Electrochemical corrosion of unalloyed copper in chloride media--a critical review

The literature dealing with the electrochemical corrosion characteristics of unalloyed copper in aqueous chloride media is examined. The enormous quantity of polarisation and mixed/corrosion potential data that has been made available in the literature over the last 50 years has been compiled and discussed in a comprehensive review. For a wide range of electrode geometries, the importance of the chloride ion and the mass transport of anodic corrosion products on the corrosion behaviour of copper are made clear for both freshly polished and ‘filmed’ surfaces.     

Effect of cathodic protection on corrosion of pipeline steel under disbonded coating

In this work, a test rig was developed to study the effect of cathodic protection (CP) on corrosion of X70 pipeline steel in the crevice area under disbonded coating through the measurements of local potential, solution pH and dissolved oxygen concentration. Results demonstrated that, in the early stage of corrosion of steel, CP cannot reach the crevice bottom to protect steel from corrosion due to the geometrical limitation. Corrosion of steel occurs preferentially inside crevice due to a separation of anodic and cathodic reaction with the depletion of dissolved oxygen in the crevice solution. The main role of CP in mitigation of sequential corrosion of steel in crevice under disbonded coating is to enhance the local solution alkalinity. With the increase of distance from the open holiday, a high cathodic polarization is required to achieve appropriate CP level at crevice bottom. A potential difference always exists between the open holiday area and inside crevice, reducing the CP effectiveness.     

Optimizing the electrode position in sacrificial anode cathodic protection systems using boundary element method

In this paper, a sacrificial anode cathodic protection problem of 2D steel storage tank was simulated using boundary element method. The tank was protected by a zinc anode located directly on structure wall. Data obtained from potentiodynamic measurements were used as boundary condition. In this study, optimum location of the anode was determined, and the influence of anode length and paint defect on the level of protection provided by system were investigated. This study showed that boundary element method is beneficial in modeling and analyzing cathodic protection systems and calculated results were consistent with expectations from the basic corrosion concepts.     

Disbonding of underwater-cured epoxy coating caused by cathodic protection current

Cathodic disbonding of the underwater-applied, ultra-thick, solvent free epoxy coating subjected to various levels of cathodic protection was investigated during the period of the coating cure. The results indicate that the partially cured coating was of low resistivity, between 10³ and 10⁵ Ω cm² for the cathodic polarization of on-potentials between −0.98 and −1.4 V_Ag/AgCl/sw. The coating was shown to be capable of withstanding normal levels of cathodic protection between off-potentials of −0.8 and −1.1 V_Ag/AgCl/sw while the IR drop, introduced by the coating in the same potential range, increased from 0.06 to 0.1 V and has to be taken into account at the design stage of the cathodic protection system. Beneficial influence of calcareous deposit formation on the cathodic protection current was confirmed, particularly for the failed coating. The initial period (1 week) of coating cure was shown as the most critical for disbonding processes caused by the excessive cathodic polarization.     

SVET and SECM imaging of cathodic protection of aluminium by a Mg-rich coating

The mechanism of cathodic protection of an aluminium substrate by a Mg-rich coating was investigated using localized techniques. Both scanning vibrating electrode techniques (SVET) and scanning electrochemical microscopy (SECM) were used to investigate the processes occurring at the surface of exposed metal when electrically connected or disconnected in a galvanic couple with the Mg-rich coating. The SVET has shown the evolution of the pit activity with time under conditions of sacrificial protection, whereas the SECM allowed indirect sensing of the cathodic activity above the electrodes. It was shown that the cathodic protection provided by magnesium to aluminium substrates acts by both preventing pit nucleation and inhibiting the growth of the pre-existing pits.     

Influence of conductivity on cathodic protection of reinforced alkali-activated slag mortar using the finite element method

Cathodic protection (CP) is considered to be the only rehabilitation method for chloride-induced rebar corrosion in reinforced concrete structures. The protection current distribution depends on several parameters, such as the geometry and number of rebars and the concrete resistivity. In order to investigate the influence of concrete resistivity on the possibilities and limitations of rebar protection, this paper presents a numerical approach based on the finite element method (FEM) in conjunction with laboratory results to determine its impact on the CP of alkali-activated slag mortar. An ordinary Portland cement was also tested for comparative purposes.     

Modeling pipeline crevice corrosion under a disbonded coating with or without cathodic protection under transient and steady state conditions

Underground steel pipelines are protected by coatings and cathodic protection (CP). The pipeline corrosion occurs when the coating is disbonded away from a defect or holiday to form a crevice and the corrosion rate varies temporally and spatially in the crevice. In the presence of dissolved oxygen (O₂) in soil ground water, a differential O₂ concentration cell may develop in the crevice because O₂ diffuses more readily into the crevice through the holiday than through the disbonded coating. CP can decrease or eliminate the O₂ concentration cell depending on the potential applied at the holiday. Since the coatings are usually non-conductive, CP is unable to protect the steel surface deep inside the crevice. The transport of dissolved O₂, and that of dissolved carbon dioxide (CO₂) if present, into the crevice through holiday can be key to determining the crevice corrosion rate. In this work, the transient and steady state behavior of the corrosion process is investigated. The effect of the cathodic portion of iron vs. ferrous ion redox reaction on the crevice corrosion rate, which is often neglected traditionally, is further studied. At steady state, the effect of dissolved O₂ on the crevice corrosion rate and the added effect of dissolved CO₂ are mathematically modeled.     

A peculiar cathodic process during iron and steel corrosion in sulfate reducing bacteria (SRB) media

Features related to the cathodic reduction of iron sulfides precipitation on iron surface during its exposure to SRB culture were studied. Electrochemical measurements were performed with pure iron and platinum electrodes plated with a thin iron film in de-aerated SRB culture. The study reveals that iron sulfide precipitation is being cathodically reduced just below a potential of −0.1 V_SCE, and if iron corrosion process occurs at potentials below that threshold potential, then the reduction of iron sulfide may provide an alternative cathodic depolarization mechanism in SRB. This cathodic process can maintain iron and corrosion at potentials above RHE potential.     

Corrosion monitoring and materials selection for automotive environments by using Atmospheric Corrosion Monitor (ACM) sensor

Severity of corrosion damage in automobiles depends on use environments and parts. Corrosion life prediction is a key technology for the optimum selection of materials. The Fe–Ag type Atmospheric Corrosion Monitor (ACM) sensor has been the object of many studies from this viewpoint. In the present study, ACMs were installed on various parts of a monitoring test vehicle and the corrosivity of the environments of those parts was evaluated. To simulate different use environments, pure water and salt water were sprayed on the right and left halves of the vehicle body. The corrosion behavior in each part was characterized by the output of the ACM sensor against atmospheric parameters and driving history. Corrosion of test coupons (cold-rolled steel, Zn-coated steel) was also measured at the same positions. The corrosion rates of these exposure test specimens showed a good correlation with the average daily charge calculated from the sensor output. These results demonstrated the possibility of corrosion life prediction and materials selection based on ACM monitoring results. It was concluded that ACM monitoring is applicable to corrosivity evaluation of automotive environments, including both specific parts of automobiles and automobile use environments.     

Comparison of testing solutions on the protection of Al-alloys using a Mg-rich primer

Magnesium-rich coatings present a new and challenging field of development for the corrosion protection of aluminium structures. These coatings are capable of sacrificial protection, but assessment of their efficiency and durability can be strongly affected by the testing environment. In this work two solutions commonly used in our studies are compared: 0.1% NaCl and dilute Harrison solution (DHS). The corrosion behaviour of two aluminium alloys coated with a magnesium-rich coating, of pure magnesium and of the bare aluminium substrates was assessed in the two solutions using electrochemical techniques. The corrosion rate of pure magnesium was higher in DHS, although the dissolution rate of the magnesium embedded in the polymer matrix was not significantly affected. The impedance spectra of the scribed samples resembled that of the bare substrates in NaCl solution but not in DHS.     

Investigating the mechanism of stress corrosion cracking in near-neutral and high pH environments for API 5L X52 steel

Stress corrosion cracking behaviour of API-5L-X52 steel under cathodic protection in near-neutral and high pH conditions was studied using slow strain rate test method and electrochemical measurements. The slow strain rate test showed ductile and brittle fracture feature at low and high applied potentials, respectively. In order to identify the mechanism contributes in stress corrosion cracking; the electrochemical potentiodynamic polarisation test was done at fast and slow sweep rate. The results revealed that at near-neutral pH condition the anodic dissolution at crack tip was the dominant mechanism. While at high pH medium, the hydrogen based mechanism was dominant.     

Corrosion behaviour of an aluminized nickel coating in a carbon dioxide capture process using aqueous monoethanolamine

Carbon steel A106 with an aluminized Ni coating was tested in a 5 mol/l (M) monoethanolamine (MEA) with a carbon loading of 0.2 mol/mol MEA at 80 °C using polarization resistance, Tafel, and electrochemical impedance spectroscopy (EIS) techniques. Surface morphology and elemental line profile of the coating were examined before and after a 900 °C heat-treatment in atmosphere environment. X-ray diffraction (XRD) results showed that the coating surface constitutes transformed from Ni₂Al₃ to Al-rich NiAl after heat-treatment. The electrochemical results show that the heat-treated coating displays outstanding corrosion performance with the conditions tested.     

Effect of CO2 and R-ratio on near-neutral pH stress corrosion cracking initiation under a disbonded coating of pipeline steel

This study investigates the role of CO₂ and cyclic stress R-ratio (R = minimum stress/maximum stress) on near-neutral pH SCC initiation mechanism(s) under a disbonded coating of pipeline steel protected by cathodic protection (CP). It was found that depending on CO₂ concentration and level of CP, different localized environments with various pH could be formed under the disbonded coating. When cyclic loading was applied, different SCC initiation mechanisms were involved depending on the pH of the localized environments. Reducing the R-ratio had different effects on the initiation mechanisms.     

Corrosion control of copper in nitric acid solutions using some amino acids - A combined experimental and theoretical study

Inhibition performance of three amino acids, namely l-methionine (MIT), l-methionine sulfoxide (MITO) and l-methionine sulfone (MITO2), as corrosion-safe inhibitors for copper surface in 1.0 M nitric acid was investigated by weight loss, dc polarization and ac impedance techniques. A significant decrease in the corrosion rate of copper was observed in the presence of the investigated compounds. The reactivates of the compounds under investigation were analyzed through Fukui functions, to explain their inhibition performance. Simulation techniques incorporating molecular mechanics and molecular dynamics were used to simulate the adsorption of l-methionine derivatives, on copper (1 1 1) surface in nitric acid.     

Corrosion control of mild steel using 3,5-bis(4-methoxyphenyl)-4-amino-1,2,4-triazole in normal hydrochloric acid medium

The inhibition performance of the 3,5-bis(4-methoxyphenyl)-4-amino-1,2,4-triazole (4-MAT) on mild steel in normal hydrochloric acid medium (1 M HCl) at 30 °C was tested by weight loss, potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS) techniques. This organic compound inhibits the acidic corrosion even at very low concentration, reaching a value of inhibition efficiency up to 98% at a concentration of 3 × 10⁻⁴ M. The results obtained from the different corrosion evaluation techniques are in good agreement. Polarisation curves indicate that 4-MAT is a mixed inhibitor, affecting both cathodic and anodic corrosion currents. Data, obtained from EIS measurements, were analyzed to model the corrosion inhibition process through appropriate equivalent circuit model, a constant phase element (CPE) has been used. The adsorption of 4-MAT on the steel surface, in 1 M HCl solution, obeys to Langmuir’s isotherm with a very high negative value of the free energy of adsorption ΔG°_ads (chemisorption). X-ray photoelectron spectroscopy (XPS) was carried out to establish the mechanism of corrosion inhibition of mild steel in 1 M HCl medium in the presence of 3,5-bis(4-methoxyphenyl)-4-amino-1,2,4-triazole (4-MAT).     

Corrosion protection of magnesium AZ31 alloy using poly(ether imide) [PEI] coatings prepared by the dip coating method: Influence of solvent and substrate pre-treatment

In this study, investigations on the protectiveness of poly(ether imide) coatings against corrosion of magnesium AZ31 alloy sheets are performed. The coatings were prepared in different pre-treated substrates by the dip coating method using N′N′-dimethyl acetamide (DMAc) and N′-methyl pyrrolidone solutions. The optimal performance was obtained for hydrofluoric acid treated substrates coated using DMAc solution (coating thickness 13 μm) which showed impedances in the order of 10⁷ Ω cm² even after more than 3300 h of exposure to a 3.5 wt.% NaCl solution. This high performance is associated to an acid–base interaction at the interface as observed by X-ray photoelectron spectroscopy.     

Changes in mass and stress during anodic oxidation and cathodic reduction of the Cu/Cu2O multilayer film

The anodic oxidation and cathodic reduction processes of the Cu/Cu₂O multilayer film and pure Cu film in pH 8.4 borate buffer solution were analyzed by electrochemical quartz crystal microbalance (EQCM) for gravimetry and bending beam method (BBM) for stress measurement. The mass loss of the multilayer film during anodic oxidation at 0.8 V (SHE) in the passive region was less than that of the pure Cu film. The comparison between current transients and mass changes during anodic oxidation has succeeded in separating the anodic current density into two partial current densities of oxide film growth, i_O^2-, and of Cu²⁺ dissolution through the passive film, i_Cu²⁺. As a result, in the case of the pure Cu film, the anodic current density was mainly due to i_Cu²⁺, while in the case of the multilayer film, i_Cu²⁺ was almost equal to i_O^2-. The compressive stress for the multilayer film was generated during anodic oxidation, while the tensile stress for the pure Cu film was generated.The mass loss of the multilayer film during cathodic reduction at a constant current density (i_c = −20 μA cm⁻²) was significantly less than that estimated from coulometry, suggesting that H₂O produced by cathodic reduction remained in the multilayer film. The compressive stress was generated during cathodic reduction of the multilayer film, which was ascribed to H₂O remained in the multilayer film.     

Evaluation of the effect of dosage, pH and contact time on high-dose phosphate inhibition for copper corrosion control using response surface methodology (RSM)

The response surface methodology (RSM), particularly Box-Behnken design model, was used in this study to obtain the optimum operating conditions for reduction of copper corrosion by-product release using high-dose polyphosphate inhibition. Furthermore, the RSM was also applied to study the main and interactive effects of the parameters investigated. Both analysis of variance (ANOVA) and coefficient of determination (R²) showed that the RSM approach was appropriate for the optimization of high-dose polyphosphate inhibition. The main effects of polyphosphate dosage and pH were found significant in reducing copper release using high-dose polyphosphate whereas the effect of contact time was less significant. In terms of interactions between the effects, the relation between polyphosphate dosage and the pH was the most significant. The optimal polyphosphate dosage, pH and contact time were found to be 22-28 mg/L of polyphosphate as P, 9-10, and 36 h, respectively. The highest total copper release reduction was estimated as 95.86% under the optimum condition. Surface analysis using both SEM-EDX and XRD discovered that cupric phosphate was present on the copper surface treated with high-dose polyphosphate inhibition. This implied that cupric phosphate could be responsible for the reduction of copper release by forming a protective layer.     

Corrosion of metals and alloys in molten glasses. Part 1: glass electrochemical properties and pure metal (Fe, Co, Ni, Cr) behaviours

Corrosion of pure metals Fe, Ni, Co, Cr in molten glass was studied at 1050 °C by electrochemical techniques and thickness losses measurements. These two techniques are in good agreement. The electrochemical apparatus was used to determine the formal potential of some redox couples, to identify the corrosion reactions and to evaluate the corrosion rates.Among tested metals, only chromium is a passivable material. The passivation is due to the formation of a chromium oxide (Cr₂O₃) protective layer at the glass/metal interface. Then superalloys used in molten glass must contain a high chromium level to resist to corrosion.     

Corrosion inhibition of mild steel in 1 M HCl solution by henna extract: A comparative study of the inhibition by henna and its constituents (Lawsone, Gallic acid, α-d-Glucose and Tannic acid)

The inhibitive action of henna extract (Lawsonia inermis) and its main constituents (lawsone, gallic acid, α-d-Glucose and tannic acid) on corrosion of mild steel in 1 M HCl solution was investigated through electrochemical techniques and surface analysis (SEM/EDS). Polarization measurements indicate that all the examined compounds act as a mixed inhibitor and inhibition efficiency increases with inhibitor concentration. Maximum inhibition efficiency (92.06%) is obtained at 1.2 g/l henna extract. Inhibition efficiency increases in the order: lawsone > henna extract > gallic acid > α-d-Glucose > tannic acid. Also, inhibition mechanism and thermodynamic parameters are discussed.