Aggressive Anions Research Articles

Effect of Aggressive Anions on the Stress Corrosion Cracking of Stainless Steel in Hot Pressurized Alkaline Water

Abstract U-bend stress corrosion cracking (SCC) testing of low Cr ferritic (Type 409) and austenitic (Type 304L) stainless steel was conducted in a hot pressured alkaline water to study the effect of aggressive anions (Cl− and HS−) on the relative susceptibility. SCC was only observed in Type 304L when immersed in the solution that contained both aggressive anions. Critical factors were identified based on cross-section examination of the U-bends after exposure using complementary electron microscopy techniques. These factors include: (i) preferential oxidation of deformation bands (arising from cold working), (ii) Ni-S compound formation at the oxide/metal interface and (iii) S and Cl incorporation into the inward growing Cr-rich oxide. These critical factors were considered within an overall slip dissolution-type mechanism to account for the SCC observed.

Dendrimer-Encapsulated Halide Perovskite Nanocrystals for Self-Powered White Light-Emitting Glass.

Perovskite nanocrystals (PNCs) have attracted substantial attention due to their inspiring intrinsic merits such as low cost, high performance, and solution processability, but when it comes to the usage of blends of different colored PNCs with the purpose of covering the broadband spectrum field, the high degree of instability remains a major bottleneck. Herein, we report a family of dendritic ammonium ligands that act as stiff shell-encapsulating PNCs for improving their stability and suppressing ion permeability in mixed colloidal PNC solutions. The as-synthesized ligand-encapsulated PNCs notably achieve near-unity photoluminescence quantum yields (PLQYs) and strongly resist the unwanted ion exchange reaction under aggressive anion source attack. To fabricate self-powered white-emitting glass, the stabilized mixed colored PNCs were embedded into the laminated glass, which simultaneously acted as absorbers-emitters for luminescent solar concentrators (LSCs) and emitters for white light-emitting glass.

Understanding atomic interaction between cuprous oxide film and aggressive chloride solution

Considering the structural complexity of actual copper (Cu) passive films consisting of Cu2O, the multiple roles of aggressive chloride anion (Cl–) on Cu2O are revealed through first-principles calculations. Despite different Cl– adsorption susceptibilities of various Cu2O surfaces, similar surface O vacancy formation mechanisms promoted by Cl– adsorption are elucidated, accompanying with further Cu vacancy propagation. Increasing surface Cu vacancy concentration and unchanged Cu vacancy diffusion coefficient induced by Cl– adsorption lead to increasing diffusion flux. These results reveal the atomic interaction between Cu2O film and Cl ion, which is helpful to understand the depassivation mechanism of Cu.

Fabrication of Anion-Exchanged Electrodeposited Zn-Al Layered Double Hydroxides (LDHs) Coating on ZX21 Mg Alloy

Because of their low density and high specific strength, Mg alloys are considered promising lightweight alloys for various applications. However, due to the high electrochemical activity and poor corrosion resistance, surface modifications of Mg alloys are needed to increase the service life. Hence, an active layered double hydroxides (LDHs) coating was investigated in this study. Owing to the brucite-like layered structure, the weakly bonded interlayer anions can be easily exchanged with other anions in the environment. With the unique anion-exchange mechanism, LDHs coating provides dual protection to the Mg alloy substrate. It can not only act as a physical barrier but also absorb aggressive anions such as Cl- and release corrosion inhibitors to the environment.Compared to the commonly used hydrothermal method to fabricate LDHs coating, which requires high temperature and long process time, electrochemical deposition has the advantages of high deposition rates, simple experimental setup, and highly controllable process parameters. Therefore, in this study, a three-electrode electrochemical setup was used to fabricate Zn-Al LDHs coatings on a ZX21 Mg alloy. Moreover, different anions are intercalated into the interlayer galleries of the prepared Zn-Al LDHs coating through post anion-exchange processes.Through electrochemical analysis in a 3.5 wt% NaCl solution, the prepared anion-exchanged electrodeposited Zn-Al LDHs coating improved the corrosion resistance of ZX21 Mg alloy. Electrochemical impedance spectroscopy (EIS) showed that corrosion impedance increases, while potentiodynamic polarization curves revealed that the corrosion current density (i corr) of the coated sample was an order of magnitude lower than the ZX21 Mg alloy substrate. Besides the improvement of corrosion resistance, the formation mechanism of Zn-Al LDHs coating by electrodeposition was also investigated by electrochemical analysis and in situ optical microscopic (OM) observations. The corrosion behavior and microstructure of Zn-Al LDHs coating and the roles played by different intercalated anions will be discussed based on electrochemical analysis and microstructure characterizations. Figure 1

Extraordinary pitting resistance obtained by forming a partially recrystallized microstructure in a severely deformed 316LN stainless steel

Austenitic stainless steels with Cr-containing passive films are susceptible to pitting corrosion with the presence of aggressive anions. Repeated cold rolling and subsequent annealing were adopted to enhance the pitting resistance of a 316LN austenite stainless steel by balancing the deformed and the recrystallized microstructure. The highly ultra-fine grained structure formed during cold rolling gradually evolved to partially or fully recrystallized structures depending on the annealing parameters. Their microstructures were characterized by EBSD and the corrosion behaviors were evaluated through electrochemical techniques in a typical 3.5 wt% NaCl solution. The results show that the short-time annealed sample with a partially recrystallized structure exhibits extraordinary corrosion resistance compared with the cold rolled or the fully recrystallized one. This might be attributed to the elimination of the corrosion sensitive sites introduced during cold rolling by a proper extent of recrystallization without too many annealing twins, which are beneficial for pit nucleation.

Use of Multielectrode Arrays and Statistical Analysis to Investigate the Pitting Probability of Copper: Part II. The Effect of Sulfate and Bicarbonate

Copper and copper alloys have found applications in various industries. One of the main reasons Cu and its alloys are utilized widely is that they have sufficient corrosion resistance in key environments, such as seawater and anoxic solutions; however, localized corrosion processes might occur in the presence of aggressive anions, oxygen, or an increase in solution pH. In critical applications of Cu, the susceptibility of Cu to localized corrosion, specifically pitting, must be carefully considered, as it could lead to material failure. In this study, the pitting probability of Cu in unary (sulfate) and binary (sulfate + bicarbonate) solutions was investigated using electrochemical techniques in conjunction with statistical analysis. We determined pitting probabilities based on two different defining criteria for pitting susceptibility, one based on the probability that the corrosion potential, Ecorr, could exceed the passivity breakdown potential, Eb, and the other, a more conservative approach, based on the likelihood that Ecorr would be greater than the repassivation potential, Erp. The pitting probability of Cu did not change significantly with sulfate concentration at pH 8 but was found to increase with increasing [] up to 0.005 M at pH 9 and then to decrease with a further increase in [].

Hydroxyl radical production by abiotic oxidation of pyrite under estuarine conditions: The effects of aging, seawater anions and illumination

Pyrite is widely distributed in estuarine sediments as an inexpensive natural Fenton-like reagent, however, the mechanism on the hydroxyl radical (HO·) production by pyrite under estuarine environmental conditions is still poorly understood. The batch experiments were performed to investigate the effects of estuarine conditions including aging (in air, in water), seawater anions (Cl−, Br− and HCO3−) and light on the HO· production by pyrite oxidation. The one-electron transfer dominated the process from O2 to HO· induced by oxidation of pyrite. The Fe (oxyhydr)oxide coatings on the surface of pyrite aged in air and water consumed hydrogen peroxide while mediating the electron transfer, and the combined effect of the two resulted in a suppression of HO· production in the early stage of aging and a promotion of HO· production in the later stage of aging. Corrosion of the surface oxide layers by aggressive anions was the main reason for the inhibition of HO· production by Cl− and Br−, and the generation of Cl· and Br· may also play a role in the scavenging of HO·. HCO3− increased the average rate of HO· production through surface-CO2 complexes formed by adsorption on the surface of pyrite. The significant enhancement of HO· production under light was attributed to the formation of photoelectrons induced by photochemical reactions on pyrite and its surface oxide layers. These findings provide new insights into the environmental chemical behavior of pyrite in the estuary and enrich the understanding of natural remediation of estuarine environments.

Understanding the role of alloyed Ni and Cu on improving corrosion resistance of low alloy steel in the simulated Beishan groundwater

• The addition of Ni and Cu elements significantly inhibited the cathodic and anodic processes of steel corrosion. • Ni and Cu alloy elements were obviously enriched in the inner rust layer, which could improve the compactness of rust layer. • Fe 6 (OH) 12 SO 4 stably existed in the corrosion products of NiCu steel because Ni(Ⅱ) or Cu(Ⅱ) could substitute Fe(Ⅱ) of Fe 6 (OH) 12 SO 4 and increase its oxidation resistance. • Ni and Cu made Fe3O4 ionic selective by doping, which could repel the aggressive anions and improve the corrosion resistance. The corrosion behavior of NiCu low alloy steel and Q235 low carbon steel as the candidate materials for geological disposal containers of high-level radioactive waste in the simulated Beishan groundwater was comparatively studied by weight loss test, electrochemical measurements, scanning electron microscope (SEM), electron probe microanalysis (EPMA), X-ray diffraction (XRD), Raman spectrum and X-ray photoelectron spectroscopy (XPS). The electrochemical results showed that the corrosion potential of NiCu steel and Q235 steel gradually increased with the immersion time. Simultaneously, the cathodic process transited from hydrogen evolution reaction (HER) control to the rust reduction control, while the anodic process was always dominated by the active dissolution of iron. By comparison, both the cathodic resistance and the anodic dissolution resistance of NiCu steel corrosion were apparently higher than that of Q235 steel. The results of rust layer characterization indicated that Ni and Cu elements could be enriched in the inner rust layer of NiCu steel and the rust layer was more compact. As the main corrosion products, the content of α-FeOOH in the rust layer of NiCu steel was obviously increased more than that of Q235 steel. Fe 6 (OH) 12 SO 4 stably existed in the corrosion products of NiCu steel because Ni(II) or Cu(II) could substitute Fe(II) of Fe 6 (OH) 12 SO 4 and increased its oxidation resistance. Moreover, Ni and Cu could also make Fe 3 O 4 ionic selective by doping. After the long-term immersion, the corrosion mass loss of NiCu steel was significantly lower than Q235 steel, which further confirmed the benefits of Ni and Cu alloying on improving the steel corrosion resistance.

Molecular Dynamics Model to Explore the Initial Stages of Anion Exchange involving Layered Double Hydroxide Particles.

A classical molecular dynamics (MD) model of fully unconstrained layered double hydroxide (LDH) particles in aqueous NaCl solution was developed to explore the initial stages of the anion exchange process, a key feature of LDHs for their application in different fields. In particular, this study focuses on the active corrosion protection mechanism, where LDHs are able to entrap aggressive species from the solution while releasing fewer corrosive species or even corrosion inhibitors. With this purpose in mind, it was explored the release kinetics of the delivery of nitrate and 2-mercaptobenzothiazole (MBT, a typical corrosion inhibitor) from layered double hydroxide particles triggered by the presence of aggressive chloride anions in solution. It was shown that the delamination of the cationic layers occurs during the anion exchange process, which is especially evident in the case of MBT-.

High corrosion resistance duplex fcc + hcp cobalt based entropic alloys: An experimental and theoretical investigation

A series of duplex fcc + hcp Co-based entropic alloys are being discovered as a new category of entropic alloys with outstanding mechanical properties, especially to overcome a typical mechanical trade-off between strength and ductility. In this work, CALPHAD-based (CALculation of PHAse Diagram) thermodynamic calculations were performed to facilitate alloy design and to understand corrosion behaviors. The kinetics of the electrochemical corrosion for designed alloys in typical aggressive anion Cl- was investigated by electrochemical tests, including open circuit potential (OCP), polarization and cyclic polarization curves, and electrochemical impedance spectroscopy (EIS). The valence state and the surface morphologies of the passive films were investigated by X-ray photoelectron spectroscopy (XPS) and atomic force microscope (AFM). High corrosion resistance materials with high strength and ductility performances were discovered in the present work. Except for Ni-oxides, various spinel compounds and many other oxides including Co2O3, Cr2O3, Fe2O3, MnO, MoO3, CoCr2O4, FeCr2O4, CoFe2O4, and CoMoO4 were observed in the passive films. The adsorbed and penetrated corrosive anion Cl- will be prone to breakdown the passive films with less Cr2O3, CoCr2O4 and MoO3 to form pitting corrosion (also include other localized corrosion, such as intergranular corrosion and crevice corrosion). The microstructure of the hcp martensite with the fcc matrix has played an important role in the propagation of the localized anodic dissolution in the form of cleavage and quasi-cleavage. The theoretical calculations are in good agreement with the experimental observations. This paper paves a way for the future development of high-performance Co-based entropic alloys served in some harsh environments.

Crack branching behavior and amorphous film formation mechanism during SCC expanding test for multi-layers weld metal of NiCrMoV steels

Multi-layer weld metal of NiCrMoV steels used in nuclear rotor was adopted to perform stress corrosion cracking (SCC) test at 180 ℃, which indicated the crack growth rate in 3.5% NaCl solution was lower than that in pure water. The results obtained from high resolution transmission electron microscopy (HRTEM) analysis revealed that the combined effect of crack branching behavior and amorphous film made contributions to the slower crack growth rate. The aggressive Cl− ions invaded grain in multi-directions that was promoted by dislocation motion, facilitating the main crack to bifurcate. Besides, nanocrystals also enhanced branching behavior by deflecting the crack growth path. An amorphous film forming in crack evolved from the disorder of atom arrangement produced by dislocation accumulation and grew stably with the supplement of carbon atom generated in selective corrosion. The complete amorphous film was absent connected path for migration of aggressive anions, thus weakened the driving force for crack propagation and improved resistance to localized corrosion attack.

Investigation of failure mechanisms and remaining life prediction of firewater pipelines used in industrial applications

Firewater (FW) pipelines network maintenance and monitoring are of utmost importance since they are not easily accessible for inspection. Failure and corrosion of carbon steel FW pipes, particularly localized corrosion, can propagate leaks and bursts of pipelines, which leads to expensive repairs or replacement, or even uncontrolled situations during an emergency. Therefore, being aware of the pipeline conditions, predicting their failure mechanisms, their remaining life, planning to manage emergencies, and evaluating their conditions are essential. In this study, visual inspection, metallurgical examinations using optical microscopy in combination with scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD), and corrosion test using a three-electrode system were employed to determine the cause of failure. Also, the water samples were subjected to various chemical and bacterial analyses. Corrosion and scale-forming potential, Physico-chemical properties, sulfate-reducing bacteria, Iron-reducingbacteria, and total bacterial count were investigated on water samples to evaluate the corrosion conditions of FW pipes. Furthermore, the remaining life prediction and monitoring of the pipelines have been studied based on laboratory simulation experiments and advanced non-destructive tests (NDT) by using Long Range Ultrasonic Testing (LRUT) and Phased Array Ultrasonic Testing (PAUT). The results indicate that the oxygen corrosion attack especially the accumulation of air bubbles (dissolved oxygen), forming tubercles, and aggressive anions (Cl- and SO42-) that are the root causes of the pipeline's failure. It can happen in general and localized forms such as localized pitting corrosion, tuberculation, top-of-the water line corrosion (TWLC), and cavitation damage. Also, by comparing NDT tests and laboratory experiments results, the remaining life results in state 2 are in good agreement. Thus, the laboratory simulation experiments are verified and can be used as a desirable indicator for the remaining life of FW pipelines and strategies for improved durability design and maintenance.

Inhibitory effects of hematite nanoparticles on corrosion protection function of TiO2 coating prepared by plasma electrolytic oxidation

Protective oxide coatings were prepared on titanium substrates using the plasma electrolytic oxidation process, and the inhibitory role of hematite nanoparticles (HNPs) in their corrosion performance was evaluated by studying the formation and growth behavior. The results confirmed that the addition of HNPs up to a maximum amount of 3 g·L−1 to the phosphate-based electrolyte softened and stabilized the electrochemical events during titanium oxidation, resulting in an oxide layer with a more uniform microstructure, as well as less porosity and surface roughness. The participation of HNPs in the coating preparation accelerated the growth rate, promoted the anatase-rutile transformation, and reduced the inherent defects. Thus, the thermodynamic stability of the coatings in the corrosive medium improved and the dissolution kinetics of the substrate diminished. Modeling the data obtained from electrochemical impedance spectroscopy revealed that the incorporation of HNPs up to the maximum amount into the coatings increased the corrosion resistance of outer and inner parts of their bilayer microstructure by 5.18 and 9.88 times, respectively. Furthermore, Mott-Schottky analysis demonstrated that the surface reactivity of the coatings with aggressive anions diminished due to the reduction of donor concentration and more negative flat band potential, which proved the inhibiting effects of HNPs.

Effects of Laser Glazed Surface on Pitting Corrosion of Nickel Alloy 718 in Acidic and Seawater Environments

Studies on the effects of laser glazed and unglazed sample surfaces on the pitting corrosion resistance of nickel alloy 718 have been carried out. Both sample surfaces of nickel alloy 718 were cut to different dimensions for pitting corrosion tests using potentiostatic polarization process. The alloy samples used for electrochemical testing were connected to a flexible wire joined by spot weld process. The alloy samples were coated with low viscous polymeric wax leaving the surface areas to be tested exposed to seawater and one mole concentration of hydrochloric acid environments. These samples which are working electrodes have electrical connection between reference electrode and counter electrode and the entire system were connected to computer with PSTrace software that stands as potentiostat. Pre and post morphological examination of the sample surfaces were done using confocal laser scanning microscopy and scanning electron microscopy respectively. The results of pitting corrosion tests showed that the glazed and unglazed alloy sample surfaces immersed in seawater environment suffered from pitting corrosion as a result of the presence of pit initiation sites developed during surface laser treatment and also the presence of some aggressive anions like Cl^-, SO₄^- etc in the environment which migrated into the pits due to electrostatic balance and escalated pitting corrosion; while the samples of both surfaces immersed in 1MHCl suffered more from general corrosion. Post pitting corrosion examinations revealed that corrosion oxide films formed on the sample surfaces in acidic and alkaline environments were not protective as they flaked and exposed the sample surfaces to more corrosion attack.

Hierarchical Porous Structure of Niobium Prepared By an Electrochemical Method

Fabrication of meso-/macro-porous electrode materials is known to be one of the effective ways to improve the performance of functional electrochemical devices since the porous structure would provide large surface area and allow rapid transport of atoms and ions. Recently, niobium (Nb) or Nb-based porous material has drawn much attention because of its highly versatile chemical and physical properties. There are various ways to form the porous Nb structure, such as hydrothermal, sol-gel, anodic oxidation and electrochemical etching methods. Among them, an electrochemical etching method is noteworthy because it is cost-effective, and the porous structure of the surface is easily tunable by adjusting etching conditions. Nevertheless, the general use of a noxious chemical (e.g. HF) for Nb porous structure formation needs to be avoided and then the creation of highly-porous Nb structure using F--free, more environmentally-benign chemical is still a challenge.In this work, the novel hierarchical Nb porous structure is created by an electrochemical method by using F--free etching solution. In particular, it is confirmed that the pulse etching is far more effective to form a hierarchical or self-similar fractal porous structure of Nb than conventional continuous etching, most likely due to the repetitive and incessant supply of aggressive anion. It is further proved experimentally that the initial concentration of aggressive anion is one of the essential factors in forming well-defined, high-order hierarchical Nb porous structure. Under the optimal etching condition, the porous Nb structure with more than 3 hierarchical order can be successfully created by single etching process.On the basis of the experimental observation of pore shape, the formula for the surface area of porous Nb is derived as a function of the hierarchical order of pore. From the comparison of the theoretically calculated surface area with the experimentally estimated one, the actual pore shape along with the hierarchical order of pores can be reasonably analyzed. In this presentation, the governing factors to construct a hierarchical Nb porous structure are suggested. Moreover, the utility of the formula between surface area and hierarchical pore order is discussed in terms of the non-uniformity of porous structure and hypotheses used to derive it.

Investigation of the Localized Corrosion of Ni-Cr-Mo-W Alloy UNS N06022 in Aprotic Solvents at Room Temperature

Syntheses of pharmaceuticals often require a series of intermediate steps involving reactions in aprotic organic solvents. Some of these solutions can be aggressive towards the metallic materials that constitute the reaction vessels used, so often corrosion-resistant alloys (CRA) such as the Ni-Cr-Mo-W UNS N06022 are employed. Such materials are expensive, but their use is required to prevent contamination of the product by metal ions. Ni-Cr-Mo-W alloys are known to exhibit outstanding corrosion resistance in reducing and oxidizing aqueous solutions as a result of their passive oxide film. However, the application of passive alloys in nonaqueous solvents raises additional concerns due to: i) limited availability of oxygen atoms for passivation; ii) different behavior of aggressive anions and acids as a result of the solvent’s physicochemical properties. Nevertheless, the literature on corrosion of CRA is focused on behavior in aqueous solutions and the literature on corrosion in organic solvents lacks information on the application of commercial alloys. The aim of this work is to investigate the corrosion of Ni-Cr-Mo-W alloys in aprotic organic solvents and to understand the influence of properties of the solvent on the susceptibility to pitting and to uniform corrosion, at room temperature.Preliminary work was carried out with anhydrous acetonitrile solutions containing HCl and the oxidant 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ). Mass loss and electrochemical tests have shown that alloy N06022 exhibits high-rate dissolution in such conditions. The corrosion rates observed after 24 h of immersion are greater than 10 mm/year, which is remarkably high when compared with the existing literature on corrosion of Ni-Cr-Mo alloys. Moreover, in neutral acetonitrile containing chloride, N06022 undergoes pitting at much lower Cl– concentrations and temperature than in aqueous solutions. In order to understand the enhanced susceptibility to pitting and uniform corrosion in aprotic solvents, potentiodynamic polarizations and electrochemical impedance spectroscopy were performed in various solution compositions, followed by surface characterization with scanning electron microscopy. The correlation of passivation and breakdown phenomena with variables of importance, namely water content, chloride concentration, and acidity will be investigated. Ultimately, this study will provide fundamental understanding of the passivity of Ni-based alloys in organic solvents, assisting the selection of materials for nonaqueous applications.

Pitting Corrosion Probability of Copper in Solutions Containing Chloride and Sulfate Using Coupled Multielectrode Arrays

The preferred disposal method for used nuclear fuel is to seal it in containers emplaced in a deep geologic repository (DGR) in a suitable rock formation. In Canada, the container is a robust steel vessel coated with 3 mm of Cu as a corrosion barrier. Eventually, the DGR environment will become anoxic, and in the absence of oxygen copper is thermodynamically stable in water. However, since exposure conditions will initially be oxidizing due to the presence of trapped O2 upon sealing the DGR, there is a possibility of localized corrosion to occur. Mass balance calculations show that uniform corrosion during this period will be within the designed corrosion allowance, however, since the Cu coating is relatively thin and the required lifetime is long, the risk of pitting corrosion during this period must be carefully evaluated.Pitting corrosion susceptibility is determined by the corrosion potential of the material (Ecorr, the potential at which the rates of all anodic and cathodic reactions are equal), and the breakdown potential (Eb, the potential at which the copper oxidation rate on the surface increases abruptly due to the breakdown of the protective film), both of which are distributed parameters. This is due to the stochastic nature of passive film rupture and any uncontrollable variations in the structure and local environment at the metal surface. It is important to note that the analysis is based on the concept that pitting is only possible if the Ecorr is equal to, or more positive than the Eb.Our previous studies showed a passive behavior of copper surface when exposed to high pH solutions. In this work, a multielectrode array was used to obtain a statistically meaningful set of potential measurements through the simultaneous monitoring of 30 electrodes to determine their corrosion and breakdown potentials. From the extensive database that acquired, the Ecorr and Eb distributions were defined for the copper electrodes exposed to solutions containing various chloride concentrations and a more thorough evaluation of the relative values of Ecorr and Eb has undertaken to determine the susceptibility to pitting.Experiments were conducted using a multielectrode array in chloride and sulfate containing solutions at 25 °C and pH 8 and 11. In alkaline solutions, the copper oxide is more stable and can potentially form a passive film, whereas chloride and sulfate promote the breakdown of the passive film. As the concentration of aggressive anions increased, the values of Ecorr and Eb decreased, suggesting that the solubility of copper increased with in the presence of both chloride and sulfate. However, there is a critical sulfate concentration (~5 × 10-3 M) that above which the pitting probability of copper decreased.In general, the possibility of pitting increased with growing overlap between the distribution curves of Ecorr and Eb. To evaluate the possibility of pitting, histograms and distribution curves of Ecorr and Eb in the solutions that contain different chloride and sulfate concentrations were compared. In lower chloride concentrations, there was a very small overlap between distributions of Ecorr and Eb values; therefore, the possibility of pitting under these conditions is very low. On the other hand, a high chloride concentration at high pH indicated a higher probability of pitting, as the overlap between Ecorr and Eb distributions increased. Also, the extent of the passive zone decreased with increasing chloride concentration. In solutions containing sulfate content, the overlap between Ecorr and Eb increased with increasing sulfate concentration up to a certain content (~5 × 10-3 M), after this point the overlap decreased as the sulfate concentration increased. The results from potentiodynamic experiments indicated that increasing the chloride concentration resulted in decreased the extent of the passive zone; however, the sulfate did not seem to play a significant role in changing the extent of the passive zone. Figure 1

The Pitting Corrosion Probability of Copper in Solutions Containing Chloride and Sulfate Using Coupled Multielectrode Arrays

The preferred disposal method for used nuclear fuel is to seal it in containers emplaced in a deep geologic repository (DGR) in a suitable rock formation. In Canada, the container is a robust steel vessel coated with 3 mm of Cu as a corrosion barrier. Eventually, the DGR environment will become anoxic, and in the absence of oxygen copper is thermodynamically stable in water. However, since exposure conditions will initially be oxidizing due to the presence of trapped O2 upon sealing the DGR, there is a possibility of localized corrosion to occur. Mass balance calculations show that uniform corrosion during this period will be within the designed corrosion allowance, however, since the Cu coating is relatively thin and the required lifetime is long, the risk of pitting corrosion during this period must be carefully evaluated.Pitting corrosion susceptibility is determined by the corrosion potential of the material (Ecorr, the potential at which the rates of all anodic and cathodic reactions are equal), and the breakdown potential (Eb, the potential at which the copper oxidation rate on the surface increases abruptly due to the breakdown of the protective film), both of which are distributed parameters. This is due to the stochastic nature of passive film rupture and any uncontrollable variations in the structure and local environment at the metal surface. It is important to note that the analysis is based on the concept that pitting is only possible if the Ecorr is equal to, or more positive than the Eb.Our previous studies showed a passive behavior of copper surface when exposed to high pH solutions. In this work, a multielectrode array was used to obtain a statistically meaningful set of potential measurements through the simultaneous monitoring of 30 electrodes to determine their corrosion and breakdown potentials. From the extensive database that acquired, the Ecorr and Eb distributions were defined for the copper electrodes exposed to solutions containing various chloride concentrations and a more thorough evaluation of the relative values of Ecorr and Eb has undertaken to determine the susceptibility to pitting.Experiments were conducted using a multielectrode array in chloride and sulfate containing solutions at 25 °C and pH 8 and 11. In alkaline solutions, the copper oxide is more stable and can potentially form a passive film, whereas chloride and sulfate promote the breakdown of the passive film. As the concentration of aggressive anions increased, the values of Ecorr and Eb decreased, suggesting that the solubility of copper increases with in the presence of both chloride and sulfate. However, there is a critical sulfate concentration (~5 × 10-3 M) that above which the pitting probability of copper decreases.In general, the possibility of pitting increases with growing overlap between the distribution curves of Ecorr and Eb. To evaluate the possibility of pitting, histograms and distribution curves of Ecorr and Eb in the solutions that contain different chloride and sulfate concentrations were compared. In lower chloride concentrations, there was a very small overlap between distributions of Ecorr and Eb values; therefore, the possibility of pitting under these conditions is very low. On the other hand, a high chloride concentration at high pH indicated a higher probability of pitting, as the overlap between Ecorr and Eb distributions increased. Also, the extent of the passive zone decreased with increasing chloride concentration. In solutions containing sulfate content, the overlap between Ecorr and Eb increased with increasing sulfate concentration up to a certain content (~5 × 10-3 M), after this point the overlap decreased as the sulfate concentration increased. The results from potentiodynamic experiments indicated that increasing the chloride concentration resulted in decreased the extent of the passive zone; however, the sulfate did not seem to play a significant role in changing the extent of the passive zone.

Effect of Aluminum Oxide on the Performance of Ionic Liquid-Based Aluminum–Air Battery

The aluminum–air (or oxygen) battery has received intense attention in the past because of its excellent benefits such as low cost and high energy density, but due to the challenging issues such as hydrogen evolution and inactive oxide film formation on the Al surface, it could not be fully applied. In this study, 1-Ethyl 3-Methyl Imidazolium Chloride ([EmIm]Cl) and aluminum chloride (AlCl3) are applied to resolve the aforementioned issues. Ex situ component-level and in situ cell-level open circuit voltage (OCV) tests combined with the physics-based model analyses were conducted to investigate the electrochemical reaction behaviors of the Al–air cell. Especially, the effect of aluminum oxide formation on the anode- and cathode-side reactions were analyzed in detail. The oxide film formed at the Al surface strongly was found to significantly impede the electrochemical reaction at the surface, and the film growth was controlled by decreasing the surface tension by aggressive anions. In the cathode side, the aluminum oxide precipitated in the porous cathode electrode was found to decrease the porous reaction area and block reactant access into the reaction sites. The effects of O2 solubility in the electrolyte, initial porosity and thickness of the porous electrode are compared in detailed, and optimal thickness is suggested.

Near-field corrosion interactions between glass and corrosion resistant alloys

This study explores the corrosion interactions between model nuclear waste glass materials and corrosion resistant alloys, under accelerated conditions that simulate the near field of a nuclear waste repository. The interactions between the corrosion of stainless steel (SS) 316, alloy G30, or alloy 625, and international simple glass or soda-lime silica glass are systematically studied. The dissimilar materials were exposed in close proximity to each other in different electrolytes at 90 °C. After exposure, the glass surface exposed near metals showed different regimes of corrosion, with distinct surface morphologies and chemistries that were likely affected by the local environment created by the localized corrosion of metals. Surface and solution analyses showed that the corrosion rate of glass was enhanced by the presence of metals. Infrared spectroscopy data suggested the local build-up of stresses in the contact area of glass, which may lead to the mechanical instability of the glass alteration layer. On the other hand, the effect of glass on metal corrosion is strongly dependent on the leaching solution. In electrolytes containing abundant aggressive anions such as Cl−, glass seems to suppress the localized corrosion of SS by the precipitation of a Si-rich surface film that protects the SS substrate from solutions. However, in less aggressive electrolytes, the corrosion rate of SS was increased by the presence of glass corrosion products. Overall, our study showed that the hidden and localized damage on glass in contact with metals may enhance the release rate of glass components compared to typical uniform glass corrosion.