2-Mercaptobenzoxazole as a copper corrosion inhibitor in chloride solution: Electrochemistry, 3D-profilometry,and XPS surface analysis

2-Mercaptobenzoxazole (MBOH) was studied as a corrosion inhibitor for Cu in 3 wt.% NaCl solution using EIS, a potentiodynamic curve, 3D-profilometry, and XPS measurements. It was shown that Cu corrosion in solution containing MBOH follows kinetic-controlled and diffusion-controlled processes and that MBOH is a mixed-type inhibitor. The diffusion coefficient of the Cu ions travelling through the solid surface layers was estimated to be on the order of 10⁻¹⁵–10⁻¹⁴ cm² s⁻¹. It was also demonstrated that the Cu(I)–MBOH complex is formed on the Cu surface and that the thickness of this surface layer is 1.4 ± 0.4 nm.     

Some aspects of copper corrosion in presence of benzotriazole and chloride ions

This paper deals with the investigation of electrochemical behaviour of copper in a sodium tetraborate (borax) solution in the presence and absence of chloride ions. The influence of benzotriazole (BTA) on the anodic behaviour of copper was also investigated. It was found that Cu₂O and CuO oxides were formed on copper and that peak current moved to the positive side with increased immersion time in a sodium tetraborate solution. After 1 h immersion of the copper electrode in a sodium tetraborate solution containing various chloride ion concentrations (0.001, 0.010, 0.050, and 0.100 mol/dm³ Cl⁻) the activation effect of those ions was found, whereas after 6 h immersion of copper in the above mentioned solutions, chloride ions were found to have not only activation but also passivation effect. The investigation of the effect of benzotriazole led to a conclusion that BTA has an inhibiting effect with increasing immersion times (15 min, 1 h, 4 h, and 48 h) as well as with increasing BTA concentrations (8.4 × 10⁻⁶, 8.4 × 10⁻⁵, 8.4 × 10⁻⁴, and 8.4 × 10⁻³ mol/dm³). In addition, at the lowest investigated BTA concentration (8.4 × 10⁻⁷ mol/dm³) an activation effect of this compound on copper dissolution was observed. Based on the Langmuir adsorption isotherm, the value of the standard free energy adsorption was found to be ΔG⁰ = −35.4 kJ/mol.     

Computer simulation of the corrosion inhibition of copper in acidic solution by alkyl esters of 5-carboxybenzotriazole

A series of alkyl esters (methyl, butyl, hexyl, and octyl) synthesised from a mixture of 4- and 5-carboxybenzotriazole (4-CBTAH and 5-CBTAH) inhibited copper corrosion in aerated solution (pH∼0). Inhibition efficiency (IE%) of the protonated esters (CBTAH₂⁺-R) increased with hydrocarbon chain length and this is attributed to chemisorption (through azole ring N) and increased physical adsorption as more methyl groups are introduced. A modelling package employing molecular mechanics and molecular dynamics has been used to simulate the docking of a single protonated species (5-CBTAH₂⁺-R) onto a clean copper (1 1 0) surface. A decrease in potential energy was associated with the flattening of the ester ring system onto the surface and further decreases in energy were associated with the extension of the aliphatic chain onto the surface. The crude binding energy (E_bind) of each ester with the surface was estimated and this energy also increased regularly with carbon chain length. The study suggests that molecular modelling and calculation of E_bind of a single molecule on a specified metallic surface can be used to predict the inhibition performance of compounds whose structures change in a regular way.     

New insights into copper corrosion in presence of benzotriazole and chloride ions

The effect of Cl^– concentration and temperature on the copper corrosion in NaCl solution in presence of 40?mg?L^–1 benzotriazole was investigated using cyclic voltammetry, electrochemical impedance spectroscopy, electrochemical noise (EN) and scanning electron microscopy (SEM). Results revealed that the charge transfer resistance decreased with increasing the Cl^– concentration and temperature. The EN generated at low Cl^– concentration and low temperature had small noise amplitude, while the EN showed large potential oscillation amplitude in the case of high Cl^– concentration and high temperature. A parameter, named corrosion active energy C_AE, was proposed to further study the relationship between the EN feature and corrosion rate and corrosion severity (SEM). The variation trend of corrosion active energy C_AE with Cl^– concentration and temperature was found to be opposite with energy gap E_g and charge transfer resistance. Thus, C_AE shows a promising potential to in situ evaluate the corrosion rate and corrosion severity.     

XPS studies on passive film formed on stainless steel in a high-temperature and high-pressure methanol solution containing chloride ions

The composition and structure of passive film formed on 316L SS immersed in an anhydrous methanol solution (water content < 0.05 wt%) containing 0.42 wt% LiCl at 323-473 K were investigated by X-ray photoelectron spectroscopy (XPS), and compared with those of film formed in an aqueous solution. The passive film formed in the methanol solution was mainly composed of Fe and Cr oxides, and it possessed a double-layered structure consisting of an Fe oxide-rich outer layer and a Cr oxide-rich inner layer. Dissolution of the Fe-rich layer and densification of the Cr-rich inner layer were observed, especially at high temperatures. However, these were suppressed in an aerated methanol solution at 423 K or below, probably due to the barrier effect of adsorbed oxygen. No Ni compound contributed to composing the passive film, even at higher temperatures. The ratio of OH⁻ to O²⁻ was small and decreased with an increase in temperature (the presence of oxygen suppressed the decrease, especially at 423 K or below). The chloride ions were concentrated in the Fe-rich outer layer, and they penetrated more deeply than that in the aqueous solution into the passive film formed in the methanol solution.     

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.     

Electrochemical impedance spectroscopy study of surface films formed on copper in aqueous environments

The electrochemical behavior of pure copper has been studied in aqueous environments using linear polarization and electrochemical impedance spectroscopy (EIS) techniques as a function of immersion time. The effect of pollutants (like chloride, sulfide and ammonium ions) on the nature of films formed on the copper surface has been studied. All the surfaces revealed the presence of a porous oxide layer. The corrosion resistance decreased with increasing amount of chloride ions. The addition of Na₂S in the environments in the absence of any chloride species was beneficial for corrosion resistance. EIS data suggested that the capacitance of the films formed in chloride environments was higher. The surfaces obtained in presence of chloride ions were relatively rough and deeply attacked. The total impedance decreased after 432 h of immersion in solutions possessing chloride ions. The damaging role of chloride ions and the relatively less severe effect of sulfide ions were noted.     

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.     

Effects of benzotriazole on anodized film formed on AZ31B magnesium alloy in environmental-friendly electrolyte

An environmental-friendly electrolyte of silicate and borate, which contained an addition agent of 1H-benzotriazole (BTA) with low toxicity (LD50 of 965 mg/kg), was used to prepare an anodized film on AZ31B magnesium alloy under the constant current density of 1.5 A/dm² at room temperature. Effects of BTA on the properties of the anodized film were studied by scanning electron microscopy (SEM), energy dispersion spectrometry (EDS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), loss weight measurement, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS), respectively. The results demonstrated that anodized growth process, surface morphology, thickness, phase structure and corrosion resistance of the anodized film were strongly dependant on the BTA concentration, which might be attributed to the formation of an BTA adsorption layer on magnesium substrate surface. When the BTA concentration was 5 g/L in the electrolyte, a compact and thick anodized film could provide excellent corrosion resistance for AZ31B magnesium alloy.     

Comparison of rolled and heat treated SS304 in chloride solution using electrochemical and XPS techniques

SS304 in the rolled condition (66% cold work) and in the heat treated condition (solution quenched from 1100 °C) was assessed for its electrochemical behavior in de-aerated 3.5% NaCl by potentiodynamic polarization and AC impedance techniques. Surface analysis of films formed on the two materials in air and in solution was done using XPS. Open circuit potential (OCP) and pitting potential of the rolled SS304 were seen to be −0.25 V vs standard calomel electrode (SCE) and 0.25 V vs SCE respectively, while the heat treated sample showed −0.33 V vs SCE and 0.06 V vs SCE respectively. The rolled material showed a passive current density of 0.9 μA cm⁻², which was about one order lower than that shown by the heat treated material. The rolled material, in addition, exhibited repassivation at 0.085 V vs SCE during reverse scanning of potential. Repassivation was not observed in the heat tread sample. XPS showed that films on rolled material were richer in chromium as compared with those on heat treated alloy. Better passivation characteristics shown by the rolled material were attributed to thicker passive film with a higher Cr:Fe ratio, the higher Cr being the result of enhanced diffusion through the oriented grains in the rolled material.     

Impedance studies of the inhibitive effect of benzotriazole on the corrosion of copper in sodium chloride medium

Impedance studies of a copper electrode in chloride medium with or without benzotriazole (BTA) were made over a wide frequency range (10^?2?10²KHz). The impedance characteristics of the Cu-BTA surface film were established under various experimental conditions. The results indicate that the film was of a dielectric nature having a dielectric constant of ca. 20. It was found that the film thickness increased and the corrosion rate decreased by increasing the BTA-concentration or with ageing. It was assumed that, at the stationary state, the rate of dissolution of Cu-BTA film blanced that of the slow transport of Cu ions through the film. Good support for these results was obtained from the data of potentiostatic polarization and weight loss measurements.     

Photoacoustic study on cathodic reduction of anodic oxide films formed on copper in borate solution

An in-situ photoacoustic (PAS) technique, using a piezoelectric detector with high sensitivity was applied to the study on duplex oxide films anodically formed on copper in pH 8.4 borate solution. The PAS signals from the copper electrode were produced by an irradiation of light beam with a wavelength of 514.5 nm. The PAS amplitude during cathodic reduction of the outer oxide layer to Cu₂O changed in the opposite direction, depending on the anodic potential of film formation and oxidation time. Assuming that the change in PAS amplitude is proportional to both optical absorption coefficient and film thickness, it was deduced from comparison of the estimated absorption coefficients for Cu (OH)₂, CuO and CuO_0.67 films that dehydration of the outer layer having an average composition of CuO_x (OH)_2?2x proceeded with increasing anodic potential of film formation and oxidation time during growth of the duplex oxide film. Moreover, it was found that the change in PAS amplitude during cathodic reduction of the total Cu₂O film involving the inner layer to metallic copper was proportional to the electric charge required for cathodic reduction, i.e., the film thickness, irrespective of anodic potential of film formation and oxidation time, which proved the validity of the above assumption.     

Corrosion inhibition of copper by potassium ethyl xanthate in acidic chloride solutions

The influence of pH and concentration of potassium ethyl xanthate (KEtX) on the spontaneous dissolution of copper in acidic chloride solutions containing oxygen has been studied. The degree of copper protection increases with an increase in pH and concentration of KEtX. An adherent layer of inhibitor is postulated to account for the protective effect. The adsorption of KEtX has been found to occur on the surface of copper according to the Langmuir isotherm. KEtX is chemically adsorbed on the copper surface.     

Multianalytical in-situ investigations of the early stages of corrosion of copper, zinc and binary copper/zinc alloys

A new experimental infrared reflection absorption spectroscopy (IRRAS) set-up for in-situ investigation of corrosion phenomena occurring in the metal–atmosphere interface was developed. It was applied in combination with in-situ tapping-mode atomic force microscopy (TM-AFM) and phase detection imaging (PDI) to study the early stages of corrosion of pure copper and pure zinc as well as to determine the influence of increasing zinc contents in brass. Additionally, ex-situ secondary ion mass spectrometry (SIMS) investigations were carried out on the samples after exposure.The investigations were accomplished in synthetic air with 80% relative humidity (RH) and synthetic air with 80% RH and 250 ppb SO₂. The experiments showed that an increase of the zinc content in the brass alloy yields to an increase of the dimension of the corrosion features formed on the metal surface during weathering. Large features on top of smaller features were observed with TM-AFM on the surfaces exposed to SO₂-containing humidified air, which could be identified by IRRAS as metal sulphur compounds. Furthermore, an increased amount of physisorbed water on the metal surfaces was determined with IRRAS in dependence of the increasing zinc content in the brass samples.     

Electrochemical and XPS studies of the passive film formed on stainless steels in borate buffer and chloride solutions

The passivity of AISI 304L and AISI 316L stainless steels in a borate buffer solution, with and without the addition of chloride ions, was studied using cyclic voltammetry and potentiodynamic measurements. The passive layers formed by electrochemical oxidation at different passivation potentials on both the stainless steels were studied by X-ray photoelectron spectroscopy, their compositions were analysed as a function of depth, and the cationic fraction of the passive film was determined. The passive films established on the two stainless steels in the borate buffer solution at pH = 9.3 contained the oxides of two main elements, i.e., Fe and Cr. The oxides of the alloying elements Ni and, optionally, Mo, also contribute to the passive layer. In the presence of chloride ions a strong chromium enrichment was observed in the passive layers.     

Fast etching of copper in thionyl chloride/acetonitrile solutions

We report fast etching of copper (Cu) in thionyl chloride (SOCl₂)/acetonitrile (CH₃CN) solutions. The etching rate can be tuned over a wide range by varying the concentration of the etchant, and the stirring rate of the liquid. The etching rate reaches 36 mg min⁻¹ cm⁻² in 1 mol L⁻¹ SOCl₂/CH₃CN under stirring at room temperature, which is much faster than any currently used etchant for Cu. With sonication, the etching rate reaches 320 mg min⁻¹ cm⁻². The chemical reactions involved are studied by X-ray photoelectron spectroscopy and Raman spectroscopy. The fast etching may find important applications in microelectronics.     

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.     

Stress corrosion cracking of copper and silver, specific effect of the metal cations

Based on stress corrosion cracking (SCC) studies on brass, and on Ag-Cd alloys (a model alloy used to reproduce the behaviour of brass), it was found that both pure copper and pure silver are susceptible to SCC in 1 M copper(II) nitrate and in 1 M silver nitrate aqueous solutions, at the equilibrium potentials for the reactions: Cu²⁺+2e⁻↔Cu and Ag⁺+e⁻↔Ag, respectively. The results were analysed under the light of recent developments in surface science. It was concluded that the same SCC mechanism that operates in brass and in Ag-Cd alloys should be operating during SCC of pure copper and pure silver, under equivalent experimental conditions.     

A study on new benzotriazole derivatives as inhibitors on copper corrosion in ground water

The corrosion inhibition properties of newly synthesized 1-(2-pyrrole carbonyl)-benzotriazole (PCBT) and 1-(2-thienyl carbonyl)-benzotriazole (TCBT) in combination with the non-ionic surfactant Triton X-100 (TX-100) on metallic copper were studied in ground water environment and the results were compared with benzotriazole (BTA). Various electrochemical studies such as open circuit potential (OCP), potentiodynamic polarization, ac impedance and cyclic voltammetric (CV) were made. Surface analytical techniques like FT-IR and XRD were also performed. The results indicated that PCBT is a better corrosion inhibitor for copper and the formulation consisting of PCBT and TX-100 offered improved inhibition efficiency (IE) in a synergistic manner.     

Copper corrosion mitigation by binary inhibitor compositions of potassium sorbate and benzotriazole

This work presents the combined effect of two inhibitors, potassium sorbate (2,4-hexadienoic acid potassium salt) and 1,2,3-benzotriazole, on the corrosion behavior of copper in sulfate based solutions. Individual and combined characteristics of copper corrosion inhibition in sulfate solution in the presence of potassium sorbate (K-sorbate) and benzotriazole (BTAH) were studied with the use of electrochemical, microscopic and spectroscopic methods. Whereas, BTAH alone protects copper from corrosion attack in sulfate solutions only in a limited potential range below 0.4 V vs. saturated calomel electrode (SCE), the presence of K-sorbate combined with BTAH in such solutions enables the protection of the copper surface at potentials above 0.4 V_SCE. The mixture of both inhibitors provides supplementary and robust corrosion protection of Cu over a wide potential range.