Portugaliae
Electrochimica Acta

The discoloration of the food colorant E131 (Patent Blue V) by K2S2O8 and KIO3 was investigated by spectrophotometric method. The discoloration is first order with respect to the food colorant and the oxidants. The discoloration rate constant increases with the increase in initial concentration of the oxidant and temperature; whereas discoloration decreases with the increase in concentration of E131 and chloride ion. In the presence of persulfate, Cu(II) and Fe(II) have a catalytic effect on discoloration but Ni(II) has not. The thermodynamic parameters (Ea, ∆H#, ∆S#, ∆G#) of the discoloration in the presence and absence of Cu(II) and Fe(II) are calculated.

The aim of this work was to study the effect of gadolinium content on the corrosion behavior of magnesium alloys in 1 wt.% NaCl solution at 21.5 (±0.5) °C. Four Mg-Gd alloys, namely Mg-2 wt.% Gd, Mg-5 wt.% Gd, Mg-10 wt.% Gd, and Mg-15 wt.% Gd, were studied. Weight loss measurements, potentiodynamic tests, electrochemical impedance spectroscopy, XR diffraction, and scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS) were performed on the four Mg-Gd samples. The results showed the influence of the Gd content on the corrosion behavior of these alloys in 1wt.% NaCl solution. The corrosion resistance of the Mg-Gd alloys was improved with the introduction of 10 wt.% Gd in Mg matrix. Thus, weight loss and electrochemical measurements revealed the better corrosion resistance for Mg-10 wt.% Gd alloy. Further addition of Gd exceeding 10 wt.% in a magnesium matrix reduces the corrosion resistance of Mg-alloy and induces an incremental increase in the corrosion rate.

The essential oil of Artemisia herba alba has been extracted and tested as an inhibitor of lead corrosion in 0.1 M Na2CO3 medium, using stationary and transient electrochemical techniques. The results obtained show that the essential oil of Artemisia reduces the corrosion rate. The effectiveness of inhibition increases with the oil concentration to reach 77 % with 2000 ppm. The effect of temperature was also studied.

The redox properties of the 1,10-phenanthroline containing Robson type symmetrical macrocyclic dicopper(II) complex [Cu2L(H2O.phen)2](ClO4)2 1 (L = μ-11,23-dimethyl-3,7,15,19-tetraazatricyclo-[19.3.1.18 19,13,21] he p t a c o s a-1(24) , 2, 7, 9, 11, 13(26), 14, 19, 21(25), 22-decaene-25,26-diolate) and of its dicopper(II) precursor [Cu2L(H2O)2](ClO4)2 2 have been investigated by cyclic voltammetry and controlled potential electrolysis in different organic solvents. They exhibit two consecutive reversible one-electron reductions assigned to the CuIICuII  CuICuII  CuICuI cathodic processes. The results suggest that, in solution, phenanthroline does not coordinate to the metal in complex 1, but its H-bonding interaction with the water ligands can be preserved.

Nickel coatings were obtained from Watts bath containing sodium dodecyl sulfate (SDS) or polyvinylpyrrolidone (PVP) surfactants by direct current plating. The influence of electrolysis parameters, temperature, current density, concentration of surfactants and pH on the nickel deposits brightness is investigated through a multiple linear regression model with interaction. The models obtained fitted very well the experimental data. ANOVA statistical analysis shows that all design factors are significant, and the brightness of nickel deposits obtained from bath containing PVP is more sensitive to the changes in the factors levels. The electrochemical behaviour of baths was discussed; the results revealed an inhibitive effect exerted by both SDS and PVP. We have also found that the brightness and the inhibition are well linked and directly proportional. In addition, the corrosion resistance of the nickel coatings was slightly improved, especially with PVP. Finally, the optimization analysis showed that PVP could efficiently and eco-friendly substitute SDS as an additive of nickel electroplating.

In this work, electrocoagulation (EC) was used to treat meat industry (frigorific) wastewater. Effects of EC process variables such as distance between electrodes and potential on the removal efficiency of chemical oxygen demand (COD), were examined. Two factors with three levels response surface design coupled with response surface methodology (RSM) were employed to optimize the EC process variables. Second order polynomial models were developed for the responses and three dimensional (3D) response surface plots were used to study the interactive effects of the process variables on the EC efficiency. Experimental results showed that EC treatment, using a potential of 40 V and electrodes with a 3 cm gap between them, presented a COD removal of over 90% for the meat industry wastewater.

Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were used to measure the corrosion rate of aluminium in 0.1 M HCl in the absence and presence of different concentrations of chitosan. Inhibition efficiency up to 90% in the presence of 0.028 g/L chitosan was achieved. Increasing the concentration of chitosan shifted the breakdown potential, Eb, of aluminium to more noble values and inhbitied the pitting corrosion of aluminium. Measurements of the break potential, Eb, and the electrical double layer capacity (Qdl) indicated that chitosan is adsorbed at the aluminium/solution interface.

The application of combined chemical coagulation and electrochemical oxidation processes to treat a leachate from an intermunicipal sanitary landfill was evaluated. Chemical coagulation (CC) experiments were performed with lime (Ca(OH)2), and the influence of the lime concentration, stirring speed and assay duration were studied. In the electrochemical oxidation (EO) assays, a boron-doped diamond anode was used, and two applied current intensities were tested. It was also evaluated the influence of the lime concentration used in the CC pre-treatment on the EO performance. In the CC assays, the highest COD removals were obtained for lime concentrations of 20 and 25 g L-1, at 100 rpm stirring speed, during 2 h. In the CC+EO combined treatment the highest removals were obtained at the applied current intensity of 0.6 A, being the influence of the lime concentration used in the pre-treatment almost insignificant. The highest current efficiency was obtained for the combined treatment with EO assays performed at 0.4 A.

The effect of linseed oil (LO) on the corrosion of carbon steel in 1 M HCl solution was investigated using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) technique and weight loss measurements. The inhibiting action increases with the concentration of the tested inhibitor. The highest efficiency (98.2%) is obtained at 3g/L of LO. The influence of temperature on the corrosion behavior of carbon steel in 1 M HCl, with the addition of LO was also studied. The obtained data from EIS measurements were analyzed to model the corrosion inhibition process through an appropriate equivalent circuit model; a constant phase element (CPE) has been used. Polarization measurements show also that LO acts as a good mixed inhibitor. The inhibition process is attributed to the formation of an adsorbed film of the inhibitor on the metal surface which protects the metal against corrosion. LO is adsorbed on the steel surface according to a Langmuir isotherm adsorption model. The results obtained showed that the linseed oil could serve as an effective green inhibitor of the corrosion of carbon steel in hydrochloric acid medium.

A new quaternary Ni–Fe–P–C composite coating was deposited on copper substrates by an electrodeposition process. The morphology, structure and composition of the prepared electrode were characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD) pattern, and energy dispersive X-ray spectroscopy (EDX). The activity of the composite coating toward hydrogen evolution reaction (HER) was evaluated on the basis of the steady-state polarization Tafel curves and electrochemical impedance spectroscopy (EIS) in 1 M NaOH at temperature of 298 K. The experimental results revealed that the HER activity of the Ni Fe P C coatings was enhanced compared with both ternary coatings of Ni P C and Ni-Fe C. The source of its activity was found from its high surface area and its intrinsic properties. It was sufficient to assume the Volmer–Heyrovský mechanism with the Heyrovský reaction as the rate-determining step to explain the experimental data. Besides the high electrocatalytic activity, excellent chemical and electrochemical stability were observed for Ni Fe P C composite coating toward the HER in 1 M NaOH at 298 K.

The present research article deals with the study of corrosion behavior of Ni-P-TiO2 composite coating. The TiO2 composite coating is deposited on the mild steel substrate. Corrosion behavior of the TiO2 composite coatings after heat treatment at various annealing temperatures (300 °C, 400 °C, and 500 °C) is evaluated with the help of potentiodynamic polarization test using 3.5% NaCl solution. The electrochemical parameters, corrosion potential (Ecorr) and corrosion current density (Icorr), are optimized for maximum corrosion resistance using Taguchi based grey relational analysis. The coating parameters, namely, nickel sulphate, sodium hypophosphite, concentration of TiO2 particles and annealing temperature are considered as main design factors. The analysis of variance (ANOVA) revealed that the annealing temperature and concentration of TiO2 particles have significant influence on the corrosion behavior of the composite coating. The microstructure characterization of the coating is conducted using scanning electron microscopy, energy dispersive X-ray analysis and X-ray diffraction analysis. The Ni-P-TiO2 composite coating exhibits nodular structure with uniform incorporation of titanium particles and converts into the crystalline structure after heat treatment.

The aim of present study is to establish the not known divalent state of praseodymium and samarium in non-aqueous medium at 298.15 K and atmospheric pressure. Potentiostatic and galvanostatic methods were used to characterize the divalent states of both lanthanides. Under the specified experimental conditions, samarium and praseodymium showed two reduction steps at glassy carbon electrode in non-aqueous medium. Cathodic and corresponding anodic peak potential and peak currents were calculated for samarium and praseodymium ions at different scan rates. The results also suggest that the scan rate has great influence on the behaviour of both lanthanides. Diffusion coefficient (D x cm2/sec) and heterogeneous forward rate constant (kºfhxcm/sec) have been evaluated. Transition time (tau) has also been evaluated for Pr(III)/Pr(II), Pr(II)/Pr(0) coupled systems, suggesting that the system is approaching from irreversible with increasing the scan rates. The effects of changing the scan rate and donor number on the electrochemical behavior of both lanthanides have been examined at 298.15 K and atmospheric pressure.

Concrete is one of the most widely used engineering materials for construction. Its durability is a major problem affecting the service life of the engineering structures. Various technologies such as cathodic protection and the use of corrosion inhibitors are used to improve the durability of reinforced concrete. Various organic and inorganic inhibitors, and also extracts of natural products have been used as corrosion inhibitors. Corrosion resistance of rebars has been evaluated by electrochemical studies such as polarization study and AC impedance spectra. The protective films formed on the metal surface have been analyzed by NMR, FTIR spectra, SEM, AFM and XRD.

The electrochemical corrosion behaviour of an electrodeposited Ni–28wt.%Al composite coating was characterized after 24 h and 72 h immersion periods in 3.5% NaCl solution, using electrochemical and surface probe techniques. Open circuit potential (OCP) and potentiodynamic polarization revealed that the Al particles modify the electrochemical corrosion behaviour of the Ni coating by shifting its EOCP more negatively and increasing its anodic dissolution current density, after 24 h immersion in 3.5% NaCl solution. Compared with the Ni coating, the composite can exhibit well–reduced anodic current density and slightly increased cathodic current with immersion up to 72 h. XPS characterization showed that a high rate of water adsorption and rapid formation of a continuous Ni(OH)2 initially occurs on the composite surface which, however, readily thickens during prolonged immersion time and promotes the corrosion product enrichment with Al2O3. This greatly decreased the rate of corrosion and susceptibility to pitting for the Ni–28wt.%Al composite after 72 h immersion in 3.5% NaCl solution.

Five different water soluble terpolymers, namely polyvinyl alcohol-g-poly(acrylamide-vinylsulfonate), polyvinyl alcohol-g-poly(acrylic acid-vinylsulfonate), polyvinyl alcohol-g-poly(acrylamide-vinyl benzene sulfonate), polyvinyl alcohol-g-poly(acrylic acid-vinyl benzene sulfonate) and polyvinyl alcohol-g-poly(vinylsulfonate-vinyl benzene sulfonate), have been designed, developed and tested for their efficacy to control N-80 steel corrosion in 10 % HCl, 3.5 % NaCl and simulated well water. The terpolymer characterization was carried out by FTIR. The inhibitors were tested by potentiodynamic and impedance techniques. The inhibitors were also tested in static and dynamic conditions at 55±5 °C, for 6 hours immersion period by weight loss method. Acrylamide terpolymers rendered the best inhibition efficiency in all the studied systems. The results provided a preliminary validation of the inhibitor such that they can be optimised and used for corrosion in oil and gas industries.

Anodic limiting currents were measured in an unstirred divided cell at an inclined small scale anode using a large scale cathode with angles of inclination from vertical axis as 45, 60 and 75°. Anode heights (II) vary from 1 cm to 6 cm and phosphoric acid concentration from 6 to 10 moles. Limiting currents for electropolishing of copper were between 5 and 58 mA.cm-2 depending on the operating conditions. A general correlation of data of all inclinations was obtained using the equation: I = 28.57(Ɵ 0.520.C -0.89.H -0.91) (1) with an average deviation of ±4%.

Cobalt impregnated zeolite-modified electrode was prepared by mixing cobalt–zeolite (Co–Z) and graphite powder with different percentages. Using the cyclic voltammetric technique, the electrochemical oxidation of hydrogen peroxide at such electrodes was investigated. Experiments on zeolite show that it is not electrochemically active towards hydrogen peroxide oxidation in NaOH solution. The presence of cobalt ions in the zeolite matrix, by soaking the electrode in an aqueous Co(NO3)2 solution, markedly enhances the electrocatalytic activity which was found to depend on the cobalt content. On the other hand, the presence of zeolite and/or Co metals in the catalyst is essential; however, the electro-catalytic activity depends on different percentages of Co–Z. Under the selected conditions, the anodic peak current was linearly dependent on the concentration of the hydrogen peroxide in the range 0.03–9 and 0.006-0.1 mM with CV and amperometric methods, respectively. The detection limits (S/N=3) were also estimated to be 17 and 2.5 µM.

Electrochemical reduction of boron from boron containing fluoroborate species present in KCl (81.54 mol%)-KF (18.45 mol%)-NaBF4 (1.67x10-4 mol cm-4) melt on a platinum electrode was studied by cyclic voltammetry and chronoamperometry. These studies were carried out over the temperature range 1073 - 1123 K. Boron-containing electroactive species is shown to reduce quasi-reversibly at low scan rates (ν < 0.1 Vs-1) and irreversibly at higher scan rates (> 0.1 V s-1) through a single-step three-electron process (B(III) + 3e → B). The transfer and diffusion coefficients of the electroactive species was measured for sodium fluoroborate in KCl-KF melt over the temperature range 1073-1123 K.

The inhibitive effect of Lupine extract on the corrosion of etched and non-etched aluminum in aqueous solution of 0.1 M HCl was investigated at 30 ºC by potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and optical microscopic techniques. Potentiodynamic polarization curves indicated that Lupine extract acts as anodic type inhibitor. EIS measurements showed that the charge transfer resistance and consequently the inhibition efficiency increase with increasing concentration of Lupine. The experimental data indicated that Lupine is more efficient as inhibitor for the acid corrosion of non-etched aluminum. The inhibitive effect of the extract was assumed to occur via adsorption of active ingredients of the extract on the metal surface. Theoretical fitting of the data to the Kinetic-thermodynamic model were tested to clarify the nature of adsorption. The optical micrographs obtained after surface pre-treatment show that alkaline etching reveals the surface to be porous-like in structure and both the acid and extract have limited effect on the size of pores.