A study of the corrosion of aluminum alloy 2024-T3 under thin electrolyte layers

The corrosion of aluminum alloy 2024-T3 (AA2024-T3) under thin electrolyte layers was studied in 3.0 wt% sodium chloride solutions by cathodic polarization and electrochemical impedance spectroscopy (EIS) method. The cathodic polarization measurements show that, when the electrolyte layer is thicker than 200 μm, the oxygen reduction current is close to that of the bulk solution. But in the range of 200-100 μm, the oxygen reduction current is inversely proportional to the layer thickness, which shows that the oxygen diffusion through the electrolyte layer is the rate-determining step for the oxygen reduction process. In the range of 100 μm to about 58 μm, the oxygen reduction current is slightly decreased probably due to the formation of aluminum hydroxide or the change of the diffusion pattern from 2-dimensional diffusion to one-dimensional diffusion. The further decrease in electrolyte layer thickness increase the oxygen reduction current to some extent again, because the diffusion of oxygen plays more important role in thin electrolyte layers.The EIS measurements show that the corrosion is controlled by the cathodic oxygen reduction at the initial stage, showing the largest corrosion rate at the electrolyte layer thickness of 105 μm. But at the later stage of corrosion, the anodic process begin to affect the corrosion rates and the corrosion rates show a maximum at 170 μm, which may be the thickness where the corrosion changes from cathodic control to anodic control. The corrosion rate under the very thin electrolyte layer (62 μm in this study) is even smaller than that in bulk solution, this is due to that the anodic process is strongly inhibited.     

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.     

The kinetics of the corrosion of copper containing different amounts of oxygen in 1.7 M H2SO4

The rate of corrosion of rotating copper discs was measured as a function of the concentration of oxygen in metal. It was found that the catastrophic acceleration of the corrosion of the sample occurs at 3 × 10³ ppm of oxygen in metal. In the temperature range 5–75°C, the corrosion resulting from the presence of the oxygen in the metal occurs in the regime of activational control, and it is not influenced by the oxygen dissolved in the acid. The corrosion resulting from the oxygen depolarization occurs in the activational control regime in the temperature range 5–35°C, in the mixed kinetics regime in the range 45–55°C, and in the range 65–75°C in the diffusional regime with respect to the oxygen dissolved in the acid. The overall rate of corrosion of copper containing 8 × 10³ ppm of oxygen is about 20 times greater than the rate of corrosion of copper with oxygen depolarization.     

Simulation atmosphärischer Korrosion durch dünne Elektrolytfilme

Simulation of atmospheric corrosion by thin films of electrolyte A method for investigation on atmospherical corrosion with the aid of thin electrolyte films is described, the special feature of this being the exact adjustability of the corrosion determining parameters. The investigations on the influence of pollutants showed that small additions of sodium chloride and sulphur dioxide into the water film cause two different types of corrosion of electrolytic copper: uniform growth of layer thickness and/or lateral surface growth of the corrosion products. In the initial phase the uniform growth of layer thickness on electrolytic copper depends on t² (t = time), later on proportional on t. The investigation of the corrosion in dependence on the thickness of electrolyte film showed new results regarding the transition of the bulk-electrolytical to thin film electrolyte corrosion (atmospheric corrosion). At electrolytic copper transition from uniform growth of layer thickness to lateral surface growth comes off, when reaching a film thickness of approx. 100 μm. The electrolyte was distilled water with an addition of 0,01%SO₂. The corrosion intensity of grey cast iron GG 25 under a film of pure water passes through a wide maximum of film thickness between 300 and 20 μm, with a weakly marked minimum on 100 μm, the corrosion intensity is decreasing at thinner films. It is herewith demonstrated that also under conditions excluding largely the convective oxygen transfer other corrosion types and -intensities show up when the films are only thin enough. The comparison of the effect of two vapour inhibitors, having been dissolved directly in the electrolyte films (dicyclohexyl-ammoniumnitrite and one usual in the trade of unknown composition) in different concentrations showed on grey cast iron GG 25 the superiority of the latter one.     

Determination of instantaneous corrosion rates and runoff rates of copper from naturally patinated copper during continuous rain events

Instantaneous corrosion rates of naturally patinated copper of varying age (16 months, 138 and 145 years) have been determined during continuous rain events in the laboratory with electrochemical impedance spectroscopy using a two-electrode cell. The two-electrode cell was found to yield the same information in bulk rainwater as a conventional three-electrode cell.Relatively constant corrosion rates, between 0.2 and 0.6 μm/y, were determined for samples having a two-layer structure with an inner brownish layer of cuprous oxide and an outer greenish layer of basic copper salts (138, 145 years). Samples with cuprous oxide as the dominating phase of the patina (16 months) showed higher and somewhat increasing corrosion rates during a rain event (from 0.6 to 1.2 μm/y). During a continuous rain event, corrosion rates were found to be approximately 10 (brownish patina) and 25 times (greenish patina) lower than corresponding instantaneous runoff rates. The first flush phenomena of the runoff process, with an increased concentration during first flush and a relatively constant concentration during steady state, was indirectly seen as an increase in solution conductivity during the first rain volume followed by relative constant value. The contribution of the concentration in the first flush to the total annual runoff rate was significant for panels having a greenish layer (138, 145 years) whereas it was negligible for panels having a brownish layer (16 months).     

The effect of adatoms on the corrosion rate of copper

On the premises that corrosion is a surface process and adatoms modify the electronic states of the surface, the influence of Zn, Sn, S, I, F, Ta, Sb, Ti, Bi and Cr adatoms on the corrosion rate of copper was investigated. Adatoms were adsorbed at open-circuit from a solution containing 1.0×10⁻² mol l⁻¹ of the ions of the adatom element. The coverage of the adatoms at the surface was calculated by integration of the area under one of the peaks on the voltammogram of the copper electrode before and after dosing the electrode with the adatom. A significant difference in adsorbability of the adatoms at copper surface was observed. This difference was inter alia attributed to atomic size, crystallographic and kinetic effects. The surface properties were characterized by cyclic voltammetry, and for selected systems by SEM and electron microprobe. Corrosion of the surface in presence and in absence of the adatoms was followed by weight-loss method while surface oxidation, ‘surface corrosion’ was investigated by cyclic voltammetry and by electrochemical polarization techniques. The results showed that the nonmetals (F, S and I) markedly enhanced the rate of corrosion; Cr, Ta, Sb, Bi, Ti, Sn slightly enhanced the rate of corrosion of copper. Zinc, however, was the only element which decreased the rate of corrosion.     

Early stages of copper corrosion behaviour in a Tunisian soil

The early stages of copper corrosion in a Tunisian soil were studied using mass loss, surface analysis (optical microscopy, visible spectroscopy, IRTF and atomic force microscopy) and electrochemical characterizations (polarization curves and cyclic voltammetry). The corrosion rate dependence with immersion time was Δm = at^b. Two behaviours for the material surface were evidenced when varying the soil concentration and temperature. Then, the apparent kinetic constant, the soil reaction order and the apparent activation energy were calculated. Analytical and electrochemical characterizations showed that a rough patina layer was build up as a result of the interaction between soil and copper.     

Corrosion behaviour of copper under chloride-containing thin electrolyte layer

The corrosion behaviour of copper under chloride-containing thin electrolyte layers (TEL) was investigated using electrochemical impedance spectroscopy (EIS), cathodic polarization, linear polarization, SEM/EDS and XRD. The results indicate that the copper corrosion rate increases as TEL thickness decreases during the initial stages. After 192 h of immersion, the corrosion rate of copper under TEL in this order: 300 > 402 > 199 > bulk solution > 101 μm. The corrosion behaviour is uniform under TEL, and pitting is the primary corrosion type in the bulk solution. A corrosion model of the behaviour of copper under chloride-containing TEL is proposed.     

Laboratory scale investigation into the corrosion of copper in a sulphur-containing environment

The effect of temperature and gas composition on the corrosion rate and corrosion by-product of copper foil was studied by exposing it to sulphur (S₂), S₂ + hydrochloric acid (HCl) and hydrogen sulphide. The temperature was varied from 80 to 140 °C. Copper foil reacted with S₂ to form CuS, Cu₉S₈ and Cu_1.8S. Corrosion rates ranged from 9.6 μm/h at 110 °C to 0.5 μm/h at 140 °C. The presence of HCl caused pitting and enhanced the corrosion rate above 112 °C. Cu₂S formed when copper was exposed to hydrogen sulphide gas. Sulphide scale that formed was friable and non-adherent.     

Electrochemical corrosion behavior of bronze materials in an acid-containing simulated atmospheric environment

The present work investigates the corrosion behavior of bronze materials under thin electrolyte layers (TELs) in a simulated atmospheric environment containing formic and acetic acid by electrochemical measurements as well as surface characterization. The results show that the corrosion of bronze under TEL is significantly faster than that in the bulk solution, and the corrosion rate of bronze is the highest when the thickness of TEL is about 100 μm. Formic acid is observed to be more corrosive than acetic acid. Copper formate and copper acetate hydrate appear in the corrosion products formed on the surface of bronze, suggesting that the organic acid participates in the corrosion process of bronze materials in the simulated atmospheric environment.     

Galvanic coupling between copper and aluminium in a thin-layer cell

The Al/Cu coupling was investigated in a thin-layer cell formed by a large Cu electrode and an Al microelectrode embedded in an insulator placed above the Cu electrode. By using a scanning electrochemical microscope (SECM) the thickness of the thin layer was perfectly controlled with a precision in the micrometer range. A copper deposit on an electrochemical quartz crystal microbalance (EQCM) was also used as SECM substrate to quantify the copper dissolution rate. It was shown that such an experimental set-up allows to mimic the galvanic corrosion of intermetallic particles embedded in the aluminium matrix of the 2XXX series aluminium alloys. The combination of the SECM and the EQCM permitted the evaluation of the corrosion rate of copper at the corrosion potential of the 2024 Al alloy, whereas cyclic voltammetry performed on the SECM tip indicated the enrichment in Cu²⁺ ions in the thin electrolyte layer.     

Effects of alternating magnetic field on the corrosion rate and corrosion products of copper

The effects of alternating magnetic field on the corrosion morphologies, corrosion rate, and corrosion products of copper in 3.5% NaCl solution, sea water, and magnetized sea water were investigated using electrochemical test, scanning electron microscopy/energy dispersive analysis system of X-ray (SEM/EDAX), and X-ray diffraction (XRD). The results show that the corrosion rate of copper in magnetized sea water is minimal. Moreover, the surface of the specimen in magnetized sea water is uniform and compact as compared with those in 3.5% NaCl solution and sea water. The corrosion products of copper in magnetized sea water are mainly Cu2O and CuCl2. However, the corrosion products in sea water are CuCl, Cu2Cl(OH)3, and FeCl3·6H2O. The electrochemical corrosion mechanisms of copper in the three media were also discussed.     

Breakaway properties of film formed on copper and copper alloys in erosion–corrosion by mass transfer equation

Erosion–corrosion tests on copper and three types of copper alloys in a 1 wt% solution of CuCl₂ were carried out at various flow velocities using a jet‐in‐slit testing apparatus, which is capable of reproducing various hydrodynamic conditions. A damage profile of a specimen was developed using a surface roughness meter to evaluate locally occurring damage. The damage depth rate for copper, beryllium copper, and a 70/30 copper nickel alloy increased with increasing flow velocity, and suddenly increased at a certain velocity, which is called the breakaway velocity. The breakaway velocities at the central and disturbed part of a specimen were different for each sample, indicating that the hydrodynamic conditions of the flowing solution had an effect. The damage depth rate, calculated from the mass transfer equation, which involved mass transfer in the concentration diffusion layer and in the corrosion product film, could be fitted to the experimental data, suggesting that the mass transfer equation can be applied to the evaluation of erosion–corrosion damage. The corrosion product film was exponentially broken away at velocities higher than the breakaway velocity. The breakaway properties of the corrosion product film were confirmed to be different for each material, since the power of the exponential equation was different for each sample.     

Atmospheric corrosion monitoring of a weathering steel under an electrolyte film in cyclic wet–dry condition

Electrochemical Impedance Spectroscopy (EIS) and film thickness measurements have been employed to study the corrosion monitoring of steel under an electrolyte film in wet–dry cycles simulating a coastal atmosphere. The results indicate that within each cycle, the corrosion rate increases during drying process due to an increase in Cl⁻ concentration and an enhancement of oxygen diffusion by thinning out of the electrolyte. As corrosion process proceeds, the corrosion rate increases greatly and reaches a maximum. During subsequent corrosion stage, the corrosion rate decreases greatly and keeps at a low value due to the formation of a stable rust layer.     

Generation of nanostructured CuO by electrochemical method and its Zn–Ni–CuO composite thin films for corrosion protection

Nanocrystalline copper oxide (CuO) powder of varying sizes (22, 25, 28 and 36 nm) have been successfully synthesized by hybrid electrochemical method using aqueous sodium nitrate electrolyte with Cu electrodes under galvanostatic mode at room temperature. The as‐synthesized CuO sample was calcined for an hour at temperatures ranging from 60 to 900 °C. The crystallite size, morphology, and chemical state of the synthesized powders were characterized by powder XRD, XPS, SEM/EDAX, TEM, and UV–Vis spectral methods. The effect of calcination temperature on crystallite size and morphology was studied. The TEM result revealed that, the particles are hexagonal and the sizes are in 30–50 nm in diameter and 120–200 nm in length. The band gap values are 5.60 and 5.54 eV. The crystallite size increased with increase of calcination temperature. The CuO nanopowder is used to fabricate Zn–Ni–CuO composite thin films and its corrosion behaviour was analysed by Tafel extrapolation and electrochemical impedance spectroscopy. The results indicate that the Zn–Ni–CuO composite thin films provided good corrosion protection.     

Stress corrosion cracking of pure copper in dilute ammoniacal solutions

Studies of the stress corrosion cracking (SCC) of 99.999% copper and Cu-Zn alloys containing up to 10 wt%Zn in NH₄OH solution were made with varying concentrations (0.03–0.07 M) and temperatures (40–70°C). Stress corrosion cracking occurs on pure copper and all of the alloys under the condition in which thick tarnish film (Cu₂O oxide film) forms. The path of cracking is transgranular for pure copper and alloys containing < 1.3 wt%Zn, but intergranular for alloys containing > 1.3 wt%Zn. Crack propagation rates and times-to-failure estimated by the tarnish rupture theory, utilizing experimentally determined values of the fracture strain of film and the creep rate of specimens during SCC tests, are in good agreement with those observed under constant load.     

Direct measurement of corrosion inside iron crevices

Using visible crevices formed between 8 × 4 × 0.2 cm iron plates and 8 × 2.5 × 0.2 cm glass sheets, with widths of 100, 200 and 300 μm achieved by adhesive tapes of the appropriate thickness, drying kinetics were determined as a function of crevice width and environmental relative humidity. Determinations were also made of the corrosion rate inside the crevice by gravimetry, the aspect of the corrosion products by visual observation, and the morphology of attack by optical microscopy. The corrosion kinetics results indicate that dissolved oxygen in the electrolyte inside the crevice is renewed thousands of times over the course of several days.     

Determination of the corrosion rate of powder materials by electrochemical methods

The application of polarization and impedance measurements to determine the corrosion rate of porous materials and those infiltrated with copper, produced by powder metallurgy, in neutral chloride electrolyte is examined. The determination of the corrosion rate of porous powder materials per true surface area in view of their heterogeneity is described.     

Galvanic corrosion behaviors of Cu connected to Au on a printed circuit board in ammonia solution

During etching treatments of printed circuit board (PCB) with ammnioa solution, galvanic corrosion occurs between electrically connected gold and copper, and resulting in unexpected over-etching problems. Herein, we determine corrosion of galvanic coupled Cu to Au quantitatively in ammonia solutions, and evaluate factors influencing corrosion of galvanic coupled Cu to Au (i.e., area ratio of anode to cathode and stirring speed). The difference of the corrosion rate (Δi = i_{couple, (Cu-Au)}–i_{corr, Cu}) of Cu connected to Au (117 μA/cm²) and of single Cu (86 μA/cm²) infers the amount of over-etching of Cu resulting from galvanic corrosion in ammonia solution (Δi = 0.31 μA/cm²). As the stirring speed increases from 0 to 400 rpm, the corrosion rate of galvanic coupled Cu to Au increases from 36 to 191 μA/cm². Furthermore, we confirm that an increase in the area ratio (Au/Cu) from 0.5 to 25 results in a higher rate of corrosion of Cu connected to Au. The corrosion rate of galvanic coupled Cu to Au is approximately 20 times higher when the area ratio of Au to Cu is 25 (1360 μA/cm²) than when the ratio is 0.5 (67 μA/cm²).     

Tafel slopes used in monitoring of copper corrosion in a bentonite/groundwater environment

The harmonic analysis, the polarization resistance, and the noise resistance methods have been applied in an effort to monitor corrosion of pure copper in a bentonite/groundwater environment with commercially available equipment. Without the need to use a reference electrode, the first method supplies not only an estimate of the corrosion rate, but also estimates of Tafel slopes required by the other methods. The recorded corrosion rate is overestimated but to a varying degree. While the recorded corrosion rates for the first two methods give quite similar values far below 3 μm/year, the electrochemical noise resistance method gives considerably higher values.