Studies on alkyl esters of carboxybenzotriazole as inhibitors for copper corrosion

A series of alkyl esters (methyl, butyl, hexyl, octyl) derived from carboxybenzotriazole (CBTAH) have been studied as inhibitors for copper. Coupon tests established that the inhibition efficiency (IE) is concentration, time and pH dependent. At pH∼0 the IEs of the octyl and hexyl esters are considerably higher than that for benzotriazole under similar conditions. As pH increases up to approximately 8 the IE of each ester is decreased, but is still sufficient for practical use. For the butyl and methyl esters an opposite trend was observed; IE increased with increased pH. In acidic sulphate solution (pH∼0) the IE was in the order: octyl>hexyl>butyl>methyl, whilst in the near-neutral solution (pH∼8) this order is reversed. It is proposed that the protonated species (CBTAH₂⁺-R) is chemisorbed on the copper through an azole nitrogen and at low pH IE is determined by van der Waals' forces of attraction between adjacent alkyl chains oriented away from the copper surface, which are increased with the length of the alkyl chain. On the contrary it is proposed that at high pH a polymeric complex is formed and steric hindrance acts to make the film less protective. Polarisation, EIS and SERS studies confirm these hypotheses.     

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.     

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 characterisation of the protective film formed by benzotriazole on the 90/10 copper-nickel alloy surface in H2SO4 media

The nature of the protective film formed by benzotriazole (BTAH) on the surface of the 90/10 CuNi alloy in deaerated 0.5 mol L⁻¹ H₂SO₄ solution containing Fe(III) ions as oxidant was investigated by weight-loss, calorimetric measurements, and by surface-enhanced Raman spectroscopy (SERS). The SERS measurements show that the protective film is composed by the [Cu(I)BTA]_n polymeric complex and that the BTAH molecules are also adsorbed on the electrode surface. A modification of the BET isotherm for adsorption of gases in solids is proposed to describe the experimental results obtained from weight-loss experiments that suggest an adsorption in multilayers. Electrochemical studies of copper and nickel in 0.5 mol L⁻¹ H₂SO₄ in presence and absence of BTAH have also been made as an aid to interpret the results. The calculated adsorption free energy of the cuprous benzotriazolate on the surface of the alloy is in accordance with the value for pure copper.     

Electrochemical corrosion behaviour of microcrystalline aluminium in acidic solutions

The electrochemical corrosion behaviour of microcrystalline pure aluminium coating, fabricated by a magnetron sputtering technique, has been investigated in both 0.5 mol/l NaCl and 0.5 mol/l Na₂SO₄ acidic (pH = 2) aqueous solutions. The corrosion resistance of the microcrystalline Al coating has deteriorated more compared with that of the cast pure Al in Na₂SO₄ acidic solution. However, its oxide film has a higher pitting resistance in the NaCl acidic solution. Chloride ions play a big role in the formation of the oxide film on the microcrystalline Al coating. The higher pitting resistance was attributed to the more acidic isoelectric point which the oxide film achieved.     

Radiotracer study of embedding of SO4 and Cl ions into the surface film formed on Mn corroding in perchlorate solution

The adsorption of radiolabelled Cl⁻ and SO₄⁻ ions from aqueous perchlorate solutions onto powdered Mn metal was studied. It was found that the extent of the adsorption is determined by the continuous increase of the thickness of the surface oxide/hydroxide layer formed as a consequence of the slow corrosion of the metal in neutral or quasi-neutral media. At low pH values (pH < 6) the extent of the adsorption decrease significantly owing to the dissolution of the surface layer. At high pH values (pH > 10) the adsorption decreases presumably owing to the competitive adsorption of OH⁻ ions or the modification of the adsorption centres by some kind of deprotonation.     

Semiconductor properties and protective role of passive films of iron base alloys

Semiconductor properties of passive films formed on the Fe-18Cr alloy in a borate buffer solution (pH = 8.4) and 0.1 M H₂SO₄ solution were examined using a photoelectrochemical spectroscopy and an electrochemical impedance spectroscopy. Photo current reveals two photo action spectra that derived from outer hydroxide and inner oxide layers. A typical n-type semiconductor behaviour is observed by both photo current and impedance for the passive films formed in the borate buffer solution. On the other hand, a negative photo current generated, the absolute value of which decreased as applied potential increased in the sulfuric acid solution. This indicates that the passive film behaves as a p-type semiconductor. However, Mott-Schottky plot revealed the typical n-type semiconductor property. It is concluded that the passive film on the Fe-18Cr alloy formed in the borate buffer solution is composed of both n-type outer hydroxide and inner oxide layers. On the other hand, the passive film of the Fe-18Cr alloy in the sulphuric acid consists of p-type oxide and n-type hydroxide layers. The behaviour of passive film growth and corrosion was discussed in terms of the electronic structure in the passive film.     

Corrosion and adhesion study of polyurethane coating on silane pretreated aluminum

In this paper, the effect of silane pretreatment pH on adhesion strength and corrosion protection of subsequent polyurethane (PU) coating on aluminum alloy substrate is evaluated. Practical adhesion of the coating on substrate was measured in dry, wet and recovered states via pull-off method for desmutted, chromated and vinyltrimethoxysilane (VTMS) pretreated aluminum alloy (AA1050). VTMS resulted in good adhesion performance in dry, wet and recovery states for VTMS treated specimens at pH < isoelectric point (IEP) which is related to the silanol groups orientation toward aluminum surface. Adhesion performance at pH > IEP is lower than desmutted specimens which can be related to presence of unreacted VTMS molecules on the surface. Vinyl groups orientate toward the aluminum surface at pH above IEP, results in prevention of VTMS reaction on the surface. Corrosion protection of PU coating was studied with electrochemical impedance spectroscopy (EIS) and salt spray in the presence of silane layer; then, compared to coated desmutted and chromated specimens. Water sensitivity of unreacted VTMS molecules leads to poor protective performance of specimens treated at pH > IEP. However, at pH < IEP protective performance is considerably higher than desmutted and comparable with chromated specimens.     

The effect of 180 °C-annealing on the electrochemical behavior of nano-thick zinc-electroplated copper in aqueous solutions with different pH

The anodic polarization and a.c. impedance measurements of 4 nm- and 25 nm-zinc-electroplated copper specimens were conducted in aqueous solutions with four different pH-values. The nano-thick zinc-electroplated copper was tested after electroplating and annealing at 180 °C for 1, 2 and 3 h, respectively. The results showed that the open-circuit potential (OCP) of 25 nm-zinc electroplated copper shifted toward noble potential after annealing. A more noble OCP of 25 nm zinc-electroplated copper could be achieved when zinc plated copper was annealed at 180 °C up to 1 h. Similar change was found for 4 nm-zinc electroplated copper only in neutral and alkaline solutions. The a.c. impedance response of all nano-thick zinc-electroplated copper corresponded to two Randle’s circuits in series, in which the circuit measured in a high frequency region of their Nyquist diagrams revealed the electrochemical behavior of nano-thick zinc deposits. The charge transfer resistance of the nano-thick zinc electroplated copper was significantly raised after annealing at 180 °C when tested in pH 9.5 solution. Microstructures of the aforementioned nano-thick zinc electroplated copper were examined with cross-sectional TEM specimens. A distinct phase interface between zinc and copper was observed for as plated specimens, while alloying of zinc and copper at the interface was detected after annealing at 180 °C for 1 h. Electroplated zinc diffused into the copper foil during the 180 °C-annealing and the corrosion potential of the anodic polarization curve indicated the condition of the alloy surface. The annealing effect of 4 nm- and 25 nm-zinc electroplated copper specimens could be related to the results of electrochemical measurement.     

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.     

In situ gravimetry of nickel thin film during potentiodynamic polarization in acidic and alkaline sulfate solutions

The passivation process of nickel thin films during potentiodynamic polarization in acidic and alkaline sulfate solutions was analyzed by an electrochemical quartz crystal microbalance (EQCM) to separate the partial current density of nickel dissolution through the passive film, i_Ni²⁺, and the partial current density of film growth, i_O^2-. The values of i_Ni²⁺ and i_O^2- during potentiodynamic polarization (20 mV s⁻¹) in the passive potential region could be separated by comparing the mass change rate and net polarization current as a function of electrode potential. It is found that i_Ni²⁺ is larger than i_O^2- in pH 3.0, 0.5 M sulfate solution, while the situation reverses in pH 12, 0.5 M sulfate solution. The sulfate concentration dependences of i_Ni²⁺ and i_O^2- in pH 3.0, sulfate solution were significant as compared to those in pH 12, sulfate solution.     

Streaming potential measurements on stainless steels surfaces: evidence of a gel-like layer at the steel/electrolyte interface

Electric charges at the surface of a passive stainless steel are generally considered as concentrated either in the passive film itself, or at the metal/passive film interface, or in the electrical double layer at the film solution interface. Rest potential time dependence after immersion of a passive surface in aqueous electrolytes suggests however that slow processes occur in the onset of the surface charge. Specific experiments, such as streaming potential measurements and electrochemical impedance spectroscopy in a thin electrolyte cell, were carried out for understanding better this phenomenon. An AISI 304 type austenitic stainless steel with polished or bright annealed surface finishes was immersed in NaCl aqueous solutions with various pH and chloride concentrations. The streaming potential time evolution shows two steps: a first rapid one (∼2 min) is attributed to the onset of the surface charge. The second step is much slower (approximately several hours) and possibly due to an interphase layer between the passive film and the solution. Following this idea, the whole kinetics is controlled by cation migration across the interphase when the pH is larger than the isoelectric pH (pH_iep), while chloride ions are incorporated in the interphase when pH < pH_iep. Impedance measurements allow determining both the kinetics of charge transport and the thin cell conductivity. When glass is used as reference material for the cell walls instead of stainless steel, the Nyquist plots show a high-frequency response. For stainless steel cell walls, a low-frequency response is observed, attributed to a slow charge reorganisation inside the interphase layer. The charge distribution at metal/electrolyte interface is discussed in terms of a gel-like layer which possibly takes place at the passive film/electrolyte interface.     

Corrosion protection of iron by polypyrrole modified by copper using the cementation process

Polypyrrole (PPy) coatings have been deposited on iron from aqueous oxalic acid solution at different current densities. The polymer deposit obtained at a current density of 2 mA cm⁻² yields strongly adherent and smooth PPy layers. The modification of the film by incorporation of copper microparticles using the cementation process was applied. The resulting PPy/Cu film electrodes were characterized by scanning electron microscopy and EDX analysis. The protective performance against corrosion of these films is evaluated by using open circuit potential monitoring in highly corrosive solution (3% NaCl + HCl, pH 1). The results obtained were promising in the protection against corrosion.     

Photovoltaic properties of benzotriazole containing alternating donor–acceptor copolymers: Effect of alkyl chain length

A series of variable alkyl chain length substituted donor–acceptor (D–A) conjugated polymers with thiophene ring as the donor and benzotriazole moiety as the acceptor has been investigated in bulk heterojunction solar cells. The optical and electrochemical properties showed that the absorption onsets and the energy levels of the copolymers were not affected by alkyl substitution revealing 1.9 eV of optical band gap. The morphologies of the blend film can be fine-tuned by increasing the chain length attached to the benzotriazole unit. Photovoltaic devices were fabricated using (6,6)-phenyl-C₆₁-butyric acid methyl ester (PC₆₀BM) and (6,6)-phenyl-C₇₁-butyric acid methyl ester (PC₇₀BM) as the acceptors. The maximum performance was achieved with a V_oc of 0.75 V, J_sc of 3.70 mA/cm², FF of 45% and a PCE of 1.23% for the PTBT-DA10:PC₇₀BM device using 1:4 w/w ratio in chlorobenzene (CB).     

Effects of pH and chloride concentration on pitting corrosion of AA6061 aluminum alloy

Effects of pH solution and chloride (Cl⁻) ion concentration on the corrosion behaviour of alloy AA6061 immersed in aqueous solutions of NaCl have been investigated using measurements of weight loss, potentiodynamic polarisation, linear polarisation, cyclic polarisation experiment combined with open circuit potential transient technique and optical or scanning electron microscopy.The corrosion behaviour of the AA6061 aluminum alloy was found to be dependant on the pH and chloride concentration [NaCl] of solution. In acidic or slightly neutral solutions, general and pitting corrosion occurred simultaneously. In contrast, exposure to alkaline solutions results in general corrosion. Experience revealed that the alloy AA6061 was susceptible to pitting corrosion in all chloride solution of concentration ranging between 0.003 wt% and 5.5 wt% NaCl and an increase in the chloride concentration slightly shifted both the pitting E_pit and corrosion E_cor potentials to more active values. In function of the conditions of treatment, the sheets of the alloy AA6061 undergo two types of localised corrosion process, leading to the formation of hemispherical and crystallographic pits.Polarisation resistance measurements in acidic (pH = 2) and alkaline chloride solutions (pH = 12) which are in good agreement with those of weight loss, show that the corrosion kinetic is minimised in slightly neutral solutions (pH = 6).     

Characterization of corrosion of X70 pipeline steel in thin electrolyte layer under disbonded coating by scanning Kelvin probe

Scanning Kelvin probe technique was used to characterize the electrochemical corrosion behavior of X70 steel in a thin layer of near-neutral pH and high pH solutions, respectively. Results demonstrate that passivity can be developed on steel in the near-neutral pH solution layer as thin as 60 μm, which is attributed to the fact that Fe²⁺ concentration in aqueous phase could reach saturation in the thin solution layer. The solubility of FeCO₃ is reached to drop out of solution as a precipitate. With the increase of solution layer thickness, it becomes more difficult for Fe²⁺ concentration to reach saturation. Consequently, the passivity cannot be maintained, and the steel shows an active dissolution state. Anodic dissolution rate of steel increases with the immersion time. The electrochemical polarization behavior of X70 steel in high pH solution is approximately independent of the solution layer thickness and immersion time. In thin solution layer, diffusion and reduction of oxygen dominate the cathodic process, as demonstrated by the presence of cathodic limiting diffusive current. In the bulk solution, the absence of limiting diffusive current density in cathodic polarization curve indicates that the main cathodic reaction is reduction of H₂CO₃ and , and the formed film is thus mainly FeCO₃.     

In situ STM study of the duplex passive films formed on Cu(1 1 1) and Cu(0 0 1) in 0.1 M NaOH

In situ electrochemical scanning tunneling microscopy (ECSTM) investigations of the anodic Cu(I)/Cu(II) duplex passive layers grown on Cu(1 1 1) and Cu(0 0 1) in 0.1 M NaOH are reported. The outer Cu(II) part of the duplex film formed on both substrates is crystalline with a terrace and step topography. The observed lattices are consistent with a bulk-like terminated CuO(0 0 1) surface on both substrates. This common crystallographic orientation is explained by the hydroxylation of the otherwise polar and unstable oxide surface at the passive film/electrolyte interface. The epitaxy of the oxide layers is governed by the parallel alignment of the close packed directions of the CuO outer layers and Cu₂O inner layers on both substrates. A granular and amorphous layer covering the crystalline CuO(0 0 1) oxide has been observed on Cu(0 0 1) but not on Cu(1 1 1). It is assigned to a film of copper hydroxide corrosion products formed by a dissolution-precipitation mechanism. Its absence on the passivated Cu(1 1 1) surface is explained by the higher stability of the Cu₂O(1 1 1) precursor oxide formed on this substrate in the initial stages of growth of the duplex passive film, resulting in a lower amount of dissolved copper.     

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.     

Surface characteristics and corrosion behavior of Ti-Al-Zr alloy implanted with Al and Nb

Ti-Al-Zr alloys were implanted with Al and Nb to doses ranging from 1 × 10¹⁷ to 1 × 10¹⁸ ions cm⁻². The valence states of element on the sample surfaces were analyzed by X-ray photoelectron spectroscopy (XPS). Glancing angle X-ray diffraction (GAXRD) was employed on the as-implanted specimens to understand phase formation. X-ray diffraction (XRD) measurement revealed α-Ti on Al-implanted samples and (α + β)-Ti on Nb-implanted samples. The tendency was observed in increasing corrosion resistance from α- toward (α + β)-phase. In deaerated 5 M HCl, the ion-implanted Ti-Al-Zr surface containing Nb-stabilized β-phase was spontaneously passive, while Al-implanted surface displaying an active/passive behavior. In the aerated solution with pH = 10, all the implanted surfaces are passive. Enhanced reoxidation was confirmed on implanted surfaces by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) analysis. The corrosion in the solution with pH = 10 was governed by a predominantly TiO₂ surface film. The cathodic kinetics was seen to affect the corrosion behavior in 5 M HCl.     

Copper modified chitosan for protection of AA-2024

The aim of this study is to examine chitosan, which is a good film former, as a corrosion protective coating for AA-2024-T3 aluminium alloy. The aluminium samples were first anodized to increase adhesion of the subsequently dip coated film from a chitosan-acetic acid solution. To further increase the protective ability of the chitosan coating, the coated samples were immersed in a copper ion solution for 24 h. The copper salts used were sulphate and acetate. The chitosan membranes exposed to copper ion solutions revealed a reduced permeability in comparison with the unexposed samples, and an increase in stability in aqueous solutions, as revealed by a steady state and a high open circuit potential in borax solution. From UV-Vis spectroscopic measurement of the film on ITO glasses, the reduction in permeability of the chitosan film modified by copper ions appears to be associated with copper cross linking within the chitosan structure.