The electrochemical interface between copper(111) and aqueous electrolytes

The electrochemical double layer between Cu(111) electrodes and aqueous electrolytes (F⁻ and SO²⁻₄ at various pH values) was studied by means of linear scan voltammetry and ac impedance measurements. It is found that electrochemisorption of oxygen species proceeds on the Cu(111) surface in the potential regions more negative than the electrodissolution potential of copper. The adsorption-desorption kinetics are analysed; the anodic and cathodic symmetry coefficients are found to be equal (α = β = 0.3), and the standard rate constant is k° = 4 × 10⁻¹⁰cm s⁻¹.     

Indole‐3‐acetic acid and N‐acetyltryptophan corrosion inhibition effects on mild steel in 1 M hydrochloric acid solution

Corrosion inhibition of indole‐3‐acetic acid and N‐acetyl tryptophan on carbon steel was investigated using polarization and electrochemical impedance spectroscopy (EIS). Polarization results revealed that corrosion inhibitors could reduce the rate of cathodic and anodic reactions on metal surface. EIS analysis showed inhibition efficiency of indoles increases by increasing the inhibitor concentration. The maximum inhibition efficiency was 97% and 80% in solutions containing 10 mM indole‐3‐acetic acid and 10 mM N‐acetyl tryptophan, respectively. The adsorption of inhibitors was found to follow Langmuir isotherm. Adsorption and film formation of inhibitors on the metal substrate were confirmed by calculating thermodynamic adsorption parameter (ΔG⁰_ads) and characterization of exposed metals' surface through contact angle measurements. Copyright © 2014 John Wiley & Sons, Ltd.     

Adsorption characteristics of metal-EDTA complexes onto hydrous oxides

The adsorption characteristics of a variety of metal-EDTA complexes onto hydrous oxides, principally aluminum oxide (γ-Al₂O₃), were examined in aqueous solution. Adsorption of these complexes increased with increasing proton concentration due to the formation of surface complexes between EDTA and the surface hydroxo groups, specifically the AlOH₂⁺ surface groups. The pH-dependent adsorptive behavior and the magnitude of adsorption of the “free” EDTA species were similar to those of the metal complexes. The results also showed that the adsorption of “free” EDTA was exothermic, while the adsorption of Ni(II)-EDTA complexes was endothermic in the lower pH region (3.5) and exothermic at higher pH values (6.0). This implied that the surface preferred the NiHEDTA⁻¹ species rather than the NiEDTA⁻² species. Specific adsorption of the metal complexes was evidenced by the charge reversal exhibited by the γ-Al₂O₃ particles at the highest surface loadings. A quantitative model was formulated based on the pH-dependent speciation of the oxide surface, speciation of the metal complexes in solution, and ζ potential measurements. This model proved valid over a wide range of pH (3–10) and for both high (>50% coverage) and low (<10% coverage) surface loadings.     

An Integrated Experimental and Theoretical Studies on the Corrosion Inhibition of Carbon Steel by Harmal Extracts

The corrosion inhibition effect of the three extracts from Harmal roots (HRE), leaves (HLE), and flowers (HFE) were studied for carbon steel corrosion inhibition in 0.25 M H₂SO₄ solution. The electrochemical impedance study indicated that the three types of extracts decreased corrosion effectively through a charge transfer mechanism. Harmal roots and leaf extracts showed inhibition values of 94.1% and 94.2%, while it was 88.7% for Harmal flower extract at the inhibitor concentration of 82.6 ppm. Potentiodynamic polarization data revealed that Harmal extracts acted through predominant cathodic type inhibition. Both the corrosion current density and corrosion rate decreased significantly in the presence of Harmal extracts compared to blank solution. The corrosion rate (mpy) value was 63.3, 86.1, and 180.7 for HRE, HLE, and HFE, respectively. The adsorption-free energy change ΔG_ads (kJ·mol⁻¹) values calculated from the Langmuir adsorption isotherm plots were for HRE (−35.08), HLE (−33.17), and HFE (−33.12). Thus, corrosion inhibition occurred due to the adsorption of Harmal extract on the carbon steel surface via the chemisorption mechanism. Moreover, a computational investigation using B3LYP/6-311G++(d,p) basis set in both gaseous and aqueous phases was performed for the major alkaloids (1–8) present in the Harmal extract.     

Voltammetric determination of quercetin at a multi-walled carbon nanotubes paste electrode

Quercetin can effectively accumulate at multi-walled carbon nanotubes-paraffin oil paste electrodes (CNTPE) and cause a sensitive anodic peak at around 0.32 V (vs. SCE) in a 0.10 M phosphate buffer solution (pH = 4.0). Under optimized conditions, the anodic peak current is linear to quercetin concentration in the ranges of 2.0 × 10^− 9−1.0 × 10^− 7 M and 1.0 × 10^− 7−2.0 × 10^− 5 M, and the regression equations are i_p (μA) = 0.0017 + 0.928c (μM, r = 0.999) and i_p (μA) = 0.183 + 0.0731c (μM, r = 0.995), respectively. This paste electrode can be regenerated by repetitively cycling in a blank solution for about 2 min. A 1.0 × 10^− 6 M quercetin solution is measured for 10 times using the same electrode regenerated after every determination, and the relative standard deviation of the peak current is 1.7%. The method has been applied to the determination of quercetin in hydrolysate product of rutin and the recovery is 99.2–102.6%. In comparison with graphite paste electrode, carbon nanotubes-nujol paste electrode and carbon nanotubes casting film modified glassy carbon electrode, the CNTPE gives higher ratio of signal to background current and better defined voltammetric peak.     

The influence of different variables on the electrochemical behavior of mild steel in circulating cooling water containing aggressive anionic species

Cyclic voltammetric, potentiodynamic anodic polarization and current–time transient studies were carried out on mild steel in circulating cooling water containing Cl⁻ and SO₄⁻² ions under the effect of different variables such as coolant flow, the availability of oxygen, cooling system temperature, and cooling system pH. The anodic excursion span of mild steel in cooling corrosive solution was characterized by the occurrence of a well-defined anodic peak (A1), while the reverse sweep was characterized by the appearance of two cathodic peaks (C1 and C2). The presence of Cl⁻ and SO₄⁻² ions in cooling water enhance the active dissolution of mild steel and tend to breakdown the passive film and induce pitting attack. The data reveal that increasing flow rate and temperature of cooling solution enhances the anodic peak current density (j _A1) and shifts the pitting potential (E _pit) towards more active values. It is seen that the peak current density of the anodic peak A1 increases and the pitting potential (E _pit) displaced in the noble direction in the aerated solution compared that in de-aerated solution. The pitting corrosion of mild steel by Cl⁻ and SO₄⁻² ions initiates more readily in acidic medium (pH 2.0). It was found that the incubation time (t _i) increase and in turn the pitting corrosion decrease in the order: pH 10 > pH 6.8 > pH 2.0.     

Adsorption Behavior and Inhibition Corrosion Effect of Sodium Carboxymethyl Cellulose on Mild Steel in Acidic Medium

The effect of sodium carboxymethyl cellulose (Na-CMC) on the corrosion behavior of mild steel in 1.0 mol·L⁻¹ HCl solution has been investigated by using weight loss (WL) measurement, potentiodynamic polarization, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) methods. These results showed that the inhibition efficiency of Na-CMC increased with increasing the inhibitor concentration. Potentiodynamic polarization studies revealed that the Na-CMC was a mixed type inhibitor in 1.0 mol·L⁻¹ HCl. The adsorption of the inhibitor on mild steel surface has been found to obey the Langmuir isotherm. The effect of temperature on the corrosion behavior of mild steel in 1.0 mol·L⁻¹ HCl with addition of 0.04% of Na-CMC has been studied in the temperature range of 298–328 K. The associated apparent activation energy (E^*_a) of corrosion reaction has been determined. Scanning electron microscopy (SEM) has been applied to investigate the surface morphology of mild steel in the absence and presence of the inhibitor molecules.     

Experimental and theoretical studies of carbon steel corrosion protection in phosphoric acid solution by expired lansoprazole and rabeprazole drugs

The effects of expired lansoprazole and rabeprazole on the corrosion protection of carbon steel in phosphoric acid (3.0 ?M) solution were examined by Tafel polarization and electrochemical impedance spectroscopy (EIS). Lansoprazole and rabeprazole concentrations (0.5, 1.0, 5.0 and 10 ?mM) in acid solution were raised, which improved corrosion prevention. Both lansoprazole and rabeprazole as the mixed inhibitors retarded the anodic and cathodic processes, as indicated by polarization data. With the increasing temperature in the range of 25–55 ?°C, the inhibition efficiency drops from 92.9% to 69.3% for lansoprazole and from 94.8% to 74.2% for rabeprazole. The major decrease in the inhibition efficiency with ascending temperature proved the physisorption of the drugs. The activation energies for carbon steel corrosion in H₃PO₄solution were enhanced from 41.6 ?kJ ?mol^?1 to 81.9 ?kJ.mol^?1and 85.9 ?kJ ?mol^?1 for lansoprazole and rabeprazole, respectively. The influence of temperature on the corrosion process of carbon steel in the acid medium was used to derive the thermodynamic quantities of corrosion. The adsorption of both lansoprazole and rabeprazole on carbon steel followed the Langmuir adsorption isotherm. The polarization data yielded outcomes that were consistent with the results arising from impedance measurements. The theoretical study of both lansoprazole and rabeprazole was done by a density functional theory (DFT) approach to realize the effects of molecular structure on their inhibitive action. Both lansoprazole and rabeprazole contain a higher E_HOMO, a lower E_LUMO and a lower energy gap than some inhibitors earlier reported as good corrosion inhibitors in the literature.     

An in situ STM study on the long-range surface restructuring of Au(1 1 1) in a non-chloroaluminumated ionic liquid

We report an in situ STM study of a potential-dependent long-range surface restructuring of Au(1 1 1) electrode in neat 1-butyl-3-methylimidazolium tetrafluoroborates (BMIBF₄) ionic liquid. Au(1 1 1) undergoes a significant long-range surface restructuring upon cathodic excursion to −1.0 V vs. Pt quasi-reference. The restructuring involves the formation of tiny pits, which then develops into a stable worm-like network with an average width of the network grids 2 nm. Electrochemical annealing occurs at the cathodic limit with the presence of a reduction product of cation BMI⁺. A smooth surface is recovered with the appearance of the typical (√3 × 22) reconstruction of Au(1 1 1). The surface restructuring is reestablished upon anodic excursion to −1.3 V after the adsorbed reduction product is oxidized. The long-range surface restructuring phenomenon is tentatively explained as a result of partial charge transfer to the weakly adsorbed BMI⁺, which reduces the metal–metal cohesive energy. In addition, the synergetic effect of the counter anion BF₄⁻ may also be involved. The results provide a knowledge of Au(1 1 1) electrode behavior in the neat ionic liquid and are beneficial to understanding in situ STM results involving surface morphological changes in such a media.     

Electrodeposition of lead on to a graphite probe for electrothermal atomic absorption spectrometry

A simple system for controlled potential electrodeposition on to a graphite probe electrode is described. Totally pyrolytic graphite was found to be better for electrodeposition than microporous glassy carbon or electrographite coated with pyrolytic graphite. Lead can be deposited by anodic and cathodic processes as PbO₂ and Pb, respectively. Potentials of + 1.2 to + 2.0 V were best for anodic deposition and – 0.8 to– 2.0 V were best for cathodic deposition. With an electrodeposition time of 120 s, AAS sensitivity gains of × 9 and × 3.5 were achieved for anodic and cathodic deposition, respectively, in comparison with the results obtained by direct injection of 20 1 sample volumes on to the probe. The lead cathodic process was unaffected by NaCl concentrations up to 10^–2 M, but only 10^–3 M NaCl could be tolerated by anodic deposition.     

Corrosion inhibition of carbon steel in hydrochloric acid 0.5 M by hexa methylene diamine tetramethyl-phosphonic acid

The efficiency of hexa methylene diamine tetra methyl-phosphonic acid (HMDTMP), as corrosion inhibitor for carbon steel in 0.5 M HCl, has been determined by gravimetric and electrochemical measurements. Polarization curves indicate that the compound is a mixed inhibitor, affecting both cathodic and anodic corrosion currents. Adsorption of HMDTMP derivatives on the carbon steel surface is in agreement with the Langmuir adsorption isotherm model, and the calculated Gibbs free energy value confirms the chemical nature of the adsorption. EIS results show that the charge in the impedance parameters (R_t and C_dl) with concentrations of HMDTMP is indicative. The adsorption of this molecule leads to the formation of a protective layer on carbon steel surface. The electrochemical results have also been supplemented by surface morphological studies.     

Effect of polarization on the electrode behavior and microstructure of (La,Sr)MnO<Subscript>3</Subscript> electrodes of solid oxide fuel cells

The electrode behavior and microstructure of freshly prepared (La_0.8Sr_0.2)_0.9MnO₃ (LSM) electrodes were investigated under various polarization conditions. The original, large agglomerates in freshly prepared LSM electrodes were broken down into sphere-shaped grains when exposed to cathodic or anodic current passage of 200 mA cm^–2 at 800 °C in air for 3 h. Microstructural changes under cathodic polarization could be related to the pronounced diffusion and migration of oxygen vacancies and Mn ions on the LSM surface and lattice expansion, while lattice shrinkage under oxidation conditions most likely contributes to the structural changes under anodic polarization. Such morphological changes were irreversible and were found to be beneficial to the performance of freshly prepared LSM electrodes. Freshly prepared LSM electrodes behaved very differently with respect to the cathodic and anodic current passage treatment.     

Experimental and theoretical studies on protecting steel against 0.5 M H2SO4 corrosion by new schiff base

In this study, a novel green corrosion inhibitor called 2,2'-((1Z,1′Z)-((piperazine-1,4-diylbis(2,1-phenylene))bis(methanylylidene))bis(azanylylidene)) (PMA) has been tested against corrosion of carbon steel in 0.5 M H₂SO₄. Quantum and electrochemical methods were used to evaluate PMA's ability to inhibit the deterioration of carbon steel in an acidic environment. The results revealed that PMA acted as a mixed inhibitor, primarily anodic, whose inhibition action was enhanced by increasing its concentration. At 298.15 K, the maximum efficiency was around 91% with 1 × 10^?3 M PMA in 0.5 M H₂SO₄. The results showed that the inhibition occurred due to adsorption of the PMA molecules on the surface. The adsorbed layer of PMA satisfied the Langmuir adsorption isotherm. The morphology of the surface was examined using scanning electron microscopy.     

Spectroelectrochemical study of the corrosion of a copper electrode in deaerated 1.0 M HCl solutions containing Fe(III): Effect of the corrosion inhibitor benzotriazole

The corrosion rate of a copper electrode in deaerated 1.0 M HCl by Fe(III) ions, in the absence and presence of benzotriazole (BTAH), has been evaluated through weight-loss experiments using a rotating disk electrode (RDE). The corrosion process is controlled by transport of the Fe(III) ions to the electrode surface both in the absence and presence of BTAH. The inhibiting action is initiated at BTAH concentrations around 10 mM and the Langmuir adsorption isotherm is obeyed in the BTAH concentration range from 10 to 45 mM with an apparent equilibrium adsorption constant of 10 M⁻¹. Above this concentration, the Langmuir plot is not obeyed due to the formation of a multilayer. The surface films formed during the corrosion process have been investigated by “in situ” and “ex situ” fluorescence and Raman spectroscopy and characterized as being composed of the polymeric [Cu(I)BTA] complex and [Cu(I)CIBTAH]₄, the former as an inner layer response for the corrosion inhibition process.     

Dissolved carbon dioxide effect on the behavior of carbon steel in a simulated solution at different temperatures and immersion times

Dissolved carbon dioxide effect on the behavior of carbon steel (0.4%carbon), in a simulated solution at different temperatures and immersion times, has been investigated using different techniques as potentiodynamic polarization, linear polarization resistance, and electrochemical impedance spectroscopy. The observation of the steel surface was done by scanning electron microscopy. All measurements reveal that the corrosion resistance is strongly dependent on both the temperature and immersion times. The corrosion resistance of carbon steel decreases in the solution considered as the temperature increases from 20?°C to 50?°C. Potentiodynamic polarization curves showed that cathodic and anodic current densities increase with the increased temperature. Besides, the study concluded that the addition of CO₂ gas to the simulated solution affects negatively the corrosion resistance in one hand and that, on the other hand, the higher the time of immersion the higher is the resistance to corrosion.     

Electrochemical study of the corrosion behaviour of carbon steel in fracturing fluid

Corrosion behaviour of carbon steel (K-55) in fracturing fluid was studied with a rotation cylinder electrode, under static and rotation conditions by means of several electrochemical techniques which are as follows: open circuit potential (OCP) decay, potentiodynamic polarisation and electrochemical impedance spectroscopy (EIS). The corrosion rate was determined by weight loss measurements. The electrode surface after a prefixed immersion time was characterised by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results indicated that carbon steel showed anodic dissolution behaviour that increased under rotating condition. The cathodic polarisation current density also increased with the electrode rotation due to the increased oxygen diffusion on the electrode surface. Two different oxide layers were formed: a dark, thin layer of magnetite tightly adhering to the electrode surface, characterised by localised corrosion spots, and a porous reddish layer of poorly adhering hematite (Fe₂O₃) and maghemite (γ-Fe₂O₃). Under higher rotation rate, the developed oxide layer was not so stable, owing to the shear stress induced between the solution and the specimen surface, enhancing the corrosion rate.     

Ni2+ cation and imidazole as corrosion inhibitors for carbon steel in sulfuric acid solutions

Abstract  

The effect of Ni²⁺ cation, imidazole, and mixtures of them on the corrosion behavior of carbon steel in 0.5 M H₂SO₄ solution was studied by using galvanostatic polarization, potentiodynamic anodic polarization, and weight-loss techniques. Ni²⁺ cation, imidazole, and mixtures of them provide a good protection to carbon steel against pitting corrosion in chloride-containing solutions. The inhibiting solutions were analyzed by using UV–Vis spectrophotometry. The inhibition was explained on the basis of formation of a complex between the two components. The inhibition mechanism was discussed in terms of the results derived from corrosion and UV–Vis spectrophotometric measurements as well as conductometric investigations.     

Pitting corrosion of zinc in alkaline medium by thiocyanate ions

This paper describes the use of potentiodynamic anodic polarization, cyclic voltammetry and chronoamperometry techniques in order to study the pitting corrosion susceptibility of a Zn electrode in KOH solutions containing KSCN as a pitting corrosion agent. Measurements were conducted under different experimental conditions. The results demonstrated that in the absence of KSCN, the anodic voltammetric response displays two anodic peaks prior to reaching the oxygen evolution potential. The first anodic peak A₁ is related to the electroformation of Zn(OH)₂. Peak A₁ is followed by a wide passive region which extends up to the appearance of the second anodic peak A₂. The latter is assigned to the formation of ZnO₂. Addition of SCN⁻ ions to the KOH solutions stimulates the anodic dissolution through peak A₁ and breaks down the passive layer prior to peak A₂. The breakdown potential decreases with an increase in SCN⁻ concentration and temperature, but increases with an increase in KOH concentration and potential scan rate. Successive cycling leads to a progressive increase in breakdown potential. The current/time transients show that the incubation time for passivity breakdown decreases slightly with increasing applied positive potential, SCN⁻ concentration, and temperature.     

Effect of the Electrode Potential on the Oxygen Reaction Rate in the Electrode System O2, Au/La0.88Sr0.12Ga0.82Mg0.18O2.85

The polarization dependences of a porous gold electrode in contact with a solid electrolyte of the composition La_0.88Sr_0.12Ga_0.82Mg_0.18O_2.85 are studied at 600–800°C and oxygen pressures of 2 × 10⁻²-1 atm. It is shown that the rate of cathodic reduction of oxygen out of the gas phase depends on the preliminary treatment of the sample. The activation energy is equal to 110–135 kJ mol⁻¹ at a low polarization. After increasing the polarization, the activation energy for the cathodic reduction of oxygen equals 75–85 kJ mol⁻¹ and depends on the oxygen pressure as a power function with a power index of 1/4. The rate of the anodic evolution of oxygen is dependent neither on the preliminary treatment of the sample nor on the oxygen pressure in the gas phase and the polarization curve has a characteristic segment, which corresponds to a limiting overvoltage.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 954–962.Original Russian Text Copyright © 2005 by Shkerin, Sokolova, Beresnev.     

Electrochemical kinetic analysis of a 1,4-hydroxynaphthoquinone self-assembled monolayer

Electroactive 5-hydroxy-3-hexanedithiol-1,4-naphthoquinone (JUG_thio) has been self-assembled on gold. Electrochemical results show the surface coverage is 2.2 × 10⁻¹⁰ mol cm⁻², which is consistent with a dense monolayer. The JUG_thio shows one quasi-reversible and stable voltametric wave in aqueous buffered solution. A kinetic analysis of the redox reactions involving both electron and proton transfer has revealed an unusual behaviour of this molecule due to the presence of the hydroxyl function in the vicinity of the quinone group. The apparent kinetic rate constant and the anodic coefficient transfer of this reaction depend on the pH. In acid medium, a classical concerted 2e⁻/2H⁺ mechanism is obtained. In basic medium (pH > 7), strong intramolecular hydrogen interactions between the quinone and the hydroxyl function have a strong influence on the redox kinetics. These results show that JUG_thio electroactivity is very sensitive to hydrogen interactions in neutral and basic pH solution and is able to act as sensitive layer for electrochemical biosensing.