Corrosion and corrosion inhibition of Cu-20%Fe alloy in sodium chloride solution

The electrochemical behavior of copper (Cu), iron (Fe) and Cu-20%Fe alloy was investigated in 1.0 M sodium chloride solution of pH 2. The effect of thiourea (TU) addition on the corrosion rate of the Cu-20%Fe electrode was also studied. Open-circuit potential measurements (OCP), polarization and electrochemical impedance spectroscopy (EIS) were used. The results showed that the corrosion rates of the three electrodes follow the sequence: Cu < Cu-20%Fe < Fe. Potentiostatic polarization of the Cu-20%Fe electrode in the range −0.70 V to −0.45 V (SCE), showed that iron dissolves selectively from the Cu-20%Fe electrode surface and the rate of the selective dissolution reaction depends on the applied potential. At anodic potential of −0.45 V, thiourea molecules adsorb at the alloy surface according to the Langmuir adsorption isotherm. Increasing thiourea concentration (up to 5 mM), decreases the selective dissolution reaction and the inhibition efficiency η reach 91%. At [TU] > 5 mM, the dissolution rate of the Cu-20%Fe electrode increases due to formation of soluble thiourea complexes. At cathodic (−0.6 V), the inhibition efficiency of thiourea decreases markedly owing to a decrease of the rate of the selective dissolution reaction and/or desorption of thiourea molecules. The results indicated that thiourea acts mainly as inhibitor of the selective dissolution reaction of the Cu-20%Fe electrode in chloride solution.     

Effect of nitrite in corrosion of reinforcing steel in neutral and acid solutions simulating the electrolytic environments of micropores of concrete in the propagation period

Inhibitors in concrete are usually used to be effective in alkaline or neutral solutions, however, when corroding by chlorides, there is a local acidification and therefore it is necessary to study the effect of the inhibitor in acid pH values. Measurements of the corrosion rate of corrugated steel bars have been carried out in solutions simulating electrolytic chloride environments in the micropores of concrete in the propagation period. It has been studied the effect of sodium nitrite as a corrosion inhibitor when added to the mentioned solutions. The solutions considered consisted of sodium chloride for neutral condition and ferrous chloride for acid condition. This is the soluble compound produced during the corrosion of steel as a result of chloride attack. Comparison of the results of polarization resistance with gravimetrically determined weight losses are presented. Also, results of electrochemical impedance spectroscopy are presented here. It has not been observed a significative improvement in using nitrite as inhibiting agent in these systems. The corrosion seems to be related to the [Cl⁻]/[OH⁻] ratio in three different regions of pH identified from acid to alkaline pH values.     

Evaluation of the corrosion protection behaviour of poly(neutral red) films on passivated copper

The corrosion protection behaviour of poly(neutral red) (PNR) films on copper electrodes has been investigated using open circuit measurements, Tafel plots and electrochemical impedance spectroscopy. Pure copper electrodes were initially passivated in sodium oxalate, salicylate or hydrogen carbonate solution, to inhibit copper dissolution at potentials where neutral red monomer oxidation occurs, before its electropolymerization by potential cycling. The corrosion inhibition by these films was tested in 0.10 M KCl solution. It was found that, after long immersion times (96 h), the best protection efficiency was with PNR films formed on copper passivated in oxalate solution.     

Inhibitive effect of sodium eperuate on zinc corrosion in alkaline solutions

The effect of sodium eperuate prepared from Wallaba (Eperua falcata Aubl) extract on zinc corrosion was investigated in alkaline solutions with chloride ions (i.e., simulated concrete pore solutions) by using electrochemical techniques. Sodium eperuate inhibits the corrosion of zinc in 0.1 M NaCl solutions with pH 9.6. As its concentration increases to 1 g/L, the inhibition efficiency reaches approximately 92%. In alkaline solutions with pH 12.6, sodium eperuate has no adverse effect on passivity of zinc, and retards the chloride attack. These suggest that sodium eperuate is an effective inhibitor for the protection of zinc in alkaline environments.     

Modelling of phosphate inhibition of copper corrosion in aqueous chloride and sulphate media

Mathematical models were built to predict sodium phosphate inhibition of copper corrosion in aqueous chloride and sulphate media. SEM-EDXS and AFM were used to characterize material surfaces without and with inorganic salt addition. Inhibitor efficiency was compared with that exhibited by benzotriazole.     

Inhibition Effect of 2,4,6-Trimercapto-1,3,5-triazine Self-Assembled Monolayers on Copper Corrosion in NaCl Solution

2,4,6-Trimercapto-1,3,5-triazine (TMTA) was self-assembled on copper surface by a simple method and the resulting self-assembled monolayers (SAMs) were characterized by FTIR and contact angle. It was found that TMTA dissolved in aqueous solution could be adsorbed rapidly on the copper surface and yielded a hydrophilic surface. The inhibition effect of TMTA SAMs on copper corrosion in 0.5 M NaCl solution was investigated through potentiodynamic polarization curves and electrochemical impedance spectroscopy. Results indicated that TMTA SAMs acted as a mixed type corrosion inhibitor with predominant control of cathodic reaction. The inhibition efficiency increased with increasing assembly time but decreased to some extent with increasing concentration of chloride ions. Immersion test revealed the SAMs could keep good stability and durability in 0.5 M NaCl solution. From the experimental and theoretical study, the mechanisms of TMTA SAMs formation and corrosion protection for copper were discussed.     

Studies on corrosion inhibition of copper by alkanethiol SAMs prepared in aqueous micellar solution

The character of 1‐dodecanethiol (DT) self‐assembled monolayers (SAMs) formed on copper surface in aqueous micellar solution is investigated by means of contact angle measurement, electrochemical impedance spectroscopy (EIS), and polarization curves. The contact angle measurement shows that the SAMs formed in aqueous micellar solution are oriented and compact. According to the electrochemical measurements, it is found that both the concentration of DT and temperature can significantly affect the property of SAMs. The DT SAMs can prevent the corrosion of copper in chloride‐containing solution effectively because the inhibition efficiency can reach 99.59% at the DT concentration of 10^?2 M . The adsorption of DT in aqueous micellar solution obeys to the Langmuir adsorption isotherm, and the value of the free energy of adsorption calculated indicates that the adsorption of DT molecule is a spontaneous process and a typical of chemical adsorption.     

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.     

Environmental factors affecting pitting corrosion of type 304 stainless steel investigated by electrochemical noise measurements under potentiostatic control

Electrochemical noise measurements on anodically polarised type 304 stainless steel surfaces in contact with buffer solutions of neutral pH were performed to study the effect of chloride ions in the nucleation of pitting corrosion. Passive layer stability and susceptibility to pitting corrosion after pickling and passivation at different environmental conditions were also investigated by means of electrochemical current noise measurements under cathodic and anodic polarisation. According to the obtained experimental results pits nucleate independently on the presence of chloride ions. It has been also shown that protectiveness of stainless steel surfaces after pickling strongly depends on the relative humidity of the environment in which the surface is subsequently passivated.     

The influence of adenine on corrosion of copper in chloride solutions

The influence of the concentration of adenine (AD) on the corrosion and the spontaneous dissolution of copper in 1.0 M NaCl solutions of pH 6.8 was studied. The investigations involved electrochemical polarization methods as well as weight loss measurements, quartz crystal microbalance (QCM) techniques and scanning electron microscopy (SEM). The inhibition efficiency increases with an increase in the concentration of AD. An adherent layer of inhibitor is postulated to account for the protective effect. The adsorption of adenine has been found to occur on the surface of copper according to the Langmuir isotherm. The values of standard free energies of adsorption suggest chemical adsorption of AD on copper surface. The use of adenine can effectively prevent various new installations made of copper and exposed to the action of aqueous solutions of chlorides from corrosion damage.     

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.     

Effect of molybdate post-sealing on the corrosion resistance of zinc phosphate coatings on hot-dip galvanized steel

The technique of post-sealing the phosphated hot-dip galvanized (HDG) steel with molybdate solution was addressed. The composition and corrosion resistance of the improved phosphate coatings were investigated by SEM, EDS, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) measurements, and neutral salt spray (NSS) test. The results showed that molybdate films were formed in the pores of phosphate coatings, and the compact and complete composite coatings composed of phosphate coatings and molybdate films were formed on the zinc surface, resulting in that both the anodic and cathodic processes of zinc corrosion were inhibited remarkably; the corrosion protection efficiency values were increased; and the electrochemical impedance values were enhanced at least one order of magnitude. The low frequency impedance values for the composite coatings were increased at the initial stages of immersion in 5% sodium chloride solution, indicating the self-repairing activity of the composite coatings.     

Use of SVET and SECM to study the galvanic corrosion of an iron-zinc cell

The work makes use of the scanning vibrating electrode technique (SVET) and the scanning electrochemical microscope (SECM) to investigate microscopic aspects of the electrochemical reactions that occur in an iron-zinc galvanic couple immersed in aqueous sodium chloride solution. Detection of the corrosion processes was made by sensing the phenomena occurring in solution. The SVET provided information on the distribution of ionic currents arising from the metal surface, whereas the SECM measured the concentration of chemical species relevant to the corrosion processes. The two techniques had comparable sensitivity for the corrosion of iron but significant differences were observed concerning the detection of corrosion of zinc.     

Corrosion inhibition of copper in neutral chloride media by a novel derivative of 1,2,4-triazole

The efficiency of a new corrosion inhibitor, the bis-(4-amino-5-mercapto-1,2,4-triazol-3-yl)-butane (BAMTB), on copper was investigated in an aerated 3% NaCl solution using various techniques. Voltammetry, chronopotentiometry and electrochemical impedance spectroscopy (EIS) were performed to evaluate the inhibition efficiency of BAMTB. The surface layers were also characterized by Raman micro-spectroscopy and by scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDX). Potentiodynamic polarization curves showed that BAMTB is a mixed-type inhibitor for copper in neutral chloride solution and is even more efficient than the reference compound benzotriazole.     

Localized coating failure of epoxy-coated aluminium alloy 2024-T3 in 0.5 M NaCl solutions: Correlation between coating degradation, blister formation and local chemistry within blisters

The role of pH on the nature and rate of the degradation of epoxy coatings on AA2024-T3 panels and subsequent corrosion of the substrate during immersion in NaCl solutions was investigated. In acidic solutions both blister formation and growth are rapid. Blisters become very large (≈1 cm) and new blisters appear to form for a certain time after exposure. Often very small (∼0.1 mm) clear blisters surround these large blisters. Enhanced blister formation is due to irreversibly increased permeability of the coating for chloride ions and protons, the formation of more defect sites within the coating, and the weakening/dissolution of the oxide layer in low pH environments. In neutral pH solutions, coatings fail by forming one, or at most two, active blisters (red in color) within a few days of immersion with the time-to-failure dependent upon coating quality and thickness. Blister growth is a very slow process, and blister diameters rarely exceed a few millimeters even after several weeks. The accumulation of corrosion product within the blister slows down the corrosion rate and blister growth. The chloride concentration in the occluded solutions within the blister is significantly increased over the bulk concentration, and the pH is often in the acidic range. From electrochemical measurements it can be concluded that the anodic and cathodic reactions are confined to the blister and its immediate surroundings, rather than involving more of the surface over which the coating is intact. Based on corrosion morphology it is concluded that replated copper contributes to the overall cathodic reaction.     

Stable pit formation on AA2024-T3 in a NaCl environment

Scanning vibrating electrode (SVE), particle induced X-ray emission spectroscopy (PIXE) and standard electrochemical measurements were used to study the establishment of stable pits on AA2024-T3 in neutral sodium chloride solution (0.1 M NaCl). Pits were allowed to develop until hydrogen evolution was observed. Typical current at the mouth of the pits were in the vicinity of 1 mA. PIXE maps revealed the intermetallic (IM) particle distributions in the surface as well as significant chloride buildup around the pits. A significant fraction of the small selection of pits examined here appeared to have an S-phase particle (or remnant) within 20 μm of a AlCuFeMn type IM particle suggesting a coupling between the two. The electrochemistry of the coupling between different IM particle types was further investigated using potentiodynamic scans in 0.1 M aqueous NaCl solution of macroscopic electrodes made according to the IM particle compositions. Current densities at the open circuit potential of AA2024-T3 were largest, typically (0.2 up to 1 mA/cm²) for phases that were anodic with respect to AA2024-T3. Coupling of the IM particles was examined by comparing the degree of clustering around chloride attack sites to the average particle density for each map. There were significantly higher number of IM particles surrounding pit sites than the average IM particle densities indicating that local clustering played an important role in pit initiation.     

In situ monitoring the effects of a magnetic field on the open-circuit corrosion states of iron in acidic and neutral solutions

The effects of a 0.4 T horizontal magnetic field (HMF) on the open-circuit corrosion states of iron in static aqueous solutions are studied by in situ monitoring the responses of two electrochemical parameters to the applied magnetic field, i.e. the open-circuit potential (OCP) and the current under potentiostatic polarization. The applied magnetic field makes the OCP shift in the noble direction. Withdrawing the magnetic field causes a negative shift of the OCP in acidic solutions, but it does not cause any significant change of OCP in neutral solutions. Imposing a magnetic field induces a cathodic current for iron that was previously potentiostatically polarized at the OCP without magnetic field. Withdrawing the magnetic field induces an anodic current for iron that was previously potentiostatically polarized at the OCP with the magnetic field. The magnetic field effect is more significant in the acid solutions than in the salt solutions. The magnetic field effects on the oxygen reduction and on the activation-controlled iron dissolution reaction are found to be insignificant. The magnetic field effect on the hydrogen reduction reaction on iron in acidic solutions is demonstrated. Results show the possibility that a magnetic field would affect the hydrogen evolution by enhancing the electron-transfer process that has been categorized in the classical electrochemistry kinetics to be the rate-determining process. The memory effect of the magnetic field on the electrochemical reaction is identified and discussed.     

Corrosion behaviour of stainless steel fibre-reinforced copper metal matrix composite with reference to electrochemical response of its constituents

In this study, the corrosion behaviour of stainless steel fibre-reinforced copper metal matrix composite was investigated in chloride media at different temperatures and pH values using electrochemical techniques. The results were demonstrated in terms of the electrochemical response of the composite constituents. Microstructure observations of free corroded samples showed that the corrosion initiated at the copper matrix. Galvanic current density measurements demonstrated equilibrium polarity in which copper acted as the cell anode. The corrosion behaviour of the composite was predominantly determined by copper.     

Inhibitive action of the purine and adenine for copper corrosion in sulphate solutions

The influence of the concentration of the purine (PU) and adenine (AD) on the corrosion of copper in 0.5 M Na₂SO₄ solutions (pH 6.8) was studied. The investigations involved electrochemical polarization methods as well as electrochemical quartz crystal microbalance (EQCM) techniques. The inhibition efficiency increases with an increase in the concentration of PU and AD. Adherent layers of inhibitors were postulated to account for the protective effect. The adsorptions of inhibitors were found to occur on the surface of copper according to the Langmuir isotherm. The values of standard free energies of adsorption suggest the chemical adsorption of PU and AD on the copper surface.     

Films formed on copper surface in chloride media in the presence of azoles

The literature dealing with copper behaviour in chloride media in the presence of azoles is studied in order to improve understanding of their action mechanism, protective films formed, and the possibility of their application according to the inhibition efficiency achieved. The corrosion inhibition effect results from inhibitor molecule adsorption on copper surface and formation of the protective complex coating. According to the results summarised, copper corrosion may be successfully inhibited by benzotriazole, phenyl derivatives of tetrazole, bypyrazoles and 2-methyl-5-mercapto-1,3,4-thiadiazole in NaCl solutions, and in HCl solutions by 5-chloro benzotriazole, 3,5-diamino-1,2,4-triazole, and 4-methylimidazole.