Portugaliae
Electrochimica Acta

The corrosion behavior of mild steel in dimethyl sulfoxide containing various concentrations, i.e., 0.001, 0.005, 0.010, 0.015 and 0.020 M of hydrochloric acid has been studied in presence of 0.1 M tetra ethyl ammonium chloride as supporting electrolyte by applying electrochemical techniques. The results of these experiments have been supplemented by surface analysis of the samples exposed to corrosive solution under different experimental conditions. The electrochemical investigation was done potentiostatically by varying the concentration of HCl in DMSO and the experimental temperature as well.

The corrosion inhibition effect of acid extract of the pericarp of the fruit Garcinia mangostana on mild steel in hydrochloric acid medium is studied. Using weight-loss data, corrosion rate (CR) and thermodynamic parameters such as energy of activation for corrosion of mild steel (E), heat of adsorption of the inhibitors on the metal surface (Q) and change in free energy (∆G) are calculated. Adsorption isotherm is also recorded between log C and θ. Electrochemical parameters are evaluated from AC impedance and Tafel polarization studies in the presence and absence of different concentrations of inhibitor. Infra-red spectra are recorded for the extract and the adsorption product to find out the changes in the functional group frequencies of the organic components of the extract. The surface morphological changes are analysed using the SEM images. The entire study shows that the pericarp extract of the fruit G. mangostana is a non-toxic, cost-effective corrosion inhibitor for mild steel in acid medium.

The corrosion inhibition of stainless steel in 0.9% NaCl solution in presence of poly(vinyl alcohol) (PVA) is discussed according to electrochemical measurements, such as potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).The morphology of the surface was analyzed using Scanning Electron Microscopy (SEM). The composition of the layer formed on stainless steel surface was estimated using X-ray Photoelectron Spectroscopy (XPS) technique. Electrochemical measurements indicated that the presence of PVA in NaCl solution decreases the corrosion current and increases the polarization resistance. The values of inhibition efficiency obtained from polarization curves and EIS measurements are in good agreement. In absence and in presence of PVA, SEM images showed that the stainless steel surface was covered with a non-uniform layer and a uniform adsorbed film, respectively. XPS analysis indicated that the surface layer consists of PVA containing a small amount of other elements, such as Na and Cl.

The electrochemical oxidation of toluene in aqueous-acid medium was studied on monolithic and reticulated glassy carbon electrodes using cyclic voltammetry. The oxidation potential was 1.7 V for both electrodes. However, the normalized oxidation currents were higher on reticulated glassy carbon, showing more catalytic activity than on the monolithic glassy carbon. To normalize the obtained anodic current values, a method for the determination of the electrodes effective area was used, which consists in the underpotential deposition of a copper monolayer.

The beneficial effects of the ultrasound (US) like the cleaning of electrode surface and enhancement of mass transport were evaluated in association with potentiostatic electrolyses for the degradation of pentachlorophenol (PCP) at 3.0 V vs. Ag/AgCl, using a boron-doped diamond (BDD) electrode during 270 minutes. Different decay levels of the PCP spectrum bands in 220, 251 and 321 nm, respectively, were observed after application of ultrasound without electrochemical process (18.1, 17.7 and 19.8 %), silent electrolyses (29.3, 71.6 and 70.8 %), pulsed sonoelectrolysis (31.0, 75.1 and 76.3%) and sonoelectrolyses (39.2, 80.0 and 82.6 %). For silent and sonoelectrolyses processes, cleaning/reactivation of the BDD surface by acetonitrile and/or electrochemical treatment was necessary. The pulsed sonolectrolysis were carried out purposely without cleaning/reactivation of the surface. The results showed greater PCP degradation for insonated studies than those obtained for the silent electrolyses, due to the increase of mass transport, minimization of the electrode fouling and the combined generation of hydroxyl radicals by both ultrasound and the polarized BDD surface. These tools (US and BDD), especially the pulsed sonoelectrolysis, can improve the degradation of pesticides and their metabolites in the environment and enable the use of sonoelectrochemistry for wastewater remediation.

The electrochemical oxidation of cibacron red FN-R (CB) has been studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) at a glassy carbon electrode (GCE) in phosphate buffer solutions of pH (2.54–11.79) used as supporting electrolytes. The voltammetric behaviour showed that the electro-oxidation process gave rise to a single peak at 0.692 V vs. Ag-AgCl using DPV in phosphate buffer solution at (pH 3.34). The oxidation process was shown to be irreversible and adsorption-controlled. An analytical method was developed for the determination of cibacron red FN-R in phosphate buffer solution at (pH 3.34) as supporting electrolyte. The anodic peak current varied linearly with cibacron red FN-R concentration in the range 2.0x10−6 mol/L to 1.0x10−5 mol/L of cibacron red FN-R with a limit of detection (LOD) of 4.49x10−7 mol/L and limit of quantification (LOQ) of 1.49x10-6 mol/L. Validation parameters, such as accuracy, precision and recovery were evaluated. The proposed method was successfully applied to the determination of cibacron red FN-R in synthetic industrial effluents and the analytical results compared well with those obtained by the spectrophotometric method.