Portugaliae
Electrochimica Acta

Gas chromatography mass spectrophotometer (GCMS) analysis of Ficus tricopoda gum indicated the presence of 4.75, 56.15, 32.10 and 7.00 % of camphene, sucrose, 2-methylene cholestan-3-ol and 7-hexadecenal, respectively. Several stretching and bending vibrations were observed in the Fourier transformed infra-red (FTIR) spectrum of the gum. Physicochemical examinations of the gum revealed that it is pale yellow in colour, mildly acidic, ionic and display characteristics of sour taste. The solubility of the gum in water was found to increase with increase in temperature. Knowledge of the chemical constitution of the gum (hence chemical structures of its constituents) was useful in predicting the corrosion inhibition potential of Ficus tricopoda (FT) gum. Consequently, the gum was found to be a good adsorption inhibitor for the corrosion of aluminum in solution of H2SO4. The adsorption of the gum (which, followed first order kinetic) was found to be endothermic at FT gum critical concentration of 0.3 g/L and exothermic at concentrations above the critical limit. The short coming of the Langmuir adsorption model in describing the existent of interaction between the molecules of the gum was complimented by the Frumkin and Dubinin-Radushkevich adsorption models. Calculated values of activation and free energies of activation indicated that the adsorption of Ficus tricopoda gum on Al surface exhibited both physical and chemical adsorption mechanism.

The inhibition efficiency [IE] of an aqueous extract of eclipta alba leaves in controlling corrosion of carbon steel in sea water [Thondi, Tamil Nadu, India] has been evaluated by weight loss method. The weight loss study reveals that the formulation consisting of 6 mL of EAE (Eclipta Alba extract ) and 25 ppm of Zn2+ has 92% inhibition efficiency in controlling corrosion of carbon steel in sea water. Polarization study reveals that EAE and Zn2+ system functions as a mixed type inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. The nature of the metal surface has been analysed by FTIR spectra and AFM analysis.

It was evaluated the technical viability of mercury removal by electrodeposition from vegetal biomass samples obtained from mining zones which had 10±0.3 µgHg g-1. Each sample was treated by mixed acid to destroy the organic matter and liberate the metal in its inorganic form for the later removal of Hg by means of a cell of electrolysis with a rotary electrode of copper as cathode. Mercury concentration was determined by Cold Vapor Atomic Absorption Spectrophotometry (CVAAS). Response surface methodology (RSM) was applied to evaluate the simple and combined effects of three independent parameters (voltage, time and concentration) on the removal efficiency and optimizing the operating conditions. Analysis of variance showed a high coefficient of determination (r2 = 0.925) indicating that the second order regression model explains 92.5 % of the variability in results. The maximum efficiency of removal (91.2 %) predicted by the model was found for the initial concentration of 1.0 µg mL-1, 66.6 mins and 34.3 V. Model Validation was carried out under the following conditions: 1.0 µg mL-1, 60 mins and 30 V, which are close to the maximum efficiency with a removal percentage of 87.1 %.

The effect of some mono-,bis -and tris-azo dyes compounds on the dissolution of mild steel in 1.0 M HCl solution was studied using weight loss and potentiodynamic polarization measurements. The inhibition efficiency was found to increase with increasing concentration of the inhibitors and with decreasing temperature. The adsorption of different azo dyes on the mild steel surface obeys the Langmuir adsorption isotherm. Polarization studies indicate that the compounds used are mixed type inhibitors. The thermodynamic functions of adsorption processes were calculated from weight loss at different temperatures data and were used to analyze the inhibitor mechanism. The surface morphology of the mild steel specimens was evaluated using SEM and EDAX analysis. To provide an evidence for the formation of the complex, UV-VIS spectra of solutions were investigated. From previous results (I.E.%, ∆Gads., SEM, EDAX and UV-VIS spectra) are likely to get into the possiblity of configure the complex on the mild steel surface.

The effect of the extract of Lupinus varius l. on corrosion of Al in 1 M NaOH solution using the weight loss technique was investigated. Lupinus varius l. extract inhibited the corrosion of Al in 1 M NaOH solution and the inhibition efficiency increased with increasing the concentration of the extract and decreased with increasing temperature. The adsorption of the inhibitor molecules on Al surface was in accordance with Langmuir and Temkin adsorption isotherms. A first-order kinetic relationship with respect to Al was obtained with and without the extract from the kinetics treatment of the data.

This paper reports an experimental study of corrosion characteristics of electroless Ni-P-TiO2 nanocomposite coatings. Coating process parameters are optimized for maximum corrosion resistance based on L9 Taguchi orthogonal design with four process parameters, viz., concentration of nickel source solution, concentration of reducing agent, concentration of TiO2 powder and bath temperature. Corrosion behavior of the electroless Ni-P-TiO2 nanocomposite coatings was evaluated in 3.5 wt.% NaCl aqueous solution by using polarization technique. Scanning electron microscope (SEM) and Energy dispersive X-ray spectroscopy (EDS) analysis were used for studying the surface morphology and chemical composition of the electroless Ni-P-TiO2 nanocomposite coatings. The results showed that incorporation of TiO2 in coating causes increasing of corrosion resistance and improves surface morphology. Finally, optimum conditions were achieved as, concentration of nickel source solution: 50 g L-1, concentration of reducing agent: 10 g L-1, concentration of TiO2 powder: 10 g L-1, and bath temperature of 85 °C.

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.