Portugaliae
Electrochimica Acta

As Cr (VI) compounds used to formulate conversion layers provide enhanced anticorrosive protection to zinc coatings, but they are produced using hazardous chemicals, the development of “green” technologies is a paramount purpose. Consequently, the corrosion behavior of zinc coatings subjected to a Cr3+ based passivating treatment, with and without sealing, was studied through EIS measurements in 0.5 M Na2SO4 solution. The analyses of the experimental data allowed inferring that the Cr3+-based conversion treatment with an adequate sealer provides good corrosion resistance and, coupled to an adequate painting system, could be a suitable alternative to traditional chromate coatings.

The inhibition performance of two Schiff bases, namely (A) Benzenamine, 2-chloro-N-[(4-methoxyphenyl)methylene] and (B) Benzenamine, 3-chloro-N-[(4-methoxyphenyl)methy-lene] as corrosion inhibitors for Al-Pure in 1.0 M HCl has been investigated by galvanostatic polarization measurement, electrochemical impedance spectroscopy (EIS) and weight loss method. Galvanostatic polarization study showed that two inhibitors are mixed type with predominant action on the cathode. The adsorption of inhibitors on Al-Pure surface was found to follow Langmuir adsorption isotherm and the thermodynamic parameters (Ea, ΔGads and Qads) were determined. Two Schiff bases have shown remarkable inhibition on the corrosion of Al-Pure in 1.0 M HCl solution. The high inhibition efficiency was attributed to the blocking of active sites by adsorption of inhibitor molecules on the metal surface.

Membrane selective electrodes were used to determine Naftidrofuryl Oxalate (NFL) in presence of its alkaline degradate (I). The membrane selective electrodes include construction of water insoluble ion-association complexes. These are NFL-tetraphenyl borate (NFL-TPB), NFL- reinikate (NFL-R). These complexes are used as electroactive materials, in poly-vinyl chloride (PVC) matrix membrane sensors, for the determination of NFL. The performance characteristics of these sensors, evaluated according to IUPAC recommendations, reveal fast, stable and linear response for NFL. The sensors are used for determination of NFL in plasma. The suggested method was used to determine NFL in synthetic mixtures and in commercial tablets. The obtained results were statistically compared with official HPLC method, showing no significant difference with respect to accuracy and precision.

Aqueous extracts of the leaves of Anthocleista djalonesis (AD) have been investigated as non toxic corrosion inhibitors for mild steel in acidic environments (1 M HCl and 0.5 M H2SO4, respectively). Corrosion rates were evaluated at 30 oC using the weight loss, electrochemical impedance spectroscopy and potentiodynamic polarization techniques. AD extract was found to inhibit mild steel corrosion in both acidic media via adsorption of the extract organic matter on the metal/solution interface. Polarization data indicate that the extract functioned via a mixed inhibition mechanism, affecting both the cathodic and anodic partial reactions of the corrosion process. Molecular dynamics (MD) simulations were performed to illustrate the adsorption process of some specific components of the extract.

The present study investigates the significance of different coating process parameters on the corrosion behaviour of electrolessly deposited Ni-P-W coatings on mild steel substrate. The process parameters considered are concentration of nickel source, concentration of reducing agent, concentration of tungsten source and annealing temperature. The corrosion characteristic is evaluated by electrochemical impedance spectroscopy technique. The responses considered are charge transfer resistance and double layer capacitance. The Taguchi technique coupled with grey analysis is employed to find out the optimum combination of the process parameters for better corrosion resistance. Analysis of variance (ANOVA) reveals the contribution of the process parameters on the corrosion property of Ni-P-W coating. Finally a validation test is performed to justify the experimental result. The microstructure of the surface is studied by scanning electron microscopy (SEM); energy dispersive x-ray analysis (EDX) reveals the chemical composition and the x-ray diffraction analysis (XRD) is used to identify the phase transformation behaviour of the coating.

The electrochemical treatment of leachate samples from a Portuguese intermunicipal sanitary landfill was carried out using combined electrocoagulation/anodic oxidation processes. The electrocoagulation (EC) was performed with iron consumable anodes, at different initial pH, with and without stirring, at different applied potentials. In the anodic oxidation (AO) assays, a boron-doped diamond anode was used and applied current densities of 10 to 30 mA/cm2 were tested. The influence of the experimental conditions of the electrocoagulation pretreatment on the anodic oxidation performance was also assessed. In the EC assays the lowest iron and energy consumptions per mass of organic load removed were obtained at initial pH of 4 in the unstirred assays. In the combined treatments, the highest average current efficiency in the anodic oxidation was obtained for the samples with EC pretreatment performed at pH of 6. For the combined treatment with EC pretreatment run at natural pH of 8.6, an increase in AO current density led to a decrease in average current efficiency.