C.A. Gervasi

Zinc-Rich Paints on Steels in Artificial Seawater by Electrochemical Impedance Spectroscopy

Abstract Electrochemical impedance spectroscopy (EIS) was applied over a wide frequency range to characterize the corrosion protection behavior by two types of zinc-rich paints (ZRP) (zinc-rich epo...

Potentiodynamic behaviour of tin in different buffer solutions

Abstract The anodic oxidation of tin in carbonate–bicarbonate solutions covering a wide range of pH and electrolyte composition has been studied by voltammetric techniques and scanning electron microscopy (SEM). The influence of switching potentials, potential scan rate, rotation speed and surface condition are reported. SEM micrographs of the electrode surface show considerable differences in the characteristics of the surface products, whether they were formed in the potential region of the electroformation of stannous oxide and hydroxide or Sn(IV)-containing species which dehydrates into the most stable species. From the dependence of the charges on the potential scan rate it may be inferred that a direct oxidation of Sn(0) to Sn(IV) exists besides the sequence Sn(0) to Sn(II), and Sn(II) to Sn(IV). The effect of the initial surface state on the anodic reactions is better recognized for a rotated electrode. Analysis of the first and second voltammetric cycles through the changes of the anodic current densities with rotation speed, suggests that the initial electrooxidation process at a freshly prepared electrode surface does not follow a dissolution–precipitation mechanism. The formation of soluble corrosion products is enhanced in the potential range of the secondary passivity as the ionic strength of the buffer increases.

An electrochemical impedance spectroscopy study of zinc rich paints on steels in artificial sea water by a transmission line model

Abstract Electrochemical impedance spectroscopy (EIS) in the 50 kHz–1 mHz frequency range was applied to characterize the corrosion protection behaviour of zinc rich ethyl silicate paints (ZRP) on steel in artificial sea water. The most accurate description of the experimental impedance spectra at the open circuit potential as a function of exposure time for different coating thicknesses, was obtained by introducing a dynamic system analysis based on the transmission line model and assuming cylindrical pores in the coating structure for the corresponding transfer function. Characteristic coating parameters of this type of ZRP during the galvanic protection period derived from nonlinear fit routines at different immersion times correlate well with the gradual coating deterioration. Results can be interpreted in terms of corrosion processes going on extensively through pores and cracks in the relatively thick ZRP coatings.

The electrochemical behaviour of cobalt in carbonate-bicarbonate solutions

Abstract The dissolution and passivation of polycrystalline cobalt electrodes in carbonate-bicarbonate solutions were studied at 25°C. The influence of the CO 3 2− /HCO 3 − concentration ratio and hydrodynamics on the electrodissolution of the base metal, on the formation of both the prepassivating and passivating surface layers and on the chemical dissolution of the prepassive films are considered. Data are discussed on the basis of the interaction between HCO 3 − ions and Co(II) anodic products in the surface layer.

Electrochemical preparation and characterization of polypyrrole/stainless steel electrodes decorated with gold nanoparticles.

The electrosynthesis and characterization of polypyrrole(PPy)/stainless steel electrodes decorated with gold nanoparticles and the performance of the composite electrode for sensing applications is described. PPy films were grown in potassium perchlorate and sodium salicylate solutions under comparable electropolymerization conditions. Polymer films prepared in the presence of perchlorate ions exhibited worm-like structures, whereas columnar structures were obtained in salicylate-containing solutions. Voltammetric response of PPy films prepared in salicylate solutions was more reversible. PPy films were decorated with gold nanoparticles obtained by a double step potentiostatic electrodeposition routine that allowed fine control of deposit characteristics. Analysis of deposits was performed by means of SEM and confocal Raman spectroscopy. The electrocatalytic activity of the Au/PPy electrodes was assessed for the electro-oxidation of hydrazine and hydroxylamine. Results showed a successful optimization of the route of synthesis that rendered nanocomposite electrode materials with promising applications in electrochemical sensing.

Estimating diffusion coefficients of probe molecules into polyelectrolyte brushes by electrochemical impedance spectroscopy.

Molecular transport through thin polymer films has become a subject with a variety of challenges and opportunities for chemists, physicists, and material scientists in recent years. The diffusion of probe molecules in and out of macromolecular environments plays a major role in the response of polymer-based sensor materials or the design of time-released drug delivery systems. Obtaining an improved understanding of the relevant dynamic phenomena, like transport of molecular probes, in boundary layers represents a crucial step to develop a clearer picture of the molecular transport processes taking place at interfaces modified with macromolecular assemblies. In this work, we present a new approach based on the derivation of the theoretical impedance transfer function to unambiguously describe the impedance response of gold electrodes modified with poly(methacryloyloxy)-ethyl-trimethyl-ammonium chloride (PMETAC) brushes. We demonstrate that this methodology not only enables the description of the experimental data but also provides insightful information about the dynamics of the diffusion of probe molecules inside the brush. More important, we show the capabilities of electrochemical impedance spectroscopy to gather information on a molecular transport process inside the brush under experimental conditions in which other electrochemical techniques are no longer applicable. As such, we consider that this experimental approach constitutes a new and powerful tool to estimate diffusion coefficients of probe molecules into interfacial macromolecular assemblies.

Investigations of the electroreduction process of anodic films grown on tin in carbonate-bicarbonate solutions

Combined voltammetry and potentiostatic current transient techniques have been employed to study the electroreduction process of composite surface layers anodically formed on high purity polycrystalline tin in carbonate-bicarbonate ion containing solutions. The dynamic system analysis performed by using parametric identification procedures and non-linear fit routines has demonstrated that data obtained under a wide variety of experimental conditions can be interpreted by taking into account the participation of various Sn(II)Sn(IV)-containing surface species. Thus, the electroreduction of passive layers formed at relatively low potentials can be explained through an instantaneous nucleation and 3D growth mechanism controlled by diffusion of OH− ions away from the reacting interface, whereas for surface layers produced at high positive potentials where the formation of SnO2 predominates, the electroreduction follows a progressive nucleation and 3D growth process under charge transfer control. The influence of anodizing time at different potentials as well as effects due to surface layer thickness can be discussed on the basis of electroreduction reaction models.

Characterization of passive films on tin through transient electrochemical techniques

Abstract Voltammetry and chronoamperometry were employed to derive mechanistic information about the electroreduction of anodic films on tin. This information proved useful to gain a deeper insight into the complex passivation process as well as into the passive layer changes generated by the anodizing procedure. Tin electrodes were anodized in carbonate–bicarbonate buffers covering a wide range of pH and electrolyte composition. Two cathodic peaks were detected in the voltammetric response and they were correlated with two maxima present in electroreduction current transients. The second electroreduction process corresponds to a surface species generated during the anodic potential bias at the beginning of the secondary passivity range. This process has distinct features and is dependent on anodizing time, solution agitation and ionic strength of the electrolyte.

An impedance spectroscopy study of the anodically formed barrier layer on aluminium substrates

Abstract Al 99.996 and Al-0.4% Mn specimens were anodically oxidized in a boric acid-borate solution (pH 7.4, 15°C). The electronic properties of the thin oxide films were investigated using electrochemical impedance spectroscopy in the potential range 0.3 V ⩽ E ⩽ 1.8 V. The impedance of the system is characterized by two capacitive contributions in the frequency range 0.1 Hz ⩽ f ⩽ 50 kHz. The dynamic characteristics of the electrochemical system are discussed in terms of a model which accounts for the presence of space charge and surface state effects.

A kinetic study of the electroreduction of anodically formed cobalt oxide layers

Abstract The kinetics of the electroreduction of anodically formed cobalt oxide layers in different carbonate-bicarbonate aqueous solutions were investigated using combined voltammetric and potential step techniques. The composition of the electrolyte was varied to cover wide pH and ionic strength ranges. The electroreduction reaction can be explained through a nucleation and three-dimensional growth process, involving cobalt phase formation from either soluble Co(II) or Co(III) species.