Aqueous Corrosion Research Articles

Effect of Heat Treatment on Microstructure and Aqueous Corrosion Properties of AlCoCrNiFe High Entropy Alloy

Effect of Heat Treatment on Microstructure and Aqueous Corrosion Properties of AlCoCrNiFe High Entropy Alloy

Revealing the Reaction Pathway of Anodic Hydrogen Evolution at Magnesium Surfaces in Aqueous Electrolytes.

Aqueous metal corrosion is a major economic concern in modern society. A phenomenon that has puzzled generations of scientists in this field is the so-called anomalous hydrogen evolution: the violent dissolution of magnesium under electron-deficient (anodic) conditions, accompanied by strong hydrogen evolution and a key mechanism hampering Mg technology. Experimental studies have indicated the presence of univalent Mg+ in solution, but these findings have been largely ignored because they defy our common chemical understanding and evaded direct experimental observation. Using recent advances in the ab initio description of solid-liquid electrochemical interfaces under controlled potential conditions, we describe the full reaction path of Mg atom dissolution from a kinked Mg surface under anodic conditions. Our study reveals the formation of a solvated [Mg2+(OH)-]+ ion complex, challenging the conventional assumption of Mg2+ ion formation. This insight provides an intuitive explanation for the postulated presence of (Coulombically) univalent Mg+ ions, and the absence of protective oxide/hydroxide layers normally formed under anodic/oxidizing conditions. The discovery of this unexpected and unconventional reaction mechanism is crucial for identifying new strategies for corrosion prevention and can be transferred to other metals.

Effect of Tempering Temperature on the Aqueous Corrosion Resistance of 9Cr Series Heat-Resistant Steel

In this investigation, the aqueous corrosion resistance of 9Cr series heat-resistant steel during tempering was investigated. Optical Microscopy (OM), Scanning Electron Microscopy (SEM), and Energy Dispersive Spectrometer (EDS) were used to analyze the effect of tempering temperature on the microstructure and precipitation behavior of precipitates. The heat-resisting steel was heated to 1150 °C for 1 h, and then tempered at different temperatures between 680 °C and 760 °C for 2 h. The microstructure of the heat-resistant steel after tempering was composed of lath-tempered martensite and fine precipitates. The hardness decreased with increasing tempering temperature, ranging from HBW 261 to HBW 193. The aqueous corrosion resistance improved as the tempering temperatures increased from 680 °C to 720 °C but deteriorated at higher temperatures, such as 760 °C, which was obtained by an electrochemical corrosion performance test. The aqueous corrosion resistance was affected by the decrease in dislocation density and the decrease in Cr solution in the tempered martensite. With the increase in the tempering temperature, the aqueous corrosion potential first increases and then decreases, the self-corrosion current density first decreases and then increases, and the polarization resistance first increases and then decreases. Furthermore, the increase in corrosion resistance is attributed to the reduction in dislocation density and chromium depletion in the martensitic structure as the tempering temperature approaches 720 °C. This paper reveals the effect of tempering temperature on the corrosion resistance of 9Cr series heat-resistant steel, which is a further exploration of a known phenomenon.

Uncovering the electrochemical stability and corrosion reaction pathway of Mg (0001) surface: Insight from first-principles calculation

An understanding of the anomalously enhanced hydrogen evolution reaction (HER) of magnesium (Mg) under anodic polarisation in aqueous corrosion is paramount for a predictive theory of its corrosion and metal electrocatalysis. Previous theoretical and experimental studies have proposed that sub-surface hydride phases play a role in this behaviour but the underlying atomic mechanisms remain unclear. By constructing theoretical surface Pourbaix diagrams, based on density functional theory (DFT) calculations, we have identified the atomic structure of a sub-surface hydride phase on the Mg (0001) surface that remains electrochemically stable under significant anodic overpotentials across a wide pH range. Specifically, this stability persists up to 0.38 VSHE under mildly alkaline conditions (e.g., pH = 8), thus providing thermodynamic support for the proposed hydride-enhanced HER under anodic conditions. Reaction barrier analysis establishes that the proposed sub-surface hydride phase could promote anodic HER via a Heyrovsky pathway, based on hydrogen outward diffusion, with an energy barrier of 1.54 eV as the rate-limiting step, showing an anodic characteristic and significantly favouring external anodic polarisation. Furthermore, we have established that the surface adsorption condition, contingent on both the pH and potential, significantly influences the mechanism and kinetics of the initial corrosion of Mg.

Thermodynamic evaluation of the aerial and aqueous oxidation of Al – Mg, Al – Si and Al – Mg – Si system alloys at 298 K

Aluminum and magnesium are the lightest structural metals, and therefore, various alloys based on them are widely used in both, automotive and aerospace industries. However, aluminum and magnesium are very easily affected by atmospheric and aqueous corrosion, and, therefore, the alloying elements should enhance their corrosion stability. In this work, the thermodynamic analysis of phase and chemical equilibria involving aluminum and magnesium alloys doped with silicon in oxygen–containing air environments, as well as the analysis of chemical and electrochemical equilibria involving these alloys in aqueous environments is conducted. The phase and chemical equiliibria in the Al–Mg, Al–Si, Mg–Si, and Al–Mg–Si systems at 298 K are considered, and the thermodynamic activities of the components of common Al–Mg–Si system alloys are calculated. The invariant chemical equilibria in the systems Al–Mg–O, Al–Si–O, Mg–Si–O at 298 K are considered, the isothermal section of the state diagrams of these systems are plotted, and the oxidation scheme of the Al–Mg–Si system alloys in excess oxygen is proposed. The chemical and electrochemical equilibria in the Al–Mg–Si–H2O system at 298 K are considered and presented in form of the activity – pH and the potential – pH diagrams, and the oxidation of the Al–Mg–Si system alloys in aqueous environments is discussed.

High-temperature aqueous corrosion of MO–Na2O–B2O3–SiO2 glass and glass-ceramic coatings on metallic substrates: Effect of alkaline earth metals M2+= {Ca2+, Sr2+, Ba2+}

This investigation aims to assess the impact of 2 A alkaline-earth oxides on the alteration of glass/glass-ceramic coatings on steel under conditions of exposure to hot water. Experiments involved integrating CaO, SrO, and BaO into sodium-borosilicate glass systems after that a melting-quenching process to obtain frits. Coated and sinter-crystallized samples denoted as GC-Ca, GC-Sr, and GCC-Ba were exposed to hot aqueous corrosion according to DIN 4753–3 at 95 °C, which determined weight loss after 42 days. ICP-MS analyzed aqueous solutions for element leaching. Results indicated that glass-ceramic coatings (GCC-Ba) outperformed glass coating(GC-Ca, GC-Sr). GCC-Ba demonstrated enhanced stability, attributed to limited ion exchange and diffusion at high temperatures, enhancing corrosion resistance, supported by sanbornite crystal phase presence. Total element release by ICP-MS and 42 days of hot water corrosion coatings' weight loss after 42-day corrosion test lined up: GC-Sr > GC-Ca > GCC-Ba.

Performance of a Ship-Based Cupronickel Alloy in Exposure Conditions of Arabian Seawater-A Comparative Study.

Cupronickel-based alloys are widely known for their excellent resistance against aqueous corrosion, however, they can be susceptible to corrosion at accelerated rates and premature failure when exposed to a polluted or brackish seawater medium, even for short-term exposure durations. This unfamiliar corrosion behavior may be a result of the formation of an unprotected corrosion film during the early exposure durations. The paper investigates the corrosion phenomenon in cupronickel 90/10 alloy, by exposing the coupons in two different seawater compositions in the Arabian Sea region. Corrosion losses were investigated on the experimental coupons in a submerged position, for a maximum exposure duration of 150 days, using the conventional weight loss method and a new dimensional metrology-based measurement technique. Additionally, in this research the tubes of a marine heat exchanger having similar material that failed prematurely during operation in the Arabian Sea were also investigated for corrosion losses, followed by the characterization of the corrosion deposits using following analytical techniques: SEM, EDS, XRD and Raman Scattering. The experimental results showed significantly higher corrosion losses on coupons exposed to seawater site rich in pollutants and nutrients including dissolved inorganic nitrogenous compounds, compared to those subjected to a natural seawater solution in corrosion tanks maintained in a controlled environment.

Effect of formic acid on aqueous corrosion mechanisms of mild steel

The effect of formic acid (HCOOH or shortly HFr) on corrosion mechanisms of X65 steel was systematically investigated in pH controlled, N2-sparged and CO2-sparged solutions using potentiodynamic polarization and linear polarization resistance (LPR) techniques. The results from the electrochemical experiments conducted in 1 wt.% NaCl solutions at 1 bar (total pressure) confirm that HFr is not significantly electroactive and therefore is not directly reduced on the steel surface under the conditions studied here. Experiments at various HFr concentration, temperature, pH, and flow rate also confirm that the main role of HFr on the corrosion of X65 steel is through the “buffering effect” mechanism. According to this mechanism, weak acids such as HFr increase the cathodic limiting current by providing hydrogen ions (H+) through their chemical dissociation similarly as is seen with acetic acid (CH3COOH or HAc).A comparison between HFr and HAc shows that these two organic acids have some differences in their behavior. First, HAc seems to retard the anodic reaction and decrease the corrosion rate, especially at lower temperatures and higher concentrations, while HFr does not. Second, the influence of these two acids on increasing the limiting current density seems to be similar at 30 °C, but at higher temperatures (50 °C, 80 °C), the cathodic limiting current density in the presence of HAc is greater than that with HFr at the same molar concentration. Under similar experimental conditions, HAc was observed to be less corrosive at lower temperature (30 °C), and more corrosive at higher temperatures (50 °C and 80 °C) compared to HFr at the same molar concentration.Experimental data collected in this study were used to validate a newly developed mechanistic model. According to our investigations this model shows an accurate fit to the experimental data at different HFr concentrations and pH at 30 °C. However, the model deviates from the experimental limiting current density value at higher temperatures (50 °C and 80 °C). It is speculated that this deviation results from a potential inaccuracy in the available temperature function for equilibrium constant of HFr dissociation reaction, which requires further investigations.

Effect of precipitated Mg-containing corrosion products on the anodic behavior of steel in aqueous corrosion for Zn-Al-Mg coated steel

The role of precipitated Mg-containing corrosion product in the anodic behavior of the steel in aqueous corrosion was ascertained to analyze the corrosion protection mechanism at steel substrate of the Zn-Al-Mg coated steel. For the Zn-Al-Mg coating, the corrosion products that formed during the immersion test passivated the steel in the deaerated solution at pH 8.2. EDS analysis revealed that Mg-species remained on the steel after polarization. However, the concentration of Mg decreased after polarization. The results indicated that the alkalization and barrier effect by the Mg-containing corrosion products passivated the steel substrate, preventing red rust generation at the cut-edge.

Tuning chemical short-range order for stainless behavior at reduced chromium concentrations in multi-principal element alloys

Single-phase multi-principal element alloys hold promise for improved mechanical properties as a result of multiple operative deformation modes. However, the use of many of these alloys in structural applications is limited as a consequence of their poor aqueous corrosion resistance. Here we introduce a new approach for significantly improving the passivation behavior of alloys by tuning the chemical short-range order parameter. We show that the addition of only 0.03 to 0.06 mole fraction of Al to a (FeCoNi)0.9Cr0.1 alloy changed both the magnitude and sign of the Cr-Cr order parameter resulting in passivation behavior similar to 304L stainless steel containing twice the amount of Cr. Our analysis is based on comparing electrochemical measures of the kinetics of passive film formation with chemical short-range order characterizations using time-of-flight neutron scattering, cluster expansion methods, density functional theory and Monte Carlo techniques. Our findings are interpreted within the framework of a recently proposed percolation theory of passivation that examines how selective dissolution of the non-passivating alloy components and short-range order results in excellent passive films at reduced levels of the passivating component.

Leakage Quantification in Metallic Pipes under Different Corrosion Exposure Times

The combined effects of aqueous corrosion, stress factors, and seeded cracks on leakage in cast iron pipes have not been thoroughly examined due to the complexity and difficulty in predicting their interactions. This study seeks to address this gap by investigating the interdependencies between corrosion, stress, and cracks in cast iron pipes to optimise the material selection and design in corrosive environments. Leakage experiments were conducted under simulated localised corrosive conditions and internal pressure, revealing that leakage increased from 0 to 25 mL with crack sizes of 0.5 mm, 0.8 mm, 1 mm, and 1.2 mm, along with corrosion times of 0, 120, 160, and 200 h, and varying stress levels. An empirical model was developed using a curve-fitting approach to map the relationships among corrosion time, crack propagation, and leakage amount. The results demonstrate that the interaction between corrosion, stress, and crack propagation was complex and nonlinear, and the leakage amount increased from 0.7 to 0.10 mm every 15 min, as evidenced by SEM microstructure images and empirical data.

Augmentation of Polymer-FeCO3 Microlayers on Carbon Steel for Enhanced Corrosion Protection in Hydrodynamic CO2 Corrosion Environments.

Carbon dioxide (CO2) internal corrosion of carbon steel pipelines is a significant challenge and is typically managed by adding corrosion inhibitors. In certain operational conditions, a natural protective layer of iron carbonate (FeCO3) can form on the internal walls of the pipeline, offering inhibition efficiency comparable to that of standard surfactant inhibitors. However, incomplete coverage of the FeCO3 layer on carbon steel can sometimes trigger localized corrosion. Our previous research demonstrated that poly(allylamine hydrochloride) (PAH) can work synergistically with FeCO3 when the corrosion product partially covers X65 carbon steel surfaces in an aqueous CO2 corrosion environment. In this study, we utilize rotating cylinder electrode (RCE) tests along with electrochemical measurements to investigate the FeCO3-PAH hybrid structure in a dynamic environment. We characterize the general and localized corrosion behavior as well as the surface properties of both naturally formed FeCO3 and FeCO3-PAH hybrid layers using interferometry and focused ion beam scanning electron microscopy.

Numerical exploration of a fully mechanistic mathematical model of aqueous CO2 corrosion in steel pipelines

A numerical exploration of a comprehensive mechanistic aqueous carbon dioxide (CO2) corrosion model is conducted across a range of temperatures (273–313 K), CO2 partial pressures (0.1–1 bar), and bulk pHs (5–6.5). Contour plots are produced to examine the impact on corrosion rate, surface pH, and surface saturation index of iron carbonate (FeCO3). Two response patterns are identified depending upon the limiting behaviour of the system, with a transition from charge-transfer control to mass-transport control as temperature is increased and partial pressure is reduced. FeCO3 surface saturation shows a strong correlation with the release of Fe2+ and increase in bulk pH.

An electrochemical study of iron carbonate layers formed on carbon steel during corrosion in elevated pressure CO2 environments

Iron carbonate (FeCO3) layers influence the electrochemical properties of carbon steel during aqueous corrosion in carbon dioxide–saturated environments. In this study, electrochemical measurements conducted in an autoclave at 80°C and 5 barg are combined with cross-sectional imaging to elucidate interfacial properties of X65 carbon steel at key stages of FeCO3 layer development. The effects of evolving system chemistry are also considered by variation of the X65 surface area to solution volume (A/V) ratio. FeCO3 reduces general corrosion rates through a combination of active site blocking and restriction of mass transport, with resultant layer properties dependent on the A/V ratio.

A comprehensive XPS investigation of the effect of aqueous corrosion on the surface of glass-zirconolite composite material (Fe–Al–BG–CaZrTi2O7)

Extensive X-ray photoelectron spectroscopy (XPS) analyses of iron–aluminum borosilicate glass (Fe–Al–BG), zirconolite (CaZrTi2O7), and Fe–Al–BG–CaZrTi2O7 composite material have demonstrated that a hydrated layer has been formed on the surface of these materials after exposure to water. The surface chemistry of Fe–Al–BG–CaZrTi2O7 composite material as a potential nuclear wasteform candidate was observed to change in a similar fashion to the borosilicate glass as a current wasteform material after these materials are exposed to water. The XPS measurements suggest that the aqueous corrosion of the Fe–Al–BG–CaZrTi2O7 composite material is a result of ion exchange, hydrolysis, and redox reactions of metal–oxygen bonds with water at the surface of the Fe–Al–BG–CaZrTi2O7 composite material. Moreover, the XPS results proved that the composition and chemical environment of the precipitated layer on the surface of the Fe–Al–BG–CaZrTi2O7 composite material after exposure to water remained unchanged between 270 and 365 days of exposure to water. The stability of the surface layer during this time frame could potentially protect the surface of the Fe–Al–BG–CaZrTi2O7 composite material from further corrosion.

Ab initio exploration of modified carbon nanotubes as potential corrosion inhibitors

In order to develop novel unexplored potential corrosion inhibitors, covalently modified single-walled carbon nanotubes (SWCNT) via benzoic (–PhCOOH) and aniline (–PhNH2) groups are being investigated as corrosion inhibitors for the first time. Utilizing a comprehensive approach, this study employed density functional theory (DFT), Monte Carlo (MC), and molecular dynamics simulations (MD) to assess the adsorption behavior of modified nanotubes as corrosion inhibitors on the Cu(111) surface within a simulated aqueous HCl corrosion medium. The results provided molecular information on the adsorption capability, geometry adsorption centers, and adsorption energies (Eads) of carbon nanotubes on the surface of Cu(111). The adsorption energy values unveiled robust interactions between SWCNT–PhCOOH and SWCNT–PhNH2 inhibitors and the Cu(111) surface, suggesting a highly effective corrosion protection mechanism. The calculated Eads values exhibited notable ranges, spanning from –260.82 to –308.18 kcal/mol for SWCNT–PhCOOH and –220.92 to –261.01 kcal/mol for SWCNT–PhNH2 with the maximum probability values, representing the most favorable adsorption scenarios, determined to be –292.96 and –229.39 kcal/mol, respectively. A key insight from Monte Carlo simulations underscored the inherent spontaneity of the adsorption process, corroborated by the consistently negative Eads values. These findings collectively underscore the substantial affinity of the inhibitors to the copper surface, contributing to a deeper comprehension of their corrosion inhibition capabilities.

Corrosion of 316L stainless steel in high temperature water and steam: Mechanisms of corrosion

316L stainless steel was exposed to 320 °C hydrogenated or aerated water and 480 °C steam for up to 72 h to determine the aqueous corrosion mechanisms. The thermodynamics of the corrosion process are interpreted using a new concept called the excess volume which predicts stable formation of pores in the inner oxide layer. Corrosion rates are found to be correlated with inner oxide porosity. Inner oxide thicknesses were measured, and thermodynamic modelling was used to determine that the rate-limiting step of corrosion is fluid transport of oxygen via pores in the inner oxide layer.

Investigation of Iron Dissolution Mechanism in Acidic Solutions with and without Dissolved CO2—Part I: Electrochemical Impedance Spectroscopy Measurements

Aqueous CO2 corrosion of mild steel is one of the major problems in the oil and gas industry. While current understanding primarily focuses on cathodic reaction mechanisms, less attention has been given to the impact of aqueous CO2 on the anodic iron dissolution reaction. In contrast, the mechanism of iron dissolution in strongly acidic environments has been thoroughly investigated. Among the reaction mechanisms found in the open literature, a multipath mechanism was identified that could explain the iron dissolution in strong acidic sulfate solution; both in terms of steady-state polarization sweeps and impedance data at various pH values and current densities. However, the role of aqueous CO2 in solutions containing chlorides on the mechanism of iron dissolution remained an open question. The present study used electrochemical impedance spectroscopy (EIS) as the main technique, to study the mechanism of iron dissolution in strong acid chloride solution with and without the presence of CO2. Results showed that the presence of chloride ions (0.5 M) decreased the rate of iron dissolution by competing with hydroxide ions to adsorb on the metal surface, forming chloride-containing intermediate species that participate in the iron dissolution reaction. The resulting decrease in the availability of hydroxide intermediates, which are more effective at enhancing the reaction rate compared to chloride-containing intermediates, leads to an overall decrease in the rate of iron dissolution. While the presence of CO2 increases anodic current density, EIS investigation revealed that neither aqueous CO2 nor other carbonic species directly react on the bare metal surface to form adsorbed intermediates involved in the anodic reaction. EIS investigation suggested that aqueous CO2 may induce changes in the chemical composition of adsorbed species, rate constants, and surface coverage, thereby altering the kinetics of the underlying reactions.

Mapping elemental solutes at sub-picogram levels during aqueous corrosion of Al alloys using diffusive gradients in thin films (DGT) with LA-ICP-MS

A novel approach using diffusive gradients in thin films (DGT) with laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for two-dimensional mapping of elemental solute release at sub-picogram levels during aqueous corrosion of Al alloys is presented. Evaluation of different DGT gels with mixed micro-sized binding phases (polyacrylamide-Chelex-Metsorb, polyurethane (PU)-Chelex-Metsorb, PU-Chelex-Zr(OH)4) demonstrated the superior performance of PU gels due to their tear-proof handling, low shrinkage, and compliance with green chemistry. DGT devices containing PU-Chelex-Zr(OH)4 gels, which have not been characterized for Al sampling before, showed quantitative uptake of Al, Zn, and Cu solutes over time (t = 4–48 h) with higher Al capacity (ΓDGT = 6.25 µg cm−2) than different gels. Application of PU-Chelex-Zr(OH)4 gels on a high-strength Al-Cu alloy (Al2219) exposed to NaCl (w = 1.5%, pH = 4.5, T = 21 °C) for 15 min in a novel piston-type configuration revealed reproducible patterns of Al and Zn co-solubilization with a spatial expansion ranging between 50 and 1000 µm. This observation, together with complementary solid-state data from secondary electron microscopy with energy-dispersive X-ray spectroscopy, showed the presence of localized pitting corrosion at the material surface. Detection limits for total solute masses of Al, Zn, and Cu were ≤0.72 pg, ≤8.38 pg, and ≤0.12 pg, respectively, for an area of 0.01 mm2, demonstrating the method’s unique capability to localize and quantify corrosion processes at ultra-trace levels and high resolution. Our study advances the assessment of Al alloy degradation in aqueous environments, supporting the design of corrosion-resistant materials for fostering technological safety and sustainability.Graphical

Investigation of kinetics and mechanisms of metallic beryllium corrosion for the management of radioactive wastes

Activated beryllium wastes are produced by the nuclear industry and have to be managed as radioactive waste during decommissioning and dismantling of nuclear facilities. One potential approach to the management of these wastes is their encapsulation and stabilization in cementitious matrices. The main issue with this conditioning is aqueous corrosion, leading to the hydrogen production and potential crack formation leading to a loss of confinement. To evaluate the suitability of different cement formulations, such as Ordinary Portland Cement (OPC) or magnesium phosphate cement for encapsulation of metallic beryllium, the corrosion behaviour of beryllium metal was investigated in solutions with different pHs. In alkaline solutions representative of OPC pore fluids (i.e. NaOH solutions with pH between 12.5 and 14), corrosion rates increase drastically with increasing pH. Investigations of the surface of the corroded beryllium samples by scanning electron microscopy indicate that pitting corrosion is the main corrosion mechanism under these conditions.Graphical abstract