Portugaliae
Electrochimica Acta

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.

The eco-friendly ionic liquid 1-(2-ethoxy-2-oxoethyl) pyridazinium chloride's (EOPC) newly synthesised electro-oxidation behaviors of boron-doped diamond (BDD) and SnO2 in an alkaline media were compared using galvanostatic electrolysis. Various pyridazinium and alkaline concentrations were studied. In addition, the temperature, and density current effect of pyridazinium oxidation were investigated. The BDD showed a higher activity toward pyridazinium oxidation than the SnO2. This is mainly due to the higher characteristics and the relatively inert nature of the BDD. The bulk electrolysis tests have shown that the complete removal of COD can only be achieved using a boron-doped diamond and that SnO2 only permits a partial oxidation of pyridazinium. On the basis of the chemical oxygen demand (COD) evolution released during the treatment, a total mineralization has been proposed. Finally, electrolysis has been performed in the presence of NaCl. Based on these results, it is concluded that BDD has less poisoning effects and higher activity than SnO2 for the selective electro-oxidation of pyridazinium.

Solar cells (Gratzel cells) have been highly regarded due to their extremely efficient and low-cost process of converting sun light into electricity. In this work screen printed electrodes were fabricated by spraying organic and organometallic dyes on glass and flexible aluminum foil. These solar cells were prepared based on three dyes, namely nickel Di thiocyanato bis(triphenyl phosphine), nickel Dimethylglyoxime and Nile blue, and the performance of these dye-sensitized solar cells (DSSC) has been experimentally evaluated. The solar cells were fabricated using thin TiO2 films; these films were characterized by FTIR. The dyes were characterized using UV–Vis and typical J-V and P-V curves of the cells. The best performance was obtained for the mixture of nickel Dithiocyanatobis (triphenyl phosphine) and Nile blue with an open circuit voltage (Voc) of 976 mV using an incident irradiation of 100 mW/cm2 at 25 ºC.

The corrosion inhibition of mild steel in hydrochloric acid by polyvinyl alcohol-g-poly(acrylamide-vinyl sulfonate) has been studied by weight loss and electrochemical methods (AC impedance and DC polarisation) techniques in the temperature range of 303 – 343 K. The inhibitor was found to provide an excellent efficiency of more than 90 %. Various adsorption isotherms have been employed for fitting the obtained results to confirm the mode of adsorption of the grafted terpolymer on mild steel. Thermodynamic parameters of adsorption such as equilibrium constant, Gibbs free energy, adsorption heat and adsorption entropy were evaluated and discussed. Various parameters that determine the kinetics of mild steel dissolution such as activation energy, enthalpy and entropy were also calculated. Results obtained from various techniques were comparable and suggest that the terpolymer follows chemical adsorption mode for inhibition.

Electroless nickel composite coatings are developed by incorporating soft/hard particles into Ni-P coatings, to improve mechanical as well as tribological properties. The objective of the present work is to investigate the effect of various coating process parameters on the corrosion behavior of Ni–P–Al2O3 composite coating deposited on mild steel substrate. The electrochemical impedance spectroscopy test is used to evaluate the corrosion behavior of the heat treated composite coatings at various annealing temperatures (300 °C, 400 °C, and 500 °C). Corrosion properties, charge transfer resistance (Rct) and double layer capacitance (Cdl), are optimized using Taguchi based grey relational analysis to improve the corrosion resistance of the coating. Concentration of nickel source, concentration of reducing agent, concentration of alumina particles and annealing temperature, are considered as a main design factor for optimization of electrochemical properties. Analysis of variance (ANOVA) is used to find out the optimum combination of coating process parameters. From ANOVA result, it is found that the concentration of Al2O3 particles and annealing temperature have significant influence on the corrosion resistance of the composite coatings. Concentration of reducing agent has moderate influence on the corrosion resistance. Surface morphology of the coated surface is studied using SEM (scanning electron microscopy) and chemical composition of the coating is studied using EDX (energy dispersive X-ray analysis). The XRD (X–ray diffraction analysis) is used to understand the phase transformation behavior of the composite coatings.

In this paper, a glassy carbon electrode is modified by Bismuth-Chitosan (Bi-Chit) nanosheets. Bismuth, that is “environmentally friendlier” than mercury, is deposited on a glassy carbon electrode by electrolysis at - 0.75 V vs. SCE in a stirring solution containing 0.18 mg mL-1 Bi(NO3)3, 0.05 mg mL-1 KBr and acetate buffer 0.1 M (pH=4.5) for 200 s. Furthermore, the electrode is modified by chitosan by the means of sonication of bismuth-modified glassy carbon electrode in chitosan solution for 15 minutes. Study of the field emission by scanning electron microscopy (SEM) shows the formation of Bi-Chit nanosheets on the glassy carbon electrode. The modified electrode surface is also characterized by energy dispersive X-ray analysis (EDX). In this research the Bi-Chit modified glassy carbon electrode exhibits excellent catalytic activity toward the electro-reduction of Tartrazine. The modified electrode is successfully used for determination and measurement of Tartrazine in Bisacodyle tablets and chocolates with colorful coatings.

The objective of this study is the valorization of the essential oil (EO) of Lippia citriodora irrigated by urban wastewater from the city of Settat-Morocco. We have tested it as a corrosion inhibitor of aluminum in 0.1 M Na2CO3 using polarization method, weight loss, and EIS measurements. The inhibition efficiency of lippia citriodora oil was calculated and compared. We found good agreement between the referred methods. The results obtained revealed that the tested inhibitor reduces differently the kinetic of the corrosion process of aluminum. Its efficiency increases with the concentration and attained 90.33% at 1800 ppm. The effect of temperature on the corrosion behaviour of aluminum in 0.1 M Na2CO3 was also studied in the range 283 K and 313 K. The thermodynamic data of activation were determined. The analysis of Lippia citriodora oil, obtained by hydro-distillation, using gas chromatography (GC), showed that the major components are neral 13.85%, geranial 14.06% and limonene 28.32%.

The corrosion inhibition and adsorption of ethanol extracts of leaves (LV), stems (ST) and roots (RT) of Rotula aquatica plant for mild steel in H2SO4 solutions were investigated using conventional weight loss, gasometric techniques, electrochemical polarizations and electrochemical impedance spectroscopy. The results showed that all the three extracts of Rotula aquatica plant performed well as inhibitor for the corrosion of steel in sulphuric acid media and the inhibition efficiencies of the extract follow the trend RT > LV > ST. Inhibition efficiencies increased with increasing concentration of the plant extracts but decreased with the temperature rise for all cases. Both the cathodic hydrogen evolution and the anodic dissolution of mild steel were inhibited, hence the active molecules of all the extracts studied acted as mixed type corrosion inhibitors.

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 were measured for sodium fluoroborate in KCl-KF melt over the temperature range 1073 – 1123 K.

Inhibition effect of poly 3-dodecyloxy aniline polymeric surfactant (PC12H) on the corrosion of aluminum in 0.5 M HCl solution was investigated using potentiodynamic polarization technique under different experimental conditions. Inhibition efficiency and thermodynamic functions for dissolution and adsorption of PC12H are compared with Poly 3-(dodecyloxy sulfonic acid) aniline (PC12SO3H) to explain the effect of terminal side chain on the corrosion protection. Data show that the presence of –SO3H as a terminal group in PC12SO3H decreases the inhibition efficiency from 88.7%, in case of PC12H, to 55.1% in case of PC12SO3H. Quantum chemical calculations were performed on PC12H and PC12SO3H to investigate the relationship between the molecular structures and their inhibition efficiencies.

The present article considers an experimental study of tribo-corrosion behavior of electroless Ni–P coatings in alkaline environment sliding against alumina. The study of wear and friction behaviour is carried out using different load and sliding speed with the help of a pin-on-disk tribometer. The wear rate increases with decrease in sliding speed and increase in the applied load. The friction coefficient initially decreases with increase in the applied load and then remains at nearly steady level at higher applied load. Also, it is found that the friction coefficient is lower at higher sliding speed. The friction coefficient does not change with the sliding duration after the initial transient running-in time. The coating is characterized using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis and X-ray diffraction (XRD) analysis. The wear mechanism is also studied and has been found to be mostly abrasive in nature.

The inhibitive effect of aqueous extract of leaves of Polyalthia longifolia on the corrosion of mild steel was studied using the gravimetric (weight loss) method at the temperatures 303 and 318 K. The results show that the aqueous extract of Polyalthia longifolia leaves inhibited the corrosion of mild steel in dilute H2SO4 solution. It was found that the inhibition efficiency increased with inhibitor concentration and decreased with rise in temperature. Values of the activation energy of the inhibited corrosion reaction range between 45.40 kJ/mol and 62.22 kJ/mol. This is much higher than the 25.74 kJ/mol obtained for the blank. The adsorption of the extract was spontaneous and occurs according to Flory-Huggins adsorption isotherm. The corrosion inhibition of Polyalthia longifolia leaves extract was attributed to the adsorption of phytochemical molecules present in the extract onto the surface of the mild steel. Physical adsorption mechanism has been proposed for the adsorption of the inhibitor.