Mirjana Metikoš-Huković

Passive film on orthopaedic TiAlV alloy formed in physiological solution investigated by X-ray photoelectron spectroscopy

The passive film formed by electrochemical oxidation on TiAlV alloy in physiological solution was studied using X-ray photoelectron spectroscopy (XPS) and electrochemical impedance spectroscopy (EIS). The alloy was polarised at different oxidation potentials in the electrochemical chamber attached to the spectrometer. Thus the composition of the layer formed by oxidation was analysed by XPS without prior exposure to air (quasi-in situ). The oxide layer was predominantly TiO2, which contained a small amount of suboxides TiO and Ti2O3 closer to the inner metal/oxide interface. With increasing potential the content of Ti4+ species increased and that of Ti3+ and Ti2+ decreased. The content of titanium in TiO2 was lower than theoretically predicted due to the incorporation of Al2O3 in TiO2 matrix. Vanadium oxide was not identified by XPS. Angular resolved XPS analysis confirmed that Al2O3 is located mainly at the outer oxide/solution interface. The thickness of the oxide layer was dependent on the oxidation potential and after oxidation at 2.5 V reached 9 nm. EIS measurements were used to in situ characterise electronic properties of passive films over seven decades of frequency. A link between electronic, electrochemical and physiochemical properties was established.

An in vitro study of Ti and Ti-alloys coated with sol-gel derived hydroxyapatite coatings

Electrochemical–corrosion properties of Ti, Ti6Al6Nb and Ti6Al4V implant materials coated with calcium phosphate (CaP) coatings were investigated in vitro at the open circuit potential using non-destructive electrochemical impedance spectroscopy (EIS) technique in simulated physiological-Hanks Balanced Salt Solution (HBSS). Characterization of the structure and composition of CaP coatings obtained by the sol–gel method was performed using X-ray diffraction analysis. The interpretation of the EIS results was based upon a two-layer model of the surface film consisting of an inner barrier TiO2 (CaTiO3) layer and the outer porous hydroxyapatite (HAP)+β-tricalcium phosphate (β-TCP) layer, described by using the high frequency time constant (τ1HF) and the low frequency time constant (τ2LF), respectively. Spontaneously passivated surfaces of naturally grown surface films on all three substrates in HBSS were used for reference. The chemical composition of the substrate as well as the composition and crystallinity of the CaP coating have a direct influence on electrochemical–corrosion properties of the implant materials under in vitro conditions. Well-crystallized HAP and β-TCP exhibited a beneficial corrosion protection effect on the substrate during prolonged exposure to HBSS. In the case of poorly crystallized coatings containing a greater amount of carbonate incorporated in the structure of HAP, the total impedance of the system markedly changed with prolonged exposure to physiological solution due to degradation of the coating.

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.

The study of aluminium corrosion in acidic solution with nontoxic inhibitors

The inhibitory activity of some substituted N-arylpyrroles on aluminium corrosion in hydrochloric acid was studied in relation to inhibitor concentration, using potentiodynamic and impedance spectroscopy techniques. All investigated compounds were found to act as cathodic-type inhibitors and inhibition was ascribed to the adsorption of inhibitor onto the electrode surface. The inhibiting efficiency of the additives depended on the inductive power of the groups attached to the benzene and/or pyrrole ring. The carbaldehyde group showed better inhibiting power due to additional condensation on the electrode surface. The impedance results analysed in terms of the polarization resistance showed that the EIS technique can be successfully applied in the determination of corrosion resistance in systems where the corrosion kinetics are not simple.

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 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.

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.

Electrodeposition of thin sulfide films: nucleation and growth observed for Bi2S3

The potentiostatic pulse technique proved to be the most powerful electrochemical technique for in situ studies of the early stages of Bi2S3 electrodeposition on bismuth. The current–time response recorded at the overpotentials in the vicinity of Er (Bi2S3/Bi) in dependence of hydrogen sulfide ion concentrations, was described by a theoretical expression for three-dimensional progressive nucleation and growth under diffusion control. Through the application of relations which hold true for such a nucleation model, the following parameters were determined: (i) the anodic nucleation potential (EAN); (ii) the rate of nucleation (AN∞); (iii) the diffusion coefficient (D); and (iv) the density of the growing sites (Ns).

Electrocatalytic behavior of the Co33Zr67 metallic glass for hydrogen evolution

Amorphous Co33Zr67 alloy, prepared by rapid solidification of its components (Co, Zr) in an argon atmosphere, was investigated in view of its possible application as electrocatalytic material for the hydrogen evolution reaction (h.e.r.). Electrocatalytic efficiency was evaluated on the basis of electrochemical and impedance measurements carried out in deaerated 1 M NaOH solution. The results were compared with polycrystalline Co and Zr metals. The Tafel slope, bc and the value of exchange current density, j0 confirmed rather good electrocatalytic properties of Co; on the contrary, pure Zr exhibited very poor activity for the h.e.r. which was influenced by the presence of a ZrO 2 surface layer due to high affinity of Zr for oxygen. Improved electrocatalytic performances were obtained after the as quenched Co33Zr67 samples were chemically pretreated in HF solution. The true kinetic parameters of these electrodes for the hydrogen evolution reaction resembled that of Co, but the stability and activity in the highest state exceeded those of pure polycrystalline Co electrode. Experimental results of hydrogen evolution kinetics on the Co33Zr67 alloy were discussed using known electronic structure of Co‐Zr amorphous alloys, ionicity difference between Co and Zr, as well as the free energy of adsorption and the bond strength of hydrogen adsorbed on Co.

The effect of alloying with antimony on the electrochemical properties of lead

The electrochemical behaviour of lead, antimony and lead-antimony binary alloys has been studied as a function of sulfuric acid and antimony concentrations in the lead alloy. The investigation was performed by means of cyclic voltammetry and impedance spectroscopy methods. Cyclic voltammetry, performed between the hydrogen and oxygen evolution and over narrower regions of potential coupled with systematic variation of the scan rates and the positive or negative reversal potential, revealed more details on the oxidation and reduction processes in the potential region of Pb(II)-, Pb(IV)- and Sb(III)-containing species which give further insight into the nature of the reactions of the lead/acid battery. The impedance measurements performed in the potential range of lead oxide, in which antimony oxidation in the alloys takes place, show the decrease in film resistance with increasing antimony content.