J.R. Vilche

Oxygen evolution on electrodeposited cobalt oxides

This paper concerns the preparation of cobalt oxides through anodic deposition from Co(NO3)2 aqueous solutions on different substrates. The electroformed oxide films exhibit good chemical stability and lower oxygen overvoltages, irrespective of the substrate material. Electrocatalytic properties are investigated through polarisation curves and impedance measurements, while the active surface area is estimated by cyclic voltammetry. Experimental data are analysed in terms of a possible reaction mechanism.

Application of EIS and SEM to evaluate the influence of pigment shape and content in ZRP formulations on the corrosion prevention of naval steel

Abstract The effects of pigment volume concentration and morphology of zinc particles employed in the formulation of zinc rich paints (ZRP) suitable for the corrosion protection of naval steel in sea water, have been investigated using electrochemical impedance spectroscopy combined with open circuit potential measurements and SEM micrograph analysis. Different ZRP samples were tested during exposure to artificial sea water for up to 70 days. The characteristics and properties of the naval steel/ZRP coating/sea water systems were determined from an impedance transfer function model which involves the reactions occurring at the metal/ZRP and ZRP/solution interfaces as well as diffusion processes through the active ZRP coating. Information concerning the influence of concentration and shape of the zinc pigment on the corrosion protective behaviour of ZRP coatings and on the exposure time dependence of the system parameters allowed to interprete the form in which the galvanic action and the barrier effect diminish progressively. The degree of rusting of the steel substrates as well as the blistering resistance of the formulated ZRP have been also evaluated according to conventional ASTM standards.

Comparative study of organic inhibitors of coppercorrosion

Abstract The corrosion behaviour of copper in the presence of two organic inhibitors that belongto the oxime group (salycilaldoxime (SO) and benzoinoxime (BO)) has been investigated inneutral aqueous NaCl solutions. Weight-loss measurements and electrochemical impedancespectroscopy (EIS) were applied to analyse the effect of the organic compounds on the corrosioninhibition of copper. Morphology of the copper substrate after corrosion in the presence andabsence of the inhibitors was examined using scanning electron microscopy (SEM). Fouriertransform infrared (FTIR) and X-ray photoelectron (XPS) spectroscopies were used tocharacterise the surface film. A polymeric Cu (II)-inhibitor complex that totally covered thecopper surface was identified, exhibiting strong corrosion inhibition. In the first stage, copperoxides are formed adhering to the metallic surface. The inhibitory mechanism on the Cudissolution process was related to both the chelating effect of Cu (II)ions close to the coppersurface, which avoids the action of aggressive Cl− or OH− ions in solution, and the blockingaction of the organic complex surface film.

A survey of Argentinean atmospheric corrosion: I—Aluminium and zinc samples

The atmospheric corrosion of aluminium and zinc samples exposed at six test sites with known ambient parameters in Argentina was investigated after different outdoor exposition periods. Corrosion damage was determined by weight-loss measurements. Both D.C. and A.C. electrochemical techniques, performed in 0.1 M Na2SO4 solution employing the exposed face of the test samples, were used to characterize the protectivenesses of the surface layers generated on the metals at different exposure times during the atmospheric corrosion process in the distinct environments. The time dependence of corrosion rates as compared with the weight-loss data as well as with information from SEM and EDAX observations of the rusts concerning the structure and morphology of surface corrosion products and the presence of pollutants.

The corrosion protection of steel in sea water using zinc-rich alkyd paints. An assessment of the pigment-content effect by EIS

Abstract The effect of pigment volume concentration ( c v,p ) on the corrosion resistance properties of zinc-rich paints (ZRP) has been investigated using electrochemical impedance spectroscopy (EIS) combined with cathodic protective potential measurements. Painted naval steel samples were studied during the exposure to artificial sea water for up to 45 days. ZRP coatings were prepared employing zinc pigment content in the 77–88% concentration range. Results show clearly that samples prepared with c v,p values >86% deteriorated more rapidly than panels painted using a relatively lower pigment content. The corrosion behaviour of painted steel samples was found to be practically independent of c v,p within the 78–86% range. The cathodic protection effect in action during 45 days immersion time arises because these alkyd resin paint coatings behave like a porous active surface layer. Under aggressive conditions similar to those afforded by the artificial sea water, zinc-rich alkyd coatings containing c v,p values within the 78–86% range seem to provide longer corrosion protection to steel substrates than other types of ZRP commonly used.

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...

The characteristics of the potentiodynamic potential/current profiles obtained with the Ni/0.5N H2SO4 interface. A contribution to the mechanism of the electrode process

Abstract Electrochemical data derived from different simple and complex potentiodynamic techniques for the Ni/0.5 N H 2 SO 4 interface furnish a new insight about the activation and initial stage passivation of nickel. The anodic dissolution of nickel involves a metal surface which is either partially or completely covered by species such as NiOH, [NiOH.Ni(OH) 2 ] or [Ni(OH) 2 .NiOOH]. The chemical dissolution of the various species in the acid electrolyte occurs at different rates. The relative dissolution rates can be estimated from the data derived from the complex triangular potential perturbations. The change of the E / I profile during cycling is explained through a complex reaction sequence which is in agreement with recently postulated reaction schemes and reported optical data.

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.

The application of electrochemical impedance spectroscopy and identification procedures to the investigation of the dissolution and passivation of iron in carbonate—bicarbonate buffers at 25°C

An electrochemical impedance spectroscopy study of the dissolution and passivation of polycrystalline iron is carbonate—bicarbonate buffers at 25°C is reported. The impedance spectra analysis was performed by using an identification procedure to estimate initially the dynamic parameters from the measured impedance obtained by employing both sinusoidal and pseudo-random binary sequence perturbation, followed by a quantitative fitting on the basis of reaction schemes in terms of formal rate constants. Impedance spectra and steady-state polarization characteristics are accounted for by a reaction model involving the parallel formation of Fe(OH)2 and soluble Fe(II) species. The concentration of bicarbonate ions determines the overall current in the prepassive potential range.

An electrochemical impedance study on the kinetics and mechanism of the hydrogen evolution reaction on nickel molybdenite electrodes

Abstract Electrodeposited Ni NiMoS 2 electrodes have shown good electrocatalytic activity towards the hydrogen evolution reaction as well satisfactory long-term operational performance. The hydrogen evolution reaction on these electrodes, which in previous investigations using steady-state polarizations, cyclic voltammetry and scanning electron microscopy revealed high surface area and a very heterogeneous surface morphology, has been studied by applying electrochemical impedance spectroscopy (EIS). The kinetics and mechanism of the hydrogen evolution reaction (HER) on electrodeposited Ni NiMoS 2 electrodes have been investigated in the frequency range 5 mHz ⩽ f ⩽ 10 kHz. A detailed dynamic system analysis is presented taking into account the contributions of Tafel-Volmer-Heyrovsky reaction steps as well as the absorption and diffusion of hydrogen atoms into the electrode material. For comparison results obtained for the HER on electrodeposited Ni electrodes are also discussed.