Portugaliae
Electrochimica Acta

The corrosion behaviour of welded maraging steel in hydrochloric acid solutions was studied over a range of acid concentration and solution temperature by electrochemical techniques like Tafel extrapolation method and electrochemical impedance spectroscopy. The corrosion rate of welded maraging steel increases with the increase in temperature and concentration of hydrochloric acid in the medium. The energies of activation, enthalpy of activation and entropy of activation for the corrosion process were calculated. The surface morphology of the corroded sample was evaluated by surface examination using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS).

An investigation about the corrosion resistance of SS316L alloys in artificial blood plasma environments in presence and absence of amoxicillin has been carried out by using electrochemical techniques. Tested alloys included 18% Cr, 12% Ni, 2.5% Mo, <0.03 C, balance iron, using artificial blood plasma solution. Electrochemical techniques included potentiodynamic polarization curves, linear polarization resistance and AC impedance spectroscopy. Different techniques have shown that generally speaking, SS316L alloys show a more corrosion resistance in artificial blood plasma in the presence of 100 ppm amoxicillin than in the presence of 50 ppm of amoxicillin and in the absence of amoxicillin. Their corrosion resistance is increased as the quantity of amoxicillin is increased in artificial blood plasma.

Aluminium is the most widely used non ferrous metal. It is very needful to prevent this metal from corrosion .Corrosion inhibitors are one of the widely used methods to control corrosion. The purpose of this paper is to make people aware of organic corrosion inhibitors. Organic inhibitors are mainly present in natural products. It has been found that plant extracts and natural products show inhibition efficiency up to 98%. They are also non –toxic, eco- friendly, very cheaper. In the present work, natural products are used at various conditions and their inhibition efficiency is calculated by different methods; they obey various adsorption isotherms; the protective films formed by the inhibitors are analyzed by techniques such as electrochemical methods, FTIR, HPLC-RP, SEM, EDS.

A modified electrode is fabricated by the electrodeposition of polyaniline-polystyrene sulphonate composite onto the carboxylated graphene modified graphite electrode for the detection of hydrogen peroxide (H2O2). The modified electrode displayed excellent catalytic response to the reduction of hydrogen peroxide in neutral pH. It was found that the presence of carboxylated graphene in the sensor system could effectively increase the electron transfer rate and stability. The modified electrode was characterized by cyclic voltammetry, electrochemical impedance spectroscopy and atomic force microscopy. Chronoamperometric studies showed the linear relationship between the reduction peak current and the concentration of H2O2 in the range 25 to 350 μM (R = -0.995) with the detection limit of 1×10-6 mol/L (S/N=3). Further, electrochemical analysis of H2O2 in the presence of common interferents such as dopamine, uric acid and ascorbic acid with the modified electrode reveals that there is no overlapping signal from the interferents.

Chlorophenols are a group of special interest due to their high toxicity and low bio degradability. Advanced oxidation process constitutes a promising technology for the treatment of wastewaters containing non-easily removable organic compounds. Several electro chemical processes are based on mediated electro chemical oxidation. The present study envisages the utility of electro-fenton and photo-fenton process for the degradation of parachlorophenol from aqueous solution by the electro oxidation under acidic condition. Experiments were carried out under batch recirculation conditions with stainless steel as cathodes and RuO2 coated titanium expanded mesh as anodes. Electrolysis was carried out with various current densities and flow rate using mediated electro chemical oxidation process with fenton mediator (Fe2+ / Fe3+ + H2O2). Extent of dehydration and reduction in COD was studied as a function of applied current, electrolysis time and concentration of ferrous ion. The electrolysis was carried at optimised conditions to achieve efficiencies higher than 80%.

The inhibition efficiency (IE) of metronidazole (MZ)-Zn(II) system in controlling corrosion of mild steel in aqueous solution containing 60 ppm of Cl- ion has been evaluated by weight loss method. Weight loss study reveals that the formulation consisting of 140 ppm of MZ and 50 ppm of Zn(II) has 84% inhibition efficiency in controlling corrosion of mild steel immersed in aqueous solution containing 60 ppm of Cl- ion. Polarization study reveals that this system as a mixed type of inhibitor controlling the cathodic and anodic reaction to an equal extent. AC impedance reveals that a protective film is formed on the metal surface. The FTIR spectra revealed that the protective film consists of Fe(II)- MZ complex.

The corrosion inhibitive effects of 2-(4-methylphenyl)-1,4-dihydroquinoxaline (Q1) on carbon steel surface in hydrochloric acid solution was studied using weight loss measurements, electrochemical impedance spectroscopy (EIS), Tafel polarization techniques and quantum chemical approach, using the density functional theory (DFT). Inhibition efficiency increased with increase in concentration of the inhibitor. The degree of surface coverage of the adsorbed inhibitor was determined by weight loss technique, and it was found that the results obeyed Langmuir adsorption isotherm. Tafel polarization data indicated that this inhibitor is of mixed type. EIS shows that charge-transfer resistance increases and the capacitance of double layer decreases with the inhibitor concentration, confirming the adsorption process mechanism. Trends in the calculated molecular properties (e.g., dipole moment, HOMO and LUMO energies) were compared with trends in the experimentally determined inhibition efficiency. The results show that trends in the quantum chemical descriptors are in agreement with the experimentally determined inhibition efficiencies.

The influence of water-soluble alginates (Alg) and pectates (Pect) anionic polyelectrolytes as natural polymers containing secondary alcoholic groups on the rate of dissolution of aluminum metal in alkaline medium has been investigated by gasometric and weight-loss techniques. The results showed that addition of alginates or pectates to the tested solutions leads to a remarkable decrease in the corrosion rate of Al in NaOH. The magnitude of inhibition efficiency was found to be larger in case of pectates. Factors affecting the corrosion process such as the concentration of the inhibitor and the corrosion medium, structure of the inhibitor and temperature have been examined. The kinetic parameters of corrosion have been evaluated and a suitable mechanism for the inhibition is discussed.

The effect of 2-amino-4,6-dihydroxy pyrimidine (ADHP) on the corrosion of carbon steel in 1 M HCl has been studied using weight loss and galvanostatic polarization measurements. The percentage inhibition efficiency was found to increase with increasing concentration of the inhibitor, and with decreasing temperature. The inhibitive effect of these compounds was explained on the basis of the formation of an insoluble complex adsorbed on the metal surface. The adsorption process follows Langmuir adsorption isotherm. The effect of temperature on the rate of the corrosion in the absence and presence of these compounds was also, studied. The activated thermodynamic parameters were calculated and explained.

The inhibition efficiency (IE) of Amino Trimethylene phosphonic acid (ATMP) in controlling corrosion of carbon steel immersed in ground water in the absence and presence of Zn2+ has been evaluated by weight loss method. It is observed that the synergistic formulation consisting of 250 ppm ATMP and 10 ppm of Zn2+ has 98% IE. Polarization study reveals that ATMP-Zn2+ system functions as a cathodic inhibitor system. AC impedance study reveals that a protective film is formed on the metal surface.

The inhibitive effect of Treculia Africana leaves extract (TALE) in the corrosion of aluminium in HCl solution was studied using weight loss and thermometric methods at 30 - 60 ºC. The results showed that TALE acted as a corrosion inhibitor of aluminium in HCl. Inhibition efficiency increased with increase in TALE concentration, but decreased with increase in temperature. TALE interaction with the metal surface was found to obey Freundlich and El-Awady adsorption isotherms. The obtained heats of adsorption values were negative. A phenomenon of physical adsorption is proposed for the adsorption behavior of TALE.

Cyclic voltammetry was used in cetyltrimethylammonium bromide (CTAB) micellar solution to determine the half-wave potentials of selected chlorophenols, CPs. It is observed that all the electrochemical parameters of the studied CPs decrease with an increase in the number of chlorine atom(s) attached to the parent compound. The mathematical relationship between the obtained E1/2 and the number of chlorine atoms in the parent compound is given. The formal potentials, E0', of the CPs are approximated from the obtained half-wave potentials.

Four torsemide-selective electrodes all on solid state graphite support were developed and characterized in polyvinylchloride matrices. Precipitation-based technique with tetraphenylborate (TPB) as an electroactive material in polyvinylchloride (PVC) matrix was used for sensor 1 fabrication without incorporation of an ionophore. 2-hydroxypropyl-β-cyclodextrin (HP-β-CD) based technique with tetraphenylborate and either dioctyl phatalate (DOP), dibutyl sebasate (DBS) or 2-nitrophenyl octyl ether (o-NPOE) as plastisizer in carboxylated polyvinylchloride (PVC- COOH) matrix were used for sensor 2, 3 and 4 fabrications, respectively. Fast and stable Nernstian responses were evaluated according to IUPAC recommendations in the concentration ranges from 1x10-5 to 1 x 10-3 M for sensor 1 , from 1x10-5 to 1x 10-2 M for sensor 2, from 1x10-6 to 1 x 10-4 M for sensor 3, and from 1x10-6 to 1 x 10-3 M for sensor 4 . The sensors show good selectivity to the drug in presence of a variety of inorganic and organic interferents including acid degradation product of torsemide, related substances and pharmaceutical excipients. Validation of the method showed the suitability of the proposed electrodes for the use in the quality control assessment of the drug. Furthermore, statistical comparison between the results obtained by the proposed method and the official method of the drug was performed and no significant difference was found.

Kinetic study of the indirect oxidation of methylene blue on Pt electrode in presence of several strong electrolytes is undertaken. Different operating conditions that affected the treatment process were studied in order to find the best conditions. The order with respect to methylene blue is zero order in presence of chloride, but it is second order in presence of bromide. The oxidation rate was affected by current density, halide concentration (KCl, KBr), nature of supporting electrolyte and initial pH. However, the initial dye concentration and temperature did not show a significant effect. The oxidation of methylene blue in presence of iodide, fluoride and sulfate is absent, but it is important in presence of chloride and bromide. The product of the indirect oxidation is the chloronated (bromonated) methylene violet bernthsen.

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.