The relation between adsorption bonding and corrosion inhibition of azole molecules on copper

Adsorption of plain azole molecules in protonated, neutral, and deprotonated forms on Cu(1 1 1) was characterized by density functional theory calculations. Both metal/vacuum and metal/water interfaces were considered and solvent effects were estimated by continuum solvation model. It is shown that chemisorptive bonding is by and large the strongest for deprotonated inhibitors. Only for imidazole the aqueous-phase adsorption free energy of the neutral form is comparable to that of deprotonated form. This suggests that for imidazole—because of its more basic nature—the neutral form and for triazole and tetrazole their deprotonated forms are the active species for inhibiting corrosion.     

Inhibition of copper corrosion by 1,2,3-benzotriazole: A review

Benzotriazole (BTAH) has been known for more than sixty years to be a very effective inhibitor of corrosion for copper and its alloys. In spite of numerous studies devoted to the investigation of BTAH action, the mechanism of its action is still not completely understood. The aim of this review is to summarize important work in the field of BTAH as a copper corrosion inhibitor, from the early discoveries to the present time. Special attention is given to the BTAH surface structure. The disagreement between findings and mechanisms is discussed.     

Polyacrylic acid as a corrosion inhibitor for aluminium in weakly alkaline solutions. Part I: Weight loss, polarization, impedance EFM and EDX studies

This part is devoted to study the influence of three selected polyacrylic acids (PAAs) with different molecular weights (PAA1 = 1800, PAA2 = 11,000 and PAA3 = 14,000 g mol⁻¹) on the corrosion inhibition of Al in weakly alkaline solutions (pH 8 and 10) at 30 °C. Measurements were conducted under different experimental conditions using chemical (weight loss) and electrochemical (potentiodynamic polarization and impedance) techniques, complemented with ex situ energy dispersive X-ray (EDX) examinations of the electrode surface. Electrochemical frequency modulation (EFM), a non-destructive corrosion measurement technique that can directly give values of corrosion current without prior knowledge of Tafel constants, is also presented here. The results demonstrated that these polymers inhibit the alkaline corrosion of Al. The inhibition effect of these polymers is due to their adsorption on Al surface. The isoelectric point (IEP) of aluminium oxide (pH 9) seems to be an important factor controlling corrosion inhibition and adsorption of the three polymers. The three polymers inhibit the corrosion reaction of aluminium excellently at pH 8, but less effectively at pH 10. Polarization measurements showed that the three polymers act as mixed-type inhibitors. The inhibition efficiencies of these polymers increase with increasing concentration, molecular weight and immersion time. Results obtained from the chemical and electrochemical measurements are in good agreements.     

Applications of chemometric tools in corrosion studies

The aim of this review is to introduce the reader to the applications of chemometric techniques in the field of corrosion science, which currently are not commonly spread. By means of key examples it will be shown how they can be fruitfully applied and enhance the quality of a laboratory workflow.     

Behaviour of copper during alkaline corrosion of Al–Cu alloys

Enrichment of copper beneath amorphous anodic films on relatively dilute, solid-solution Al–Cu alloys is necessary before copper can be oxidized and incorporated into the oxide layer. A similar enrichment arises during electropolishing, which also develops an amorphous oxide. In these cases, external polarization is applied, usually generating a relatively high oxidation rate. In contrast, enrichment behaviour at the corrosion potential has received less attention. The present study examines the corrosion of Al–Cu alloys, containing up to 6.7 at.% Cu, in 0.1 M sodium hydroxide solution at 293 K. Copper is again found to enrich in the alloy, similarly to behaviour with anodic polarization. However, following enrichment, discrete copper-rich particles appear to be generated in the corrosion product. These are suggested to be nanoparticles of copper, since the corrosion potentials of the alloys are low relative to that required for oxidation of copper. The corrosion rate increases with increase of both time and copper content of the alloy, probably associated with a greater cathodic activity due to an increasing number of nanoparticles. The corrosion proceeds with loss of aluminium species to the sodium hydroxide solution, but with retention of copper in the layer of hydrated alumina corrosion product.     

Electrochemical corrosion testing of fasteners in extracts of treated wood

A recent change in wood preservatives has highlighted the need for a rapid, quantitative test to measure the corrosion rates of metals in contact with treated wood that could be used to evaluate new fasteners or new wood preservatives. A new method was developed where polarisation resistance tests were conducted on fasteners exposed to a water extract of wood treated with alkaline copper quaternary (ACQ). Good correlation was found between the corrosion rates using this new method and previous one year exposure data for carbon steel, hot-dip galvanized and electroplated galvanized fasteners. These data suggest that polarisation tests run in wood extract may be an effective, rapid test method to evaluate new fasteners or wood preservatives.     

Novel thiophene symmetrical Schiff base compounds as corrosion inhibitor for mild steel in acidic media

The inhibiting effect of two Schiff bases on the corrosion of the mild steel (MS) in 1 M HCl has been studied by electrochemical impedance spectroscopy (EIS) and Tafel polarisation measurements. The Schiff bases, 4,4′-bis(3-carboxaldehyde thiophene) diphenyl diimino ether (L₁) and 4,4′-bis(3-carboxaldehyde thiophene) diphenyl diimino ethane (L₂), were synthesized using 3-carboxaldehydethiophene and its corresponding amine. Polarisation curves reveal that both compounds are mixed type (cathodic/anodic) inhibitors and inhibition efficiency (% IE) increases with increasing concentration of compounds. It is suggested that their effects depend on their concentrations and the molecular structures. Adsorption of compounds on mild steel surface is spontaneous and obeys Langmuir’s isotherm.     

Inhibitive properties of quaternary ammonium bromides of N-containing heterocycles on acid mild steel corrosion. Part II: EIS results

Four quaternary ammonium bromides of different heterocyclic compounds were investigated as corrosion inhibitors of mild steel in 1 N HCl using electrochemical impedance spectroscopy. The results were compared with data obtained by the polarisation resistance method. The influence of concentration and temperature (30-60 °C) was checked as well. Two structure models were found to describe the processes taking place at the interface mild steel/1 M HCl + inhibitor. The simpler one can be considered as a degeneration of the more complex one when the two time constants approach similar values. By fitting the structural models to the experimental results the parameter values were evaluated, as well as the time constants. A good correlation was established between the EIS and the polarisation resistance results.     

Field studies of corrosion behaviour of copper alloys in natural seawater

Eight copper alloys were tested in a one-year field deployment in the North Atlantic Ocean. The corrosion behaviour was characterized by weight loss, optical and electronic microscopy analyses. The biofouling performance was quantified in terms of the biomass accumulation. The testing program included specimens in tensioned and untensioned configurations, as well as a set for seasonal deployments. The seasonal corrosion rates were 140% higher, and the rates of tensioned specimens were 39% higher than those of the untensioned specimens after 12 months of deployment. Good biofouling resistance was observed for all but one alloy, which exhibited heavy fouling by barnacles.     

Inhibitive properties of quaternary ammonium bromides of N-containing heterocycles on acid mild steel corrosion. Part I: Gravimetric and voltammetric results

Four quaternary ammonium bromides of different heterocyclic compounds were investigated as corrosion inhibitors of mild steel in 1 M HCl and 1 M H₂SO₄. Polarisation curves, polarisation resistance and gravimetric methods were used. The inhibitor efficiency was found to depend on both concentration and temperature. The inhibitors were of mixed type, influencing predominantly the anodic process. From the temperature dependences the apparent activation energy in 1 M HCl was determined in the presence of all studied compounds, found to be inferior to the activation energy in absence of inhibitor. The adsorption of the inhibitors was well described by the Frumkin or the Langmuir adsorption isotherms in both acidic media and the adsorption isotherm parameters were determined at room temperature. The influence of the molecular structure was discussed taking into account the different number of positive charges and the different heterocycles. The best inhibitive properties had 1-(carbamoylethyl)-4-methylpyridinium bromide.     

Corrosion characteristics of copper microparticles and copper nanoparticles in distilled water

The corrosion characteristics of copper microparticles and copper nanoparticles in distilled water were investigated in this paper. The Cu²⁺ transformations of copper microparticles and copper nanoparticles in distilled water were tested by using absorbance measurement, the structures of their corrosion products were determined by using XRD and TEM techniques. The results of absorbance measurement show that the corrosion characteristics of copper nanoparticles in distilled water are quite different from that of copper microparticles. The Cu²⁺ transformations ratio of copper microparticles increases slowly with the increasing of immersion time and levels off eventually, but the Cu²⁺ transformations ratio of copper nanoparticles increases sharply with the increasing of immersion time and gets to peak rapidly, and then decreases as the immersion time increases and levels off finally. The results of XRD present that they have different corrosion products, the corrosion products of copper microparticles in distilled water are Cu and CuO, but the nanoparticles are Cu, CuO, Cu(OH,Cl)₂ · 2H₂O and Cu₂(CO₃)(OH)₂. All these differences owe to the size effect of copper particles.     

Enhanced corrosion resistance of carbon steel in normal sulfuric acid medium by some macrocyclic polyether compounds containing a 1,3,4-thiadiazole moiety: AC impedance and computational studies

We report here the use of macrocyclic polyether compounds containing a 1,3,4-thiadiazole moiety (n-MCTH) in the corrosion inhibition of C38 carbon steel in 0.5 M H₂SO₄ acid medium.

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The aim of this work is devoted to study the inhibition characteristics of these compounds for acid corrosion of C38 steel using electrochemical impedance spectroscopy (EIS). Data obtained from EIS show a frequency distribution and therefore a modeling element with frequency dispersion behaviour, a constant phase element (CPE) has been used. The experimental results obtained revealed that these compounds inhibited the steel corrosion in acid solution and the protection efficiency increased with increasing inhibitors concentration. The difference in their inhibitive action can be explained on the basis of the number of oxygen atoms present in the polyether ring which contribute to the chemisorption strength through the donor acceptor bond between the non bonding electron pair and the vacant orbital of metal surface. Adsorption of n-MCTH was found to follow the Langmuir’s adsorption isotherm. The thermodynamic functions of adsorption process were calculated and the interpretation of the results is given. These results are complemented with quantum chemical study in order to provide an explanation of the differences between the probed inhibitors. Correlation between the inhibition efficiency and the structure of these compounds are presented.     

The role of chelating agents on the corrosion mechanisms of aluminium in alkaline aqueous solutions

The influence of 1,2-diaminoethane (DAE) on the mechanism of aluminium corrosion in KOH solutions at pH 13 was investigated by combining time-resolved inductively coupled plasma optical emission spectrocopy, open-circuit potential measurements and X-ray photoelectron spectroscopy. In pure KOH solutions, a very slow corrosion rate is initially observed, corresponding to the dissolution of the native oxide layer. Following this incubation stage, the corrosion rate is increasing due to the formation and oxidation of Al hydride, until a steady state is reached. DAE behaves as a strong initial corrosion accelerator, due to synergistic effects with hydroxyl ions and a dissolution mechanism in three successive steps has been proposed: (i) a rapid initial dissolution induced by the formation and detachment from the surface of bidentate (chelate) Al-DAE metal bound surface complexes; (ii) a slower step ascribed to the formation and release of monodentate Al-DAE metal bound surface complexes and (iii) a final step dominated by direct oxidation of surface aluminium hydride by hydroxyl species as in pure KOH.     

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.     

Classification of corrosion defects in NiAl bronze through image analysis

Corrosion surface damage in the form of pitting and micro-cracks is observed in many metals. Cracks usually initiate from the pits and grow under cyclic stresses and eventually lead to material failure. An image analysis based on wavelet transforms and fractals was used to study the corrosion morphology of nickel aluminum bronze metal under varying corrosion conditions and applied stresses. Image feature parameters were extracted and analyzed to classify the pits/cracks in the metal samples. The results obtained indicate that classification of pits/cracks is possible with image analysis and may be used for correlating service/failure conditions based on corrosion morphology.     

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.     

Hydrogen embrittlement risk of high strength galvanized steel in contact with alkaline media

The critical conditions for hydrogen embrittlement (HE) risk of high strength galvanized steel (HSGS) wires and tendons exposed to alkaline concrete pore solutions have been evaluated by means of electrochemical and mechanical testing.There is a relationship between the hydrogen embrittlement risk in HSGS and the length of hydrogen evolution process in alkaline media. The galvanized steel suffers anodic dissolution simultaneously to the hydrogen evolution which does not stop until the passivation process is completed. HSGS wires exposed to a very high alkaline media have showed HE risk with loss in mechanical properties only if long periods with hydrogen evolution process take place with a simultaneous intensive galvanized coating reduction.     

Corrosion and corrosion test methods of zinc coated steel sheets on automobiles

The effect of zinc and zinc alloy coated steel sheets on perforation corrosion in actual automobiles and the relevant accelerated corrosion test methods were studied. The main factor affecting corrosion in the crevice of lapped panels was the coating weights of zinc and zinc alloys rather than the type of coating. Perforation corrosion process of galvanized steel in the crevice of lapped portion in automobiles was divided in four stages. Based on the analysis of corrosion in actual automobiles, a Perforation Corrosion Index, PCI for lapped steel panels was proposed. Assuming PCI for various accelerated corrosion test methods, the corrosion resistance of various types of coated steel sheets in actual environments was evaluated.     

Effect of common water contaminants on the corrosion of aluminium alloys in ethylene glycol-water solution

The effects of common water contaminants of chloride (Cl⁻), cupric (Cu²⁺) and ferric (Fe³⁺) ions, in four different mixture combination of Fe³⁺ + Cu²⁺, Cl⁻ + Fe³⁺, Cl⁻ + Cu²⁺ and Cl⁻ + Fe³⁺ + Cu²⁺, were examined on the corrosion behaviour of aluminium alloys in ethylene glycol-water solution, using mass loss technique. The highest material losses were recorded for the two alloys in ethylene glycol solution containing the combination of the chloride and the two heavy metal ions. The corrosivity of the solution in the presence of the combination of ions was in the order of Cl⁻ + Fe³⁺ + Cu²⁺ > Cl⁻ + Cu²⁺ > Cl⁻ + Fe³⁺ > Fe³⁺ + Cu²⁺. The results gave first-order kinetics with respect to aluminium in ethylene glycol solution-ion systems. Alloy 3SR exhibits maximum corrosion in all the solutions. It is concluded that the two commercial alloys in the solution polluted with all the three ions would not be able to survive for reasonable period of time without corrosion inhibitor.     

Understanding corrosion via corrosion product characterization: I. Case study of the role of Mg alloying in Zn-Mg coating on steel

In the present work the corrosion inhibitive role of Mg in Zn-Mg coatings is considered for different stages of corrosion. Corrosion product characterization was carried out using XRD, IRRAS, MEB-FEG-EDS on technical Zn-Mg coatings after various exposure times in a standardized cyclic corrosion test. The results are compared with artificial corrosion products obtained by chemical and electrochemical synthesis. The importance of the ageing and the role of the atmospheric CO₂ on the nature and morphology of the corrosion products are discussed. The corrosion resistance of Zn-Mg alloy is correlated with the stabilization of simonkolleite against its transformation into smithsonite, hydrozincite, and zincite during ageing cycles in presence of CO₂. The stabilization appears to be due to the preferential formation of magnesium carbonates. Thermodynamic modeling and titrometric analysis demonstrate that Mg²⁺ enhances simonkolleite during dry-wet cycling by (1) removing carbonate from the environment and thereby limiting of the transformation of simonkolleite into zincite, smithsonite, and hydrozincite and by (2) buffering the pH of the electrolyte around 10.2 due to the precipitation of Mg(OH)₂ preventing the dissolution of zinc based corrosion products into soluble hydroxide complexes.