Corrosion behavior of copper in extremely harsh marine atmosphere in Nansha Islands,China

The corrosion behavior of pure copper exposed to the atmosphere of Nansha Islands for 21 months was studied by mass loss method, composition analysis, morphology observation and electrochemical measurements. The results showed that the average corrosion rate of copper exposed for one year was approximately 7.85 μm/a, implying that Nansha Islands was classified as a corrosion category of CX. The structure and properties of the corrosion product layer generated on the front and back sides of the exposed sample differed significantly. The inner corrosion product layer (Cu₂O) on the front side was relatively thick and dense, whereas the outer product layer (Cu₂Cl(OH)₃) was extremely thin. However, the outer product layer on the back side was thicker than the inner layer. Electrochemical measurements indicated that the protection afforded by the corrosion product layer on the front side was improved gradually, while that on the back side was deteriorated.     

7A04铝合金在海洋大气环境中初期腐蚀的电化学特性

通过盐雾腐蚀试验模拟研究7A04铝合金在海洋大气环境中的腐蚀初期规律,采用电化学交流阻抗测试和扫描Kelvin探针技术,研究7A04铝合金在初期腐蚀过程中的电化学行为.结果表明:Cl-对铝合金腐蚀有显著的加速作用,盐雾试验初期表面出现点蚀坑;随盐雾时间增长,点蚀相互连接并扩展,电化学反应阻抗下降.扫描开尔文探针测试结果表明:随腐蚀的不断进行,金属表面阴极区和阳极区不断发生变化,呈现局部腐蚀的特征,表面电位也随时间逐渐升高,阴极区和阳极区逐渐变得明显,腐蚀反应处于不断加速过程.     

Modelling sea-salt transport and deposition in marine atmosphere zone - A tool for corrosion studies

Atmospheric corrosion of metals and corrosion of reinforcements in concrete structures are influenced by salt concentration of marine aerosol inland. This work presents a model that represents marine aerosol behaviour in marine atmosphere zone. The model has the distance from the sea and wind speed as the major variables and takes into account changes in marine aerosol due to settlement of salts when being transported inland. The proposed equations M=M₀e^{(vdep₀/αh)[e(-αx/v)-1]}, D=D₀e^{(vdep₀/αh)[e(-αx/v)-1]} show good consistency with literature data and well represent the results obtained. This model can be a useful tool to indicate the salinity level expected at different distances from sea in marine atmosphere zone.     

Effect of the exposure angle in the corrosion rate of plain carbon steel in a marine atmosphere

This investigation aims to analyse the effect of the exposure angle on the corrosion rate of mild steel. Test samples were exposed to a marine environment at 0°, 30°, 45° and 90° inclination. To determine the effects of contaminants on the protective characteristics of the rusts, Cl and SO₂ contents in the atmosphere as well as SEM-EDX analyses and polarisation curves on the weathered samples were performed. Results demonstrated that the exposure angle influences the corrosion rate, as also the morphology of the rust, but with no effect on rust composition.     

Corrosion in artificial defects. I: Development of corrosion

Artificial defects (slots) were milled through a polyurethane topcoat and chromate-inhibited epoxy polyamide primer to the underlying aluminium alloy 2024-T3. The slots were then exposed to neutral salt spray (NSS) for up to 16 days. Prior to and after exposure, the slots were examined using scanning electron microscopy with energy dispersive X-ray analysis (SEM/EDS) and Raman spectroscopy. The milling process generated features on the surface not seen on polished surfaces, including smearing of the matrix alloy and fragmentation of Cu-Fe-Mn-Al intermetallic particles. It was found that the smears and S-phase particles acted as sites for the initiation of corrosion, which eventually developed more generally across the surface.     

Mechanistic studies of corrosion product flaking on copper and copper-based alloys in marine environments

The mechanism of corrosion product flaking on bare copper sheet and three copper-based alloys in chloride rich environments has been explored through field and laboratory exposures. The tendency for flaking is much more pronounced on Cu and Cu–4 wt%Sn than on Cu–15 wt%Zn and Cu–5 wt%Al–5 wt%Zn. This difference is explained by the initial formation of zinc and zinc–aluminum hydroxycarbonates on Cu15Zn and Cu5Al5Zn, which delays the formation of CuCl, a precursor of Cu₂(OH)₃Cl. As a result, the observed volume expansion during transformation of CuCl to Cu₂(OH)₃Cl, and concomitant corrosion product flaking, is less severe on Cu15Zn and Cu5Al5Zn than on Cu and Cu4Sn.     

Atmospheric corrosion behaviour of 30CrMnSiA high-strength steel in rural,industrial and marine atmosphere environments

The atmospheric corrosion behaviour of 30CrMnSiA high-strength steel exposed in rural, industrial and marine atmosphere environments in China for 60 months was investigated in virtue of the weight loss, X-ray diffractometer (XRD), scanning electron microscope (SEM) and grey relational analysis. The results showed that 30CrMnSiA high-strength steel exhibited the highest corrosion susceptibility and the lowest corrosion susceptibility in marine atmosphere environment and rural atmosphere environment, respectively. Lepidocrocite and goethite were found as the major constituents of the rust layer in three types of atmosphere environments, and akaganeite was also detected in marine atmosphere environment. The rust layer exhibited the tendency of flaking away from the substrate and becoming dense in marine atmosphere environment and rural atmosphere environment, respectively. Grey relational analysis demonstrated that, among a variety of environmental factors, the airborne sea-salt was the primary factor influencing the atmospheric corrosion of 30CrMnSiA high-strength steel.     

Corrosion of aluminium in copper-aluminium couples under a marine environment: Influence of polyaniline deposited onto copper

In this study, we examined how aluminium corrosion in Al-Cu/PANI galvanic couples in a marine environment is influenced by deposition of polyaniline (PANI) on copper. Polarization curves and immersion assays in 0.1 M NaCl were performed. The morphologies of etched Al and corrosion products were observed by SEM, and the Al ions in solution were quantified by atomic absorption spectroscopy. A reduction in aluminium damage due to galvanic corrosion was observed as a result of decreased effective area for the oxygen reduction reaction on Cu/PANI electrode. Furthermore, an electrochemical reduction of PANI from leucoemeraldine to emeraldine base is proposed.     

Stress Corrosion Cracking of Inconel 600 in aqueous solutions at elevated temperature part I: Initiation and inhibition of corrosion cracking process

The study reported here has been designed to determine the influencing effect of sulphate ions on chloride induced crack initiation of Inconel 600 using compact tension (CT) samples in chloride containing aqueous solutions at elevated temperature up to 250°. The results show that sulphate ions retard the effect of chloride ions on crack initiation in hot water up to 250°. Intergranular stress corrosion cracking (IGSCC) occurs in both chloride solution and in chloride solution with relatively low concentration of sulphate ions. The mode of cracking changes from brittle to ductile failure due to the influence of inhibiting concentration of sulphate. The results are interpreted in the light of repassivation-dissolution controlled mechanism which is the predominant mechanism. The inhibiting effect of sulphate ions on the initiation of corrosion cracking is attributed to the repassivation and the formation of Fe-Cr-spinel oxide layer which is stable also at higher temperature.     

Corrosion of carbon steel during cyclical exposure to wet elemental sulphur and the atmosphere

The corrosion of carbon steel during cyclical exposure to wet elemental sulphur (four days) and the atmosphere (six days) has been investigated. The integral corrosion rate is found to decrease with successive cycles, thereby demonstrating that oxidation of the sulphide film confers protection to the underlying steel.     

Long term corrosion behaviour of copper in soil: A study of archaeological analogues

The long term corrosion behaviour of copper in soil environment has been addressed by studying two archaeological copper samples. The microstructures of the material of construction of a Chalcolithic (2350BC‐1800BC) copper chisel from Balathal and an OCP period (2650BC‐800BC) Cu anthropomorphic object have been first characterized by microscopy and the features understood by stereological methods. The equiaxed grain size, coring effects in the grains and the relatively soft matrix of the OCP copper object indicated that it was manufactured by casting. The deformed grains near the surfaces and variation in the microhardness of the sample at different points suggests that the Chalcolithic copper chisel was processed by cold deformation after casting of the square cross section chisel. The surface patina on the two archaelogical copper objects has been characterized by X‐ray diffraction. In the case of OCP copper, the green surface patina was analyzed as a mixture composed mainly of cuprite, and minor amounts of malachite and brochantite. In the case of Chalcolithic copper, the patina was composed of sulfates and oxysulfates in the outer layers while the inner layers were rich in copper oxides. The electrochemical behaviour of both the archaeololgical coppers has been characterized and compared with that of a modern Cu sample by potentiodynamic polarization studies. The corrosion rate, determined by Tafel extrapolation technique in 3.5% NaCl solution, of Chalcolithic Cu was only marginally higher than that of modern and OCP Cu. The higher rates of corrosion in case of archaeological coppers have been attributed to the presence of second phase sulfide inclusions.     

On size effect of rate of corrosion of copper nanowire ensemble: Part 2. Size effect of rate of corrosion of copper in pyrophosphate solution

The corrosion of specimens of copper produced by electroplating on disc electrodes 10–500 μm in diameter from a pyrophosphate electrolyte is studied in this electrolyte (without added copper ions) using polarization curve measurements. It is found that the rate of corrosion of the microelectrodes with a radius of 5 μm is eight times higher than that of the microelectrodes with a radius of 25 μm; the measured rate of corrosion remains unchanged when varying the radius of the microelectrode in a range of 25–250 μm. It is shown that the process under investigation is corrosion with oxygen depolarization; the rate of reduction (of dissolved oxygen) increases eightfold when varying the radius of the microelectrode in a range of 5–25 μm. The experimental results are confirmed by the calculations of diffusion currents for the microelectrodes, which show that the size effect, i.e., an increase in the diffusion current density with decreasing area of the electrode surface, should be observed for electrodes with a radius less than 20–30 μm.     

Corrosion of iron archaeological artefacts in soil: characterisation of the corrosion system

This paper presents a study made on 40 iron archaeological artefacts buried in soil during several centuries. Samples were taken with the adhering soil and cross-sections were made. The used characterisation techniques are optical and electronic microscopies, EDS coupled to SEM, EPMA, micro-XRD under synchrotron radiation, micro-Raman spectrometry. A specific vocabulary is proposed to describe the corrosion layout. The most identified corrosion layout is made of several ten micrometers zones of magnetite and/or maghemite embedded in a goethite matrix. A corrosion mechanism is proposed in order to explain this profile. When the soil water contains more chlorine or carbonates, some specific corrosion product appear as akaganeite, oxychlorides and siderite.     

The size effect of the corrosion rate of a copper nanowire array. Part I: The corrosion potential variation

In obtaining a copper nanowire array by pulse template-assisted electrodeposition from a pyrophosphate electrolyte, during a long pause, the electrodeposited metal undergoes corrosion. Measurements of the corrosion potentials have shown that the corrosion rate of these materials in different corrosion environments depends on the pore size. The size effect of the corrosion rate can be accounted for by diffusion limitations of the electrode process of one of the conjugated stages, i.e., metal anodic dissolution or oxidant reduction.     

Astrakhan–Mangyshlak Water Main: Corrosion State of the Inner Surface, and Methods for Its Corrosion Protection. Part III. The Effects of KW2353 Inhibitor. Part IV. Microbiological Corrosion

It is inadmissible to employ the inhibitors of polyphosphate type, including KW/2353, for the corrosion protection of the inner surface of long-distance water mains. When becoming deficient due to its exhaustion, the inhibitor aggravates the localized corrosion. On the other hand, in sufficient concentration, it facilitates microbial corrosion, serving as a nutrient for microorganisms. The optimum method for the corrosion protection of the steel equipment contacting water media consists in their deoxygenation. Complex investigations, including corrosion-elecrochemical, physical and analytical tests, are necessary to predict both the rate and character of the corrosion of engineering equipment in contact with such media; the weighing procedures may be disinformative.     

Aerobic marine bacteria and the corrosion of carbon steel in sea-water

Comparisons have been made of corrosion rates calculated from polarization measurements of 1016 carbon steel specimens exposed to aerated sea-water drawn fresh from a local tidal channel and water from the same source, but Millipore filtered to remove living microbiota. No significant differences were found in the corrosion rates in the two environments. Aerobic bacteria capable of forming mucusoid material on sea-water plate count agar were obtained from the oxides on the surface of carbon steel exposed to untreated sea-water, but no coherent “slime film” was observed by dye stain, light microscopy, or scanning electron microscopy. Simulated “slimed” specimens showed significantly lower calculated corrosion rates. Scanning electron micrographs of oxide accumulations are shown.     

A new interpretation of the corrosion loss processes for weathering steels in marine atmospheres

Most available data sets for the long-term corrosion loss of various grades of weathering steel exposed to marine atmospheric environments are demonstrated to be consistent with the multi-phase corrosion model previously proposed for steels exposed to marine environments. This means that the early corrosion of weathering steels by oxidation is gradually inhibited by the build-up of corrosion products. These produce anoxic and sub-oxic conditions that may permit microbiological activity to govern the longer-term corrosion loss process. This new interpretation for the long-term corrosion of weathering steels may have implications for the design of such steels.     

A comparison between the corrosion behavior of nanostructured copper thin films deposited on oxidized silicon and copper sheet in alkaline media

Copper thin films were deposited on oxidized silicon at a substrate temperature of 70 °C and 150 °C using EB-PVD technique. The morphology and crystal orientation of the deposited film were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. Corrosion behavior of films was studied through electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, immersion test, and cathodic chronopotentiography. Additionally, the crystalline structure of corroded samples immediately after polarization was examined by XRD. Corrosion current density for copper deposits was higher than copper sheet by polarization tests, while the data obtained by the EIS technique emphasized higher corrosion current density for copper sheet. However there was a conflict between polarization and EIS data, the other results obtained by immersion and cathodic chronopotentiography tests proved that the corrosion resistance of copper deposits was higher than copper sheet in the same alkaline media, which can be attributed to chemical composition and higher thickness of the passive layer formed on copper deposits. On the other hand, breakdown potential (E_bp) for copper sheet was about 0.3 V_SCE, while a distinct E_bp was not found for copper deposits. This was a sign of higher stability of the passive layer formed on copper deposits. The XRD patterns of samples immediately after polarization showed a higher content of Cu(OH)₂ on copper deposits in comparison with copper sheet. The stable morphology formed on the surface of copper after polarization was monoclinic CuO, which is assumed to have a significant effect on copper protection in alkaline media. This morphology was more compact on copper deposits in comparison with copper sheet. This was due to higher ability of deposits to react with hydroxyl ions.     

Comparison of corrosion behaviour of zinc in NaCl and in NaOH solutions. Part I: Corrosion layer characterization

The corrosion layer formed on zinc sample in 0.6 M NaCl and 0.5 M NaOH solution under ambient conditions has been investigated. The corrosion layer morphology was analyzed using scanning electron microscopy (SEM). X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to characterize the corrosion products of zinc. The thickness evolution of the corrosion layer was investigated by glow discharge optical emission spectroscopy (GDEOS). The corrosion layer formed in 0.5 M NaOH solution appeared more compact than that formed in 0.6 M NaCl solution. Zinc hydroxide chloride (Zn₅(OH)₈Cl₂·2H₂O) and zinc hydroxide carbonate (Zn₅(CO₃)₂(OH)₆) were formed on zinc surface in 0.6 M NaCl solution while in 0.5 M NaOH solution, zinc oxide (ZnO), zinc hydroxide (Zn(OH)₂) and zinc hydroxide carbonate (Zn₅(OH)₆(CO₃)₂·H₂O) were detected. Probable mechanisms of zinc corrosion products formation are presented.