Characterization of the copper/electrolyte interface on two copper conductors under high voltage

The effect of a high applied voltage up to 30 V between two copper conductors is investigated in a 0.05 mol L⁻¹ sodium chloride solution. It appears that the potential is mainly applied to the anode/electrolyte interface and that, after a fast decay, the overall current density reaches a constant value, which is independent of the applied potential. This “passive” behaviour is attributed to the formation of a copper(I) chloride layer at the surface of the anode that limits the dissolution rate of copper in the electrolyte. It is shown that electromigration of chloride ions trough the CuCl layer controls the overall anodic reaction.     

Influence of hydrolysis time on the structure and corrosion protective performance of (3-mercaptopropyl)triethoxysilane film on copper

Films of (3-mercaptopropyl)triethoxysilane with different hydrolysis time were formed on copper surface. To evaluate the influence of hydrolysis time on structures and corrosion resistance of these films, Fourier-transform infrared spectroscopy, polarization curves, cyclic voltammetry and electrochemical impedance spectroscopy tests were performed on covered and uncovered copper specimens. Results indicate that the optimum hydrolysis time is 48 h. The film obtained in this case shows the best corrosion resistance in 3.5% (w) NaCl solution.     

Inhibition of copper corrosion in sodium chloride solution by the self-assembled monolayer of sodium diethyldithiocarbamate

Sodium diethyldithiocarbamate (DDTC) self-assembled monolayer (SAM) on copper surface has been investigated by SERS and EDS and the results show that DDTC SAM is chemisorbed on copper surface by its S atoms with tilted orientation. Corrosion inhibition ability of DDTC SAM was measured in 3% NaCl solution using electrochemical methods. The impedance results indicate that the maximum inhibition efficiency of DDTC SAM can reach 99%. Quantum chemical calculations show that DDTC has relatively small ΔE between HOMO and LUMO and large negative charge in its two sulfur atoms, which facilitates the formation of a DDTC SAM on copper surface.     

Kinetic peculiarities of anodic dissolution of silver and Ag–Au alloys under the conditions of oxide formation

The kinetics of anodic dissolution of silver and Ag–Au alloys (X_Au = 0.1–30 at.% Au) in aqueous alkaline solution under the conditions of the formation of silver oxides has been examined. The techniques of cyclic voltammetry, chronoammetry, and photopotential measurements have been used. It was established that the anodic formation and cathodic reduction of Ag₂O on silver and alloys are controlled by migration in the oxide layer. Ag₂O oxide is an n-type semiconductor with an excess of silver atoms. Oxide layers formed on monocrystalline Ag(1 1 1) and Ag(1 1 0) are more stoichiometric than the layer formed on polycrystalline Ag.     

Film formation and surface growth on tin electrodes in bicarbonate solutions: an impedance spectroscopy study

The electrochemical behaviour of potentiodynamically formed thin anodic films of polycrystalline tin in aqueous sodium bicarbonate solutions (pH ≈ 8.3) were studied using cyclic voltammetry and electrochemical impedance spectroscopy. Different equivalent circuits corresponding to various potential regions were employed to account for the electrochemical processes taking place under each condition.     

The valence state of copper in anodic films formed on Al-1at.% Cu alloy

During anodising of Al-Cu alloys, copper species are incorporated into the anodic alumina film, where they migrate outward faster than Al³⁺ ions. In the present study of an Al-1at.% Cu alloy, the valence state of the incorporated copper species was investigated by X-ray photoelectron spectroscopy, revealing the presence of Cu²⁺ ions within the amorphous alumina film. However, extended X-ray irradiation led to reduction of units of CuO to Cu₂O, probably due mainly to interactions with electrons from the X-ray window of the instrument and photoelectrons from the specimen. The XPS analysis employed films formed on thin sputtering-deposited alloy/electropolished aluminium specimens. Such an approach enables sufficient concentrations of copper species to be developed in the anodic film for their ready detection.     

Kinetic peculiarities of anodic dissolution of copper and its gold alloys accompanied by the formation of insoluble Cu(I) products

The kinetics of anodic dissolution of Cu and Cu-Au alloys (0.1-30 at.% Au) in aqueous chloride-containing universal buffer mixture (pH 1.25-11.90) in the potential range of insoluble Cu(I) products formation has been examined using the technique of multicyclic voltammetry and chronoamperometry of stationary and rotating electrodes. After the formation of anodic film, mass transport controls the dissolution; the phase where the transport is localised depends on the nature of the film, pH of the solution and the alloy composition. The initial stage of CuCl formation on Cu and low-concentration Cu-Au alloys is controlled by 2D-nucleation.     

Effect of sulphide on the corrosion behaviour of AISI 316L stainless steel and its constituent elements in simulated Kraft digester conditions

The electrochemical behaviour of AISI 316L steel and its constituent metals in simulated Kraft digester white liquor at 170 °C has been studied by registering slow scan rate voltammograms and impedance spectra at the corrosion potential. Interpretation of the results in terms of two approaches - the Mixed-Conduction Model for passive films and a two-step dissolution reaction - allowed for the estimation of corrosion currents and polarisation resistances as depending on the material and electrolyte medium. Tentative conclusions on the effect of sulphur-containing species in the white liquor on the corrosion mechanism of the studied materials are drawn.     

Investigation of the inhibition effect of indole-3-carboxylic acid on the copper corrosion in 0.5 M H2SO4

Inhibition of the copper corrosion by means of indole-3-carboxylic acid (ICA), was studied in 0.5 M H₂SO₄ solutions in the temperature range from 25 °C to 55 °C using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results obtained from the both measurement techniques revealed good inhibitor efficiency in the studied concentration range. Nyquist plots showed depressed semicircles with their centre below real axis. Moreover, the impedance spectra in the case of both non inhibited solutions and inhibited ones by means of lower inhibitor concentrations exhibited Warburg impedance. The adsorption behaviour of ICA followed Langmuir’s isotherm.     

Poly(N-methylaniline) coatings on stainless steel by electropolymerization

Poly(N-methylaniline) (PNMA) coatings have been electropolymerized on 304 stainless steel alloy by potentiodynamic, galvanostatic and potentiostatic synthesis techniques from aqueous solutions of 0.1 M N-methylaniline (NMA) and 0.3 M oxalic acid. Characterization of PNMA coatings was carried out by cyclic voltammetry, UV-Vis and FTIR spectroscopy techniques. Corrosion behavior of PNMA coated stainless steel electrodes was investigated using linear anodic potentiodynamic polarization, Tafel test, chronoamperometry and electrochemical impedance spectroscopy (EIS) techniques in 0.5 M aqueous HCl solutions. Corrosion test results showed that PNMA coatings possessed protection to uncoated stainless steel against corrosion.     

Effect of vegetal tannin on anodic copper dissolution in chloride solutions

The corrosion inhibition of copper in a 0.1 M NaCl solution in the presence of vegetal tannin using potentiodynamic techniques was studied. The tannin was extracted from Takaout galls (Tamarix articulata). The gallic acid has been used as a representative of the tannin species. The tannin are anodic inhibitors. The inhibition efficiency of the tannin evaluated from anodic polarization curves and impedance measurements is about 93.2% for a tannin concentration of 2 g/l. We noted that the presence of tannin changes the mechanism of copper dissolution in a 0.1 M NaCl solution. Microscopic scanning studies of the surface state revealed the formation of corrosion layer products. The impedance investigation allows the explanation of the inhibition process.     

The effect of various halide ions on the passivity of Cu, Zn and Cu-xZn alloys in borate buffer

Cu and Zn metals and four of their alloys, Cu-10Zn, Cu-20Zn, Cu-30Zn and Cu-40Zn, were studied in borate buffer, pH = 9.2, in the presence of the halides, NaF, NaCl, NaBr and NaI. Electrochemical polarization and SEM/EDS methods were used in the study. The mechanism of corrosion of copper and copper alloys induced by iodide ions differed fundamentally from that induced by other halide ions. Iodide ions promote the general type of corrosion during which very slowly soluble CuI is formed. F⁻, Cl⁻ and Br⁻ ions promote localized corrosion attack. All halide ions induce localized corrosion on the passive layer on zinc. The breakdown potentials of Cu, Zn and four Cu-xZn alloys were measured as a function of concentration and type of halide ions.     

Temperature effect in the corrosion resistance of Ni-Fe-Cr alloy in chloride medium

The corrosion susceptibility of alloy 33 in 0.5 mol/L sodium sulphate solutions containing or not 0.1 mol/L sodium chloride was tested at three different temperatures: 22 °C, 40 °C and 60 °C. Electrochemical studies were performed using corrosion potential measurements (E_corr) as well as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Corrosion potential measurements showed that alloy 33 was passivated by a previously air formed film which was not destroyed during immersion in both solutions. No corrosion was observed during these tests although the temperature affected the film. Potentiodynamic polarization experiments showed that at high anodic potentials the previous film was broken up, and localized corrosion occurred in both solutions and at the three temperatures tested. Electrochemical impedance spectroscopy tests confirmed the presence of a stable passive film on the alloy surface at open circuit potential. Mott-Schottky analysis indicated that the passive film is an n-type semiconductor due to the presence of point defects of donor species, such as oxygen vacancies and interstitial metallic cations. As the potential increases the Cr(III) present in the barrier layer oxidizes producing Cr(VI) soluble species. The dissolution creates metallic cation vacancies that are acceptor species and the film changes from n-type to p-type semiconductor. The passive film rupture and the following localized attack are related to the drastic oxidative dissolution of the film at high anodic potentials, independent of its p-nature, chloride presence or increased temperature.     

Photocurrent and capacitance investigations into the nature of the passive films on austenitic stainless steels

Photocurrent and capacitance measurements of semiconductor passive films formed on metals and alloys can be used to study the electronic properties and reveal indirect information about structure and composition. The current work used these techniques to investigate the electronic properties of the passive films formed on three austenitic stainless steels, types 304L, 316L and 254SMO, in borate. Evidence was found for the existence of a large number of localised mid bandgap states, consistent with amorphous oxides. However, the flat-band potentials of the austenitic stainless steel passive films were found to be independent of both composition and measuring frequency. The most credible explanation for the bandgap values determined from photocurrent measurements is that the passive films are formed as dual layers, iron oxide outer layer and chromium oxide inner layer. This model does not need to evoke the potential dependent bandgaps used by previous authors.     

Corrosion control of copper in 3.5 wt.% NaCl Solution by Domperidone: Experimental and Theoretical Study

Inhibition of copper corrosion in 3.5 wt.% NaCl solution by domperidone was investigated by weight loss, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The experimental results revealed that domperidone was an anodic inhibitor with a maximum achievable inhibition efficiency of 94.2%. The results of SEM and AFM studies further confirmed the inhibition action of domperidone. Quantum chemical calculation and the molecular dynamics (MD) simulation showed that the domperidone molecule could be adsorbed on copper surface through the imidazolidinone ring, benzene ring and N atom of hexaheterocyclic. Adsorption of domperidone was found to follow the Langmuir adsorption isotherm.     

Kinetics of H2O2 reaction with oxide films on carbon steel

The nature of carbon steel surfaces in 0.01 M borate solutions (pH 10.6) have been characterized using a range of electrochemical techniques and ex situ analyses such as Raman and Auger spectroscopy. Their subsequent behaviour on exposure to 10⁻³ M H₂O₂-containing solutions has also been studied. The anodically oxidized carbon steel surfaces have been characterized according to three regions: (I) the potential range <−0.5 V (vs SCE), when the surface is active and covered by Fe^II/Fe^III oxide/hydroxide; (II) the potential range −0.5 V to 0.0 V when the surface is passivated by an outer layer of Fe^III oxide/hydroxide over the inner layer of Fe^II/Fe^III oxide/hydroxide; and (III) potentials >0 V when further growth of the underlying layer appears to lead to minor film breakdown/restructuring. The addition of H₂O₂ to films grown in the passive region or above (II and III) leads initially to a degradation of the outer layer allowing increased growth of the inner layer. Subsequently, the outer passivating layer is repaired and passivity re-established. These changes appear to be confirmed by Raman spectroscopy.     

Copper–nickel alloys modified with thin surface films: Corrosion behaviour in the presence of chloride ions

A strong influence of the Ni content in on the barrier properties of the surface films, spontaneously formed on Cu–Ni alloys (containing 10–40 at.% of Ni) in a slightly alkaline NaCl solution or previously produced by forming bis(diethyldithiocarbamato)Cu(II) and Ni(II) surface complexes, were studied under stagnant and solution impinging conditions using polarization and EIS methods. An unexpected behaviour that the corrosion resistivity of alloys with x(Ni) ? 20 at.% is lower than that of the Cu–10Ni alloy was explained using solid-state processes within the surface films and enhanced electronic conductivity of the surface film formed on the Cu–10Ni alloy.     

The investigation of synergistic inhibition effect of rhodanine and iodide ion on the corrosion of copper in sulphuric acid solution

The synergistic inhibition effect of rhodanine (Rdn) and iodide ion on the corrosion of copper in 0.5 M H₂SO₄ solution was studied using electrochemical techniques. The surface morphologies of the substrates were examined by scanning electron microscopy (SEM). Elemental analysis of electrode surface exposed to test solution was determined by energy dispersive X-ray spectroscopy (EDX). It was found that Rdn provided satisfactory inhibition on the corrosion of copper. Moreover, its inhibition efficiency further increased in the presence of iodide ions due to synergistic effect. Finally, a mechanism of inhibition is proposed and discussed.     

The influence of pH value on the efficiency of imidazole based corrosion inhibitors of copper

The aim of this work is to establish the correlation between the solution pH and the inhibiting efficiency of two imidazole compounds (4-methyl-1-phenyl imidazole and 4-methyl-1-(p-tolyl) imidazole) in protection of copper from corrosion in chloride media.It was found that the inhibiting efficiency of both studied imidazoles enhances with the increase of the solution pH value, from about 20% in 0.5 M HCl to 92% in 0.5 M NaCl. This improvement was ascribed to stronger adsorption of neutral imidazole molecule, which can be expected at higher pH values, than that of the protonated imidazole cation, which may be expected in acid solutions.     

Influence of molybdate species on the tartaric acid/sulphuric acid anodic films grown on AA2024 T3 aerospace alloy

AA2024 T3 alloy specimens have been anodised in tartaric acid/sulphuric media and tartaric acid/sulphuric media containing sodium molybdate; molybdate species were added to the anodising bath to enhance further the protection provided by the porous anodic film developed over the macroscopic alloy surface. Morphological characterisation of the anodic films formed in both electrolytes was undertaken using scanning electron and transmission electron microscopies; the chemical compositions of the films were determined by Rutherford backscattering spectroscopy that was complemented by elemental depth profiling using rf-glow discharge optical emission spectrometry. The electrochemical behaviour was evaluated using potentiodynamic polarisations and electrochemical impedance spectroscopy; the corrosion performance was examined after salt spray testing. The porous anodic film morphology was little influenced by the addition of molybdate salt, although thinner films were generated in its presence. Chemical composition of the anodic film was roughly similar; however, addition of sodium molybdate in the anodizing bath resulted in residues of molybdate species in the porous skeleton and improved corrosion resistance measured by electrochemical techniques that was confirmed by salt spray testing.