-level wastes (LILWs) are cemented in carbon steel drums for later disposal. The durability of waste packages is determined by the chemical environment generated by both cement-based engineered barrier systems and the aggressive species present in the waste. Decontamination sludges are challenging wastes that are currently not accepted for final disposal due to their acidic nature and high concentrations of organic species and complexants. Thus, it was proposed to use electrochemical measurements to study the corrosion of steel sheets, simulating drums embedded in new alkali-activated slag (AAS) formulations with surrogate decontamination liquids, and determine their viability for use as confining matrices in order to increase the service life of the drums. The carbon steel coupon embedded in the Portland cement reference (R-L) paste showed the best corrosion resistance, followed by that of steel embedded in sodium silicate-activated slag (BFS-S-L) paste. This behaviour may be related to an improvement in the protective nature of the surface film. However, in sodium carbonate-activated slag (BFS-C-L) paste, the effect of the sludge in the matrix seemed to be more intense, leading to a pH decrease in the paste porewater, an effect that could hinder the formation of a passive layer on the surface of the carbon steel. Under such conditions, the initiation of the corrosion process seems to be favoured, resulting in the formation of a non-protective scale consisting mainly of hematite. Full article

Carbon steel structures employed to convey hydrocarbons and other dangerous fluids, such as oil or flammable liquids, are equipped with degradation prevention systems, which typically consist of a cathodic protection (CP) system combined with an external insulating coating, both designed to reduce the corrosion rate below 10 µm/year. The presence of electrical interference, both AC and DC, can cause significant corrosion damage to metallic structures, even when CP is applied. DC interference is determined by the presence of a third-party CP system or public transportation system. AC interference may occur through conduction or induction mechanisms, caused by high-voltage powerlines or high-speed trains, powered by AC. Both interferences may lead to localized corrosion at coating defects, despite compliance with the −0.850 V saturated Cu/CuSO₄ reference electrode (CSE) protection criterion. Considering AC-induced corrosion, both field failures and laboratory investigations have demonstrated that corrosion can occur at industrial frequencies, and when CP is applied following the standards. Even though AC-induced degradation is generally not as severe as DC interference, uncertainties remain regarding the protection potential range necessary to achieve acceptable corrosion prevention under AC interference. To formulate a CP criterion under AC interference, weight loss measurements were conducted on carbon steel samples under cathodic protection in solutions that simulate real soil conditions. Carbon steel coupons protected by CP were interfered with AC densities ranging from 1 A/m² to 800 A/m² for four months. During this time interval, polarization potential, protection current density and AC density were monitored. Based on the experimental data gathered during this study, a proposal for a risk map is also suggested. The results indicate that overprotection (potentials < −1.2 V CSE) represents the most dangerous scenario when AC interference is involved. Full article

In the current study, the authors have listed the causes of common failures in hydro turbine blades. In the following, coatings, as one of the practical solutions that can be utilized in the hydropower industry, were selected for further investigation. In this regard, nanocoating technology is used to prevent the above-mentioned failures, as well as to extend the service lifetime of turbine blades, to increase the inspection time, i.e., the overhaul intervals, and to reduce repair costs. Therefore, firstly, the raw materials of runner blades in different types of turbines were checked. The collected data revealed that this equipment is usually made of stainless steel (i.e., 304 and 316L). Therefore, the main focus of the current research was a general investigation of the effects of different nanocoatings on the material properties, including the wear, corrosion, and erosion, of 304 and 316L steels. Finally, a coating process used in this industry that is suitable for overhaul rather than initial construction was investigated. The advantages of using nanocoatings compared to traditional coatings in this industry were enumerated. In addition, the effects of single-layer and multi-layer coatings with different compositions on the corrosion, wear, and erosion properties of each of these stainless steels were discussed. Eventually, considering the gaps in past research and summarizing the collected results, a future research direction was proposed, including different combinations of materials to create new nanocoatings (with different percentages of nano alumina and titanium carbide). Full article

Chemical Equilibrium Fracture Mechanics (CEFM) studies the effect of chemical reactions and phase transformations on crack-tip fields and material fracture toughness under chemical equilibrium. An important CEFM direction is hydrogen-induced embrittlement of alloys, due to several industrial applications, including those within the industrial value chain of hydrogen that is under development, which, according to European and international policies, are expected to contribute significantly to the replacement of fossil fuels by renewable energy sources. In the present study, the effect of hydrogen on the crack-tip fields of hydride- and non-hydride-forming alloys is examined. The crack-tip stress and hydrogen concentration distributions are derived under hydrogen chemical equilibrium, which is approached by considering the coupling of the operating physical mechanisms. In all cases, analytic relations are derived, thus facilitating integrity assessments, i.e., without the need to rely on complicated numerical methods, expected to lead to the development of respective tools in industrial applications. It is shown that, in the case of hydride precipitation, there are significant deviations from the K, HRR, and Prandtl fields, and, thus, the well-known approaches of Linear Elastic Fracture Mechanics (LEFM) and Elastic–Plastic Fracture Mechanics (EPFM) need to be accordingly modified/extended. Full article

Biomedical alloys in general, except for the biodegradable type, exhibit passive behavior in neutral chloride solutions. Two commonly used biomedical alloys are nitinol (NiTi) and Co-35Ni-20Cr-10Mo (CoNiCrMo). In this work, the passive behavior of electropolished NiTi and CoNiCrMo in a simulated physiological solution (phosphate-buffered saline) was compared using data largely obtained from our previous studies involving potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The potentiodynamic results showed a marked difference in passive behavior between the alloys, with NiTi remaining completely passive up to the oxidation of water and CoNiCrMo, in contrast, undergoing solid-state oxidation and then transpassive dissolution. Both alloys exhibited Tafel-type behavior over the initial part of the passive range. A small but distinct difference in the apparent Tafel slopes was found between the two alloys and can be attributed to the difference in their predominant oxide; that is, TiO₂ versus Cr₂O₃. The EIS results also showed marked differences between the alloys in terms of the oxide thickness and resistivity. The thickness was greater for NiTi—consistent with surface analytical results—and differed in potential dependence between the two alloys in the passive region. The oxide resistivity, conversely, was substantially lower for NiTi and showed a similar potential dependence for the two alloys. Full article

Corrosion is one of the causes of failure in reinforced concrete structures, and forming a passive film on the steel is essential for protection. Although several studies have looked at passive film formation in concrete pore solutions, few have considered its formation in hardened concrete and the influence of silica fume (SF) in the binder composition. This study aims to evaluate the influence of the SF content on passive film formation time in concrete. Periodic measurements assessed the electrical resistivity and corrosion current density of concrete samples containing 5%, 10%, 15%, and 20% SF. The alkalinity of the mixtures and the kinetics of the pozzolanic reaction were also monitored by XRD and titration tests. The control mixtures exhibited susceptibility to corrosion, regardless of the curing age evaluated. In contrast, the partial replacement of cement with SF accelerated the formation of the passive film on the steel surface, suggesting a delayed onset of corrosion due to modifications in the physical properties of the concrete. Also, the portlandite content and pH can predict passive film formation, with SF significantly accelerating this process. Full article

Corrosion investigations of steel-reinforced concrete structures are often based on half-cell potential measurements, in which the diffusion potentials can be a significant source of measurement errors. Therefore, the diffusion potentials must be taken into account in order to enable accurate half-cell potential measurements. This study covers the measurement of the diffusion potentials in cement mortars with pH differences due to carbonation and various mortar moisture conditions. The effect of chloride exposure of the mortars on the diffusion potentials is outside of the scope of this study. The mortars consisted of ordinary Portland cement (OPC) and blast furnace cement (BFC) with water–cement ratios of 0.5–0.7. The use of color indicators allows for the observation of the pH drop around the carbonation front, which propagates as the carbonation progresses. The diffusion potentials in the mortars under study have measurement values between 10 and 240 mV. The measured diffusion potentials seem to correlate with the magnitude of the pH drop rather than the progress of the carbonation depth. The moisture condition of the mortars significantly affects the magnitude of the arising diffusion potentials. Full article

Seawater ballast tanks in vessels are subject to severe service conditions caused by repeated filling/emptying, as well as temperature variation. Consequently, relatively thick, barrier-type coatings are used for corrosion protection of their internals. These are generally formulated with solvent-based epoxy binders and contain a range of flake pigments designed to limit environmental entry. Here, we report on a detailed study of damage processes in order to understand the mechanisms of failure after hygro-thermal cyclic corrosion testing. Similar formulations were cured using variant phenalkamine cross-linkers. Visual observation after corrosion testing shows minimal changes and no sign of corrosion damage. However, high-resolution analytical microscopy and nanoscale tomography reveal the onset of microstructural and chemical damage processes inside the coating. Thus, kaolin and talc pigments in the coating remained stable under hygro-thermal cycling; however, dolomite and barium sulphate dissolved slightly, causing voids. Galvanic protection of the substrate by aluminium flake pigments was disproven as no electrical connection was evident. Vibrational spectroscopy revealed a decrease in residual epoxy functionality after exposure for the coating cured with the more stable phenalkamine. This was correlated with an increase in glass transition temperature (Tg) and no observable corrosion of aluminium flakes. In contrast, the less stable phenalkamine cross-linker caused the binder Tg to decrease and aluminium flakes and substrate corrosion to become evident. Full article