Ranko Babić

Impedance and photoelectrochemical study of surface layers on Cu and Cu-10Ni in acetate solution containing benzotriazole

Abstract The electrochemical behaviour of Cu and Cu–10Ni alloy in 1 M sodium acetate solution, pH 5.8 without and in the presence of benzotriazole (BTAH) was investigated by cyclic voltammetry, photopotential measurements and impedance spectroscopy. Both polarization and impedance studies clearly show that BTAH forms the multilayer structure Cu/Cu 2 O-Cu(I)BTA on the electrode surface at a higher concentration of the inhibitor ( c BTAH ≥1 mM) and at longer immersion time. At low inhibitor concentration and a shorter immersion time molecules of the inhibitor are adsorbed chemically on the electrode surface. Several important properties of the adsorbed layer and the passivated films were determined from the impedance spectra. The system parameters obtained by a nonlinear fit procedure are discussed in terms of the model used. The results indicate that the surface film was of a dielectric nature. Its thickness and protection against corrosion increase with increasing inhibitor concentration and/or ageing. The adsorptive behaviour of BTAH on the electrode surface follows a Langmuir-type isotherm with the free energy of adsorption, Δ G =−36.7 kJ mol −1 . Photopotential measurements show that the surface layer formed on Cu in the presence of BTAH is stoichiometric, while the film on an alloy shows small non-stoichiometry, i.e. the excess of anion vacancies, n-type conductivity.

Spectrochemical Characterization of Benzotriazole on Copper

The spectroelectrochemical behavior of Cu in 1 M sodium acetate solution, pH 5.8, alone and in the presence of benzotriazole (BTA) was investigated by cyclic voltammetry, impedance spectroscopy, and Raman spectroscopy. Impedance spectra are characterized by two time constants relating to charge transfer and transport of copper ions through the surface film, the latter being the rate-determining factor. The finite diffusion impedance is analyzed using a diffusion factor (B), which is a function of the diffusion layer thickness (d) and the diffusion coefficient (D f ) or Cu + species. The analysis suggests that changes in the film thickness can be monitored in situ by impedance spectroscopy. The values of D t and concentration of Cu + species (c f ) in the film formed in the presence of 1 M BTA were estimated to be of the order 10 -- 1 4 cm 2 s -1 and 10 -6 mol cm -3 , respectively. The results indicate that the film formed at higher inhibitor concentration and longer immersion time behaves almost like an ideal capacitor. Its thickness (up to 20 nm) and protection against corrosion increase by increasing the BTA concentration and immersion time. The results obtained by Raman spectroscopy confirm the model for the complex Cu(I)BTA in which overlap of Cu sp-hybrid atomic orbitals with the N-hybridized lone-pair atomic orbital occurs.

Copper corrosion at various pH values with and without the inhibitor

The inhibitory action of BTAH on copper was investigated in 1 M sodium acetate solution in the pH range 4–10, using cyclic voltammetry and impedance spectroscopy. Cyclic voltammetry showed that the rearrangement of the surface oxide layer in the presence of BTAH is very fast in slightly alkaline solutions, while it is time- and concentration-dependent in neutral and slightly acidic solutions. The adsorption behaviour of BTAH on the electrode surface at c(BTAH) ≤ 0.5 mM followed a Flory–Huggins adsorption isotherm with ΔG∘ ranging from −30.0 to −39.0 kJ mol−1, depending on the pH. Impedance spectra were characterized by two time constants relating to the charge transfer and transport of copper ions through the oxide layer, the latter being the rate determining step. These enabled the determination of important properties of the adsorbed layer and the passivated film. The results indicate that the surface layer is of dielectric nature, and its protection increases with increasing inhibitor concentration and solution pH. The finite diffusion impedance was analysed using a diffusion factor B, and the values of the diffusion coefficient and concentration of copper species in the film were estimated.

Copper Protection by a Self-Assembled Monolayer of Alkanethiol Comparison with Benzotriazole

Self-assembled monolayers (SAMs) formed by the adsorption of alkanethiols onto copper is a simple method for producing coatings that can protect the metal against oxidation and corrosion. However, a contradiction regarding the influence of oxygen on the SAMs formation and barrier properties is still present. In this work the self-assembled monolayers of dodecanethiol were formed on the copper substrates from ethanolic solutions of dodecanethiol with and without the presence of dissolved oxygen. The protecting properties of monolayers, were studied in a sodium acetate solution with a pH of 6 using cyclic voltammetry and electrochemical impedance spectroscopy. The effect of exposing samples, prepared in the deoxygenated solutions, to air was also studied to examine the decrease in the protecting properties of the SAMs against copper corrosion. The protection efficiency of the dodecanethiol SAMs was compared with those of benzotriazole which is known as the best inhibitor for copper corrosion.

Impedance investigation of corrosion inhibition of armco iron by thiourea

The inhibitive action of thiourea on the corrosive behaviour of ARMCO iron was investigated in deaerated 0.5 M H2SO4 solution, by means of electrochemical impedance spectroscopy. The inhibitor effectiveness increases with concentration, reaches a maximum (at about 1 mm) and then decreases. The adsorptive behaviour of thiourea on the electrode surface up to its peak follows a Frumkin-type isotherm with lateral repulsion, where the molecules are vertically adsorbed on the iron surface via the sulfur atom. Thiourea acts as a mixed inhibitor up to the critical concentration. It decreases the dissolution of iron and the hydrogen evolution reaction by blocking the electrode surface. The free energy of adsorption ΔGad = −39 kJ mol−1 and the attraction constant a = −4.4.

A Study of Copper Passivity by Electrochemical Impedance Spectroscopy

In situ electrochemical impedance spectroscopy was used to study the characteristics of the passive film formed potentiodynamically on copper, in slightly alkaline solution. This film has semiconducting properties A strong correlation was established between the impedance and the changes in the composition and structure of the passive film. Several parameters were examined, such as: the ionic resistivity, ρ ox of ∼10 10 Ω cm, the dielectric constant, e ox of ∼105, and the concentration of charge carriers of 10 20 cm -3 .

Impedance spectroscopic study of aluminium and Al-alloys in acid solution: inhibitory action of nitrogen containing compounds

The adsorption behaviour of triethanolamine (TEA) on aluminium, AlMgSi and AlZnMg alloys covered with naturally formed oxide films was investigated in 0.5 M NaCl solution, pH 1.3, by means of potentiodynamic and electrochemical impedance spectroscopy techniques. The results of polarization measurements show that in all cases the addition of TEA induces a decrease in the cathodic currents without affecting the anodic polarization behaviour, and, accordingly, TEA can be treated as a cathodic type inhibitor. The adsorption behaviour of TEA on the electrode surface follows a Frumkin isotherm with constants:a = 1.74,B = 18.41 dm3 mol−1. The results of impedance measurements presented in Nyquist plots show a high frequency capacitive loop related to the dielectric properties of the oxide film and a low-frequency inductive part which was determined by the faradaic process and attributed to the localized corrosion.

Corrosion protection of aluminium in acidic chloride solutions with nontoxic inhibitors

Corrosion kinetics of 99.6% aluminium covered by a thin spontaneously formed oxide film in hydrochloric acid solution with and without the presence of substituted N-aryl pyrroles was studied using electrochemical impedance spectroscopy and quasi steady-state polarization. Measurements were performed on a rotating disc electrode in an argon-deaerated solution in the temperature range 20 to 50°C. The addition of inhibitor considerably increases overvoltage of the cathodic process (HER) and shifts Ecorr to negative potential values. The activation energy of the hydrogen evolution reaction was Ea=50±5kJmol−1 and was not affected by the presence of inhibitor. The inhibitory action occurs by π-bonding between the adsorbed inhibitor molecules and the electrode surface. The electrode coverage follows the Langmuir adsorption isotherm with an adsorption equilibrium constant K=1.1–2.64×105dm3mol−1. The adsorption of organic compound prevents the adsorption of chloride ions and slow down the rate of corrosion.

Semiconducting properties of passive films on AISI 304 and 316 stainless steels

Abstract Passive films on AISI 304 and 316 stainless steels in a near-neutral 0.5 M NaCl solution were studied using potentiodynamic, impedance and photoelectrochemical techniques. The results obtained indicate that passive films on both steels show the characteristics of an amorphous or disordered n-type semiconductor. The passive film on molybdenum-containing stainless steel has a lower donor concentration than that on 304 stainless steel. During the ageing process the donor concentration in passive films on both steels decreases. The shift of the Mott-Schottky line with pH change and consequently the pH dependence of the flat-band potential is assumed to be caused by an acid-base equilibrium established at the passive film/solution interface. Potential dependence of the optical gap value is observed and is interpreted on the basis of the passive film composition.

Characterization of anodic films on lead and lead alloys by impedance spectroscopy

Abstract The behaviour of lead and lead-antimony binary alloys with 1.3–4.5 wt.% antimony was investigated in the lead sulfate and lead oxide potential regions by means of cyclic voltammetry and electrochemical impedance spectroscopy. The impedance data show that the inner PbO barrier layer is formed beneath the initially grown PbSO 4 porous layer at potentials positive to −0.2 V versus SCE. The antimony content influences the characteristics of the anodic layer by decreasing its resistance and increasing its capacity. These changes were observed both on the lead sulfate and especially the lead oxide layers. With increased anodic polarization, the film resistance increases as well while the capacity shows the opposite change.