Portugaliae
Electrochimica Acta

The electrokinetic technique is used to remediate hydrocarbon-contaminated soil. The aim of this paper is to evaluate the feasibility of using this technology to remediate oil- contaminated soils in the Gulf of San Jorge. The soils used in this experiment were unsaturated soils contaminated by oil field operations being carried out in the area and previously remediated by landfarming. A potential difference of 0.5V cm-1 was applied to the electroremediation cells for 120 days; bridges of phosphate salt were used for the cells. Total hydrocarbons decreased from 4.22% to 3%, modifying the percentages of aliphatic, aromatic and polar hydrocarbons. The pH changed from 7.96 to 8.6 and 7.1 in the cathode and anode, respectively. The final pH values were compatible with the degrading bacterial community, whose colony-forming numbers did not present any alteration. On the cathode, there was an increase in the percentage of Gram-positive bacteria. Most of the species isolated were identified as Microbacterium luteus.

In an attempt to improve the corrosion inhibition potential of Anogessius leocarpus gum exudates for mild steel in solutions of HCl, corrosion inhibition efficiencies of the gum, KI, KCl, and KBr were determined experimentally using weight loss and gasometric methods. 0.05 M KI, 0.05 M KBr and 0.05 M KCl were combined with various concentrations of Anogessius leocarpus gum and their combined inhibition efficiencies were used in computing synergistic parameters for the respective combinations. The results obtained indicated that combination of 0.4 and 0.5 g/L of AL gum with 0.05 M solutions of KI and KBr, respectively, enhanced inhibition efficiency of the gum. However, for all concentrations of AL gum, combinations with 0.05 M KCl recorded a remarkable increase in inhibition efficiency, but calculated values of the synergistic parameter indicated that the adsorption of AL gum on mild steel surface is antagonized by the presence of Cl- . Theory of competitive and co-operative adsorption has been used to explain the co-adsorption of the gum and the halides. From calculated values of activation energy (< 80kJ/mol), free energy of adsorption (< -40 kJ/mol) and the variation of inhibition efficiency with temperature, the adsorption characteristics of the gum, halides and that of gum-halide mixtures were found to be consistent with the mechanism of physical adsorption. The adsorption was also found to be endothermic, spontaneous and favored the Langmuir adsorption model.

The inhibition of steel corrosion in hydrochloric acid and sodium chloride solutions by Nicotiana leaves extract was investigated by potentiodynamic polarization and electrochemical impedance spectroscopy measurements. Polarization curves showed that the extract behaves as a mixed type inhibitor in acidic medium, while it acts as anodic type in neutral medium. Impedance measurements indicated that the size of the semicircles obtained increased with increasing the concentration of the extract and decreasing the chloride ion concentration. Nicotiana leaves extract was found to be more effective in controlling corrosion of steel in acidic solution than in neutral one. The activation parameters of the corrosion reaction of steel in acid media in absence and presence of nicotiana leaves extract were also calculated and discussed.

Synthesis of new Ag+ ion conducting glass-polymer electrolytes (GPEs): (1-x) PEO: x [0.75(0.75AgI:0.25AgCl):0.25(Ag2O:P2O5)], where 0 < x < 50 wt. (%), are reported. GPEs have been casted using hot-press techniques. The highest conducting composition 70PEO: 30[0.75(0.75AgI:0.25AgCl):0.25(Ag2O:P2O5)], with conductivity (σ) ~ 6.0 × 10-6 S.cm-1, was identified from the compositional dependent conductivity studies and this has been referred to as the Optimum Conducting Composition (OCC). Approximately three orders of conductivity enhancement have been achieved in GPE OCC from that of the pure polymer PEO. The glass-polymer complexation has been confirmed by SEM and DSC analysis. Ion transport parameters viz. ionic conductivity (σ), ionic mobility (μ), mobile ion concentration (n) and ionic transference number (t(ion)) have been characterized using different experimental techniques. Solid-state polymeric batteries were fabricated using GPE OCC as electrolyte and the cell-potential discharge characteristics were studied under different load conditions at room temperature.

The inhibitive action of the Argan press cake extract (ACE) against corrosion of C38 steel in a 1 M HCl solution was investigated using potentiodynamic polarization curves, electrochemical impedance spectroscopy (EIS) and weight loss measurements. The inhibition efficiency increases with increasing extract concentration and decreases with temperature. The kinetic parameters (activation energy, pre-exponential factor, enthalpy of activation and entropy of activation) were calculated and discussed. The Argan press cake extract acted as a mixed-type inhibitor with predominant cathodic effectiveness. The Nyquist plots showed that on increasing ACE concentration, increases charge transfer resistance and decreases double layer capacitance. The adsorption of components of the the Argan press cake extract (ACE) on the surface of the C38 steel follows the Langmuir adsorption isotherm. E (%) values obtained from various methods used are in good agreement.

The electrochemical treatment of leachate samples collected in a Portuguese intermunicipal sanitary landfill was carried out using combined electrocoagulation followed by anodic oxidation processes. Samples were collected after the biological treatment of the in situ plant and in permeate of an ultrafiltration operation, located after the biological treatment. Electrocoagulation was performed with iron consumable anodes, at different initial pH, with and without stirring, at different applied potentials. In the anodic oxidation assays a boron-doped diamond anode was used and applied current densities from 100 to 300 A m-2 were tested. The influence of the experimental conditions of the electrocoagulation pretreatment on the anodic oxidation performance was also assessed. In the electrocoagulation assays the lowest iron and energy consumptions per mass of organic load removed were obtained at initial pH of 4 for the samples collected after the biological treatment and at initial pH of 6 for the sample collected in the ultrafiltration permeate, all in the unstirred assays. In the anodic oxidation, the highest average current efficiencies were obtained in the assays run at lower current density, being higher for the samples collected after the biological treatment. For both type of samples, the correction of the pH prior to the electrocoagulation pretreatment led to a decrease in the average current efficiency during the anodic oxidation.

potentiometric measurement was proposed using the mediator hexacyanoferrate. In this methodology, EMF of the cell exclusively depends on glucose concentration and independent on reference half-cell electrode potential or mediator concentration or any other interfering factors. Electrochemical as well as mathematical models were proposed. Numerical computations along with boundary conditions were evaluated for the proposed models, to reduce the deviation in the interpolated results. Molar ratio of mediator to glucose was correlated with EMF cell. Numerical simulations, Legendre polynomials and Lagrange coefficients iterations can be executed through computer programs.

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.

Synthesis, characterization and polymeric battery studies of Na+ ion conducting Nano- Composite Polymer Electrolyte (NCPE) membranes: (1-x) [75PEO: 25NaPO3]: x SiO2, where x = 0 - 15 wt. (%), has been reported. NCPE membranes have been casted using a novel hot-press technique in place of the traditional solution cast method. The dispersal of SiO2 in SPE host: (75PEO: 25NaPO3), a conductivity enhancement of an order of magnitude achieved in NCPE film: [93 (75PEO: 25NaPO3): 7 SiO2]. This has been referred to as Optimum Conducting Composition (OCC). Material characterizations have been done with the help of XRD, SEM and DSC techniques. The ion transport behaviour in hot-pressed NCPEs has been discussed on the basis of experimental measurements on some basic ionic parameters viz. conductivity (σ), ionic mobility (μ), mobile ion concentration (n) and ionic transference number (tion). The temperature dependent conductivity studies have been done to compute the activation energy (Ea) values from the ‘log σ – 1/T’ Arrhenius plots. The ion conducting solid state polymeric battery was fabricated and cell-potential discharge characteristics have been studied at different load conditions.

The influence of benzothiazole derivatives on corrosion inhibition of mild steel in 1 M H2SO4 was studied by weight loss, potentiodynamic polarization and AC-impedance techniques. The synergistic effect by the addition of halide ions had been studied. The experimental results showed that the inhibition efficiency increases with increasing inhibitor concentration, but decreases with increasing temperature; potentiodynamic polarization curves showed that benzothiazole derivatives acted as cathodic inhibitors in 1 M H2SO4. This was supported by the impedance measurements which showed a change in the charge transfer resistance and double layer capacitance, indicating adsorption of Benzothiazole derivatives on the mild steel surface. Atomic absorption spectroscopy studies showed that the inhibition efficiency increases with increasing inhibitor concentration.

Pollution control measures have resulted in replacement of chlorine by peroxide as bleaching chemical. Change of chemical affects corrosion aspects, the suitability of existing plant metallurgy and materials of construction of bleach plants. Accordingly long term immersion and electrochemical corrosion tests were conducted on stainless steel 304L, 316L, 2205 and 6% Mo and mild steel in peroxide solutions of pH 10. The materials were tested for uniform corrosion, pitting and crevice corrosion and attack around the weld area. Corrosion attack estimated from long term immersion tests is found in agreement, by and large, with that analyzed from electrochemical test. E-pH diagrams drawn for water-peroxide system have been used to understand the corrosivity of the peroxide media. An attempt has been made to suggest a suitable material of construction for handling the test media on the basis of degree of corrosion attack on them and their cost and the mechanical properties.

Spontaneous deposition of tin (Sn) in polycrystalline platinum (Pt pc) from a sulfuric acid solution of tin salts, was evaluated by conventional electrochemical techniques, to determine its characteristics. Tin was deposited from a solution of SnCl2 or SnSO4 in sulfuric acid 1 M. The degree of surface coating by Sn was calculated by evaluating the region of hydrogen electrosorption through voltammograms performed using solutions containing only the supporting electrolyte, and the supporting electrolyte containing the Sn salt, respectively. The adsorption behavior of tin and oxidation have been studied by the results obtained with platinum electrodes and electrodes of platinum/tin, considering as comparative parameter the adsorption efficiency with respect to the area free of platinum.

The degradation of crystal violet (CV) and malachite green (MG) by potassium persulfate, was investigated by spectrophotometric methods. The behavior of degradation of crystal violet by persulfate was found to be similar to that of malachite green with only one important difference concerning the order with respect to the dye: the degradation is pseudo second order with respect to CV, but first order with respect to MG. The order with respect to persulfate is one in both cases. Degradation of CV by persulfate was effective at pH range of 2-8 and was found to increase with an increase in the initial concentrations of persulfate, temperature, and the presence of Ag+. The factors that were found to decrease the degradation rate of CV include: the initial concentration of CV, and the presence of halide salts and of the surfactant SDS. The rate of degradation remained the same after addition of Co(II), Ni(II) and Cu(II) salts. The activation parameters of the degradation reaction (Ea, ΔG#, ΔH# and ΔS#) were calculated. Finally, cytotoxic study revealed a decrease in the toxicity of the degradation products.

Silver nanoparticles (AgNP) were synthesized by electrochemical method using high purity metallic silver in the presence of the surfactant Pluronic® f127. The synthesized nanoparticles were characterized using UV-Vis spectroscopy, Dynamic Light Scattering (DLS), X-Ray Dispersion Spectroscopy (XDS) and Scanning Electron Microscopy (SEM). The antimicrobial activity of AgNP was evaluated against Escherichia Coli. In presence of surfactant, the prepared nanoparticles led to a monomodal distribution with an average size less than 100 nm. The minimal inhibitory concentration (MIC) of the resulting suspension was evaluated using micro dilution method and the MIC results are satisfactory.

The effect of various surfactants on the volume% codeposition of SiC in a nickel matrix was evaluated. Of the various surfactants tried, tetra methyl ammonium hydroxide (TMAH) was found to be the best for improving the quality of the deposits as well as the homogenous distribution of particles and with reasonable volume% of silicon carbide incorporation in the matrix. Composites were produced using 1 μm and 50 nanometer size powders. The effect of silicon carbide concentration and bath operating variables on the volume% of SiC incorporation in the deposit and the deposition rates were estimated. Substantial improvement in mechanical properties such as hardness and wear resistance was obtained with the nano SiC composite compared to the micro SiC composite.