Portugaliae
Electrochimica Acta

Benzaldehyde oxime can be readily converted to the corresponding benzaldehyde in biphasic medium. The reaction was carried out with platinum electrodes at room temperature in an undivided cell within constant biphasic medium consisting of chloroform containing benzaldehyde oxime and an aqueous solution of potassium perchlorate as a mediator with a catalytic amount of H2SO4. The electrochemical oxidation was optimized with various experimental parameters to result in the high yield of benzaldehyde (80%).

Bitter leaves extract as inhibitive agent in HCl medium for the treatment of mild steel through pickling was studied. Thermometric, gravimetric and potentiodynamic polarization methods were employed in the corrosion inhibition study. The bitter leaves extract was analyzed using gas chromatography-mass spectrometer. The analysis of the extract revealed the presence of C6H8O (96 g/mole: 2,4-Hexadienal); C7H12 (96 g/mole: 3,4-Heptadiene; 1,3-Diethylallene) and C10H18O2 (170 g/mole: 2-Decenoic acid) as the predominant chemical constituents. The activation energy for the corrosion inhibition process ranged from 39.831 to 77.533 kJ/mol, while the heat of adsorption ranged from -16.093 to -30.224 kJ/mol. These values showed that exothermic and spontaneous adsorption of the extract on the mild steel followed the mechanism of physical adsorption. Maximum inhibition efficiency of 85.4% was obtained. The extract was highly efficient in the corrosion inhibition function. The plant-based inhibitor of bitter leaves extract is a suitable additive for pickling, cleaning and descaling operations.

We made a nano-porous alumina membrane by anodization under 40 V by two steps (10 minutes and 120 minutes) in oxalic acid, followed by chemical treatment in phosphoric acid assisted by an ultrasonic bath. Thus, we achieved a total relatively short time (3 h 30 min) for the synthesis, having all physicochemical processes been done at room temperature (25 °C). We verified a hexagonal arrangement structure with 56 nm inter-pore diameter, and density of 1010 pores/cm2, characteristic of the self-ordered porous alumina. Therefore, our membranes can be used as a template for fast synthesis of nanostructures as nanowires, nano-tubes.

Aluminum alloy corrosion behavior (AA6063) in a 0.5 M hydrochloric acid (HCl) solution was studied. It has been observed that the ethanolic extract of Cordia dichotoma seeds (EECdS) acts as an excellent inhibitor for AA6063 corrosion in a 0.5 M HCl solution. In this study, conventional weight loss, Fourier transformed infra-red spectroscopy (FTIR), electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM) analysis techniques were used. It was found that the percentage inhibition efficiency increased with higher CdS concentrations. The thermodynamic and kinetic parameters, along with the equilibrium constant for the adsorption processes, showed that CdS performed well as an inhibitor. CdS adsorption on the alloy followed the Langmuir adsorption isotherm, at all the studied concentrations. FTIR, EIS and SEM investigations also indicated that CdS presence effectively lowered the dissolution currents.

N1,N2-Bis(1-Phenylethylidene)ethane-1,2-diamine (PEED) was tested as a corrosion inhibitor for C-steel in a 1.0 M HCl solution, by using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results showed that PEED is a very good inhibitor, as its inhibition efficiency reached 93.8 %, with a concentration of 1.0x10-3 M, at 298 K. Tafel polarization study revealed that PEED acted as a mixed type inhibitor that obeyed Langmuir adsorption isotherm. The thermodynamic activation parameters for the corrosion reaction were calculated and discussed. Quantum chemical parameters and Fukui function were obtained by DMol3/GGA/PW91/DNP+ level of theory, which was performed using Materials Studiov 8.0 software from Biovia-Accelrys. Monte Carlo simulation was implemented to search for the equilibrium configurations of the PEED/Fe(111) adsorption system, in a 1.0 M hydrochloric acid solution.

Conducting polypyrrole was synthesized by the chemical oxidative method, and characterized using FTIR spectroscopy. An epoxy based paint containing conducting polypyrrole was prepared and applied on a low carbon steel sample, using a film applicator. The uncoated and painted steel samples were kept immersed in the simulated concrete pore solution. The Mott-Schottky technique was used to study the passive film formation on an uncoated low carbon steel, and the conducting polypyrrole coated low carbon steel was immersed in a simulated pore solution. The peaks at 1447 cm-1 and 1149 cm-1 are the responsible peaks of protonated nitrogen atoms in polypyrrole. The peak at 1538 cm-1 refers to the C-C stretching vibration in the pyrrole ring, and the peak at 1042 cm-1 denotes the C-H stretching vibration in the pyrrole ring. The M-S slope indicates that the passive film on uncoated low carbon steel exhibited n-type semi-conductive behaviour, and that the polypyrrole coating exhibited p- n type behaviour. However, with the increasing chloride contents and immersion time, the polypyrrole coating exhibited only p type behaviour.

The efficiency of Commelina benghalensis leaves extract as a mild steel corrosion inhibitor in hydrochloric acid (HCl) and sulphuric acid (H2SO4) has been evaluated. The corrosion rates were determined using the gravimetric (weight loss) and electrochemical techniques. The results obtained in the absence and presence of Commelina benghalensis extracts were used to calculate the inhibition efficiency (%), and to propose the inhibition mechanism and adsorption type. The obtained results showed that the inhibition efficiency increased with the increase in concentration of Commelina benghalensis extract. The phenomenon of chemical adsorption was proposed, and the inhibitor adsorption was found to obey Langmuir, Temkin and kinetic thermodynamic models. The polarization study reveals that, in the inhibitor presence, the corrosion current value decreases, indicating the formation of a protective film on the metal surface, which prevents the electron release from it.

The study of tropical fruits’ nutraceutical properties has been of great interest in the food research area. There are several parameters traditionally used to make fruits quality control, such as organoleptic analysis and physical and chemical assays. This work proposes the use of a simple, fast and low cost electrochemical technique for the characterization of fruit extracts in function of their ripening state, using as biological model a tropical fruit commonly named as Mortiño (Vaccinium meridionale swart). Cyclic voltammetry was selected as an electrochemical technique, due to the possibility of extracting kinetic and thermodynamic information from the results. A good correlation between the fruit extract’s physical-chemical properties and electrochemical parameters, such as peak intensity, charge and oxidation peak potential, was obtained.

In the chemical synthesis of polypyrrole (PPy), pyrrole oxidative polymerization was done. The use of alkali salts viz. FeCl3, Fe(NO3)3, as an oxidative polymerizer, creates impurities, affecting the purity of formed PPy. In this work, highly pristine PPy flexible electrodes (FE) were chemically synthesized using a 0.1 M solution of pyrrole acidified with 0.05 M HClO4 and 30 wt % H2O2, by the successive ionic layer adsorption and reaction (SILAR) method. FEs XRD patterns indicate amorphous PPy formation. A characteristic peak at 1559 cm-1 in the FTIR spectra confirms PPy formation. A gradual change in the surface morphology with SILAR immersion time was observed. Nyquist plots describe different impedance parameters, which vary with SILAR immersion times. In cyclic voltammetric analysis (CV), the maximum specific capacitance observed for the FEs prepared with an immersion time of 10 s was 520.48 Fg-1. Specific capacitance calculated using the galvanostatic charge discharge (GCD) analyses was 529.70 Fg-1, which was nearly the same as that observed by CV. FEs exhibited great cycling stability, even after 5000 cycles, with 74.43% of capacitance retention. Solid state symmetric device (SSD) produced specific capacitance as high as 312.28 Fg-1, with 76 % of retention, even after 5000 cycles.

In this paper, corrosion resistance was compared between molybdate conversion coatings containing SiO2 or TiO2 nanoparticles, on five magnesium alloys exposed to a 3.5 wt.% NaCl solution. The surface morphology of the molybdate conversion coatings containing SiO2 or TiO2 nanoparticles was examined by scanning electron microscopy (SEM). The corrosion resistance of the nanocoatings was investigated by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and potentiodynamic cyclic anodic polarization measurements. The electrochemical methods showed that the addition of SiO2 or TiO2 nanoparticles to the conversion treatment has significantly improved the corrosion resistance property of molybdate conversion coatings for all tested Mg alloys, but revealed that TiO2 was more effective.

Cysteine’s action on 3003 aluminum alloy dissolution in a 2% NaCl solution, at different pH values, has been investigated. Weight-loss measurements, potentiodynamic polarization and electrochemical impedance at OCP were performed. The surface morphology was analyzed by SEM. The main results showed that the alloy underwent severe corrosion at 2 and 11 pH values, as compared to at 5 and 8 pH values. Furthermore, a duality effect of cysteine was noted, as it acted as a corrosion inhibitor or accelerator, depending on its concentration, and on the solution’s pH value. This particular behavior can be related to the instability of the formed film adsorbed onto the metal surface. All these findings show the high complexity of cysteine action on 3003 aluminum alloy, under the investigated conditions.

Three quaternary ammonium bromides were investigated as mild steel corrosion inhibitors in 1 M HCl. Two investigation methods were applied: electrochemical impedance spectroscopy (EIS) and polarization resistance (Rp method). The experimental impedance data showed capacitance frequency distribution, which imposed the introduction of a constant phase element, instead of a pure capacitance. Adequate structural models were advanced, to describe the interfacial processes. The models parameters values were determined. The resistance values found by impedance spectroscopy were compared to those of the polarization resistance provided by the Rp method. The inhibition efficiency of the investigated compounds was evaluated by both applied methods. The comparison of the investigated compounds’ protective properties outlined the best among them.

Catechol, which underwent electrochemical oxidation to produce o-benzoquinone, as Michael acceptor, taking part in a nucleophilic attack by dimethylamine, has been studied in an aqueous solution, with various pH values, different electrodes and different dimethylamine concentrations, using cyclic voltammetry, controlled potential coulometry and differential pulse voltammetry. The participation of o-benzoquinone reaction with dimethylamine, at higher nucleophiles concentrations, in the second potential’s scan, was observed. The products generated from the reaction were assumed to be 4-(dimethylamino)benzene-1,2-diol, which underwent electrons transfer at more negative potentials than those from catechol. Catechol pH effect, in dimethylamine presence, was studied by varying pH values from 3 to 9. The reaction was strongly influenced by pH, as well as by dimethylamine concentration. The reaction was mostly favorable in 150 mM of dimethylamine and 2 mM of catechol in a neutral medium. In both acidic and basic conditions, the reaction was not favored, due to amine protonation and hydroxylation. The reaction mechanism was of the ECE type, followed by the diffusion process.

The electrocatalytic property of electrode materials is the key for getting high cell current and low overvoltage of a fuel cell from fuels electro-oxidation. The bridge between laboratory scale fuel cell development and its fully commercialization is the development of inexpensive but energetic electrode materials. The catalytic actions of an electrode substrate are strongly influenced by the morphology and the grain fineness of the deposited materials. The present investigation aims at finding the effect of electrode deposition mode viz. direct current and pulse current coating, to produce an electrodeposited substrate that can deliver the highest current in a direct ethanol fuel cell. Nickel (Ni) is one of such non precious materials which has been produced through electro synthesis by both pulse current (PC) and direct current (DC) coating. It has been found that the morphology of the deposited is highly influenced by the current density, duty cycle, electrolyte chemistry and right selection of deposition potential on the cathodic polarization curve around the Tafel lines. Electrochemical characterization has been done by cyclic voltammetry (CV), chronoamperometry (CA) and potentiodynamic polarization (PD) studies. The substrate of the electrodeposited material has also been characterized by X-Ray Diffraction analysis (XRD), Energy Dispersive X-Ray Analysis (EDXA) and Scanning Electron Microscope (SEM). It has also been found that the electro synthesis by pulse current coating at pre-selected deposition potential, right at the end of Tafel region, at 40 ºC temperature and 150 second deposition time, gives the highest delivering current of ethanol fuel oxidation.

The inhibiting effect of Ailanthus altissima aqueous extract, as a corrosion inhibitor for Zn in a 0.5 M HCl solution, has been evaluated by weight loss (WL), hydrogen evolution (HE), potentiodynamic polarization (PP), electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. Obtained results showed that this extract offered good protection against Zn corrosion, and exhibited high inhibition efficiencies. The IE was found to increase with an increasing extract dose. Results revealed that this extract acted as a mixed-type inhibitor, and adsorbed onto the Zn surface following Temkin isotherm. Obtained results were justified from the study of surface morphology.

This paper deals with the theory and kinetics of oxalic acid electrochemical oxidation, in an acidic solution containing sodium chloride, using a manganese dioxide rotating cylinder anode. Voltammetric and galvanostatic electrolysis techniques were used. The voltametric study shows a higher anodic wave corresponding to chlorine oxidation on the MnO2 electrode, prevailing oxalic acid indirect oxidation. Galvanostatic electrolysis studies confirmed that the rate constant is affected by chloride concentration, current density, agitation and temperature. Electrochemical oxidation rate was found to be a pseudo-first order kinetic process. A strongly linear relationship between the rate constant and chloride concentration was observed, while polynomial relations, with respect to current density and temperature, were found. The activation energy was found to be 14.541 kJ/mol, which suggests a diffusion control kinetic step in oxalic acid degradation. The findings of the present research validate that oxalic acid incineration can be successfully carried out on a MnO2 anode, in NaCl presence.

Thymus Sahraouian essential oil (TSEO), as a new corrosion eco-friendly inhibitor, has been used to protect mild steel in 1 M HCl. Weight loss, three potentiodynamic polarization methods (Tafel, Stern and Stern-Geary), and electrochemical impedance spectroscopy measurements were undertaken to evaluate corrosion inhibition by TSEO. TSEO acted as an efficient corrosion inhibitor for mild steel in 1 M HCl, and its inhibition efficiency increased with a concentration of 77.82 % at 2 g L-1. The polarization curves revealed that TSEO acted as a mixed type inhibitor, with predominant anodic action. The EIS studies were fitted to a suitable equivalent circuit model, at 293 K, only reflecting a one-time constant characteristic of a charge transfer process. Besides, the higher is the temperature the lowest is the inhibiting efficiency. The kinetic parameters were in favour of an electrostatic character of TSEO components adsorption onto the mild steel surface, and adsorption followed the Langmuir isotherm model. Micrographic scanning electron microscopy and energy dispersive X-ray spectroscopy analyses confirmed the formation of a protective adsorbed film upon the mild steel surface.

Conducting polypyrrole was synthesized, and applied with a paint coating on a low carbon steel sample. By using linear polarization technique, the corrosion rates of uncoated and painted low carbon steel samples, in 3.5 wt% NaCl, were determined, and found to be 5 mpy and 0.1 mpy, respectively. The uncoated and conducting polypyrrole coated steel samples were immersed in a simulated carbonated concrete pore solution, and electrochemical studies were carried out. The shift of corrosion potential in the positive direction implies that the polypyrrole coating gives corrosion protection to low carbon steel, in the anodic direction. As compared to uncoated low carbon samples, polypyrrole coated low carbon steel samples exhibited higher impedance values, but their corrosion resistance decreased with increasing chloride ions in a carbonated pore solution.

This work investigates the effectiveness of the ethanol extract of Phyllanthus amarus (EEPA) as a possible green corrosion inhibitor for aluminum in a HCl solution, using weight loss, linear and potentiodynamic polarization methods, in order to evaluate the inhibition efficiencies of the plant extract, at various concentrations. Scanning electron microscopy and Fourier transformed infra red spectroscopy were used to study the surface morphology and engagement of functional groups in the corrosion inhibition process. The results obtained at 303 K from weight loss, linear polarization resistance and potentiodynamic polarization methods recorded an inhibition efficiency that ranged from 56.65 to 69.17, 65.00 to 93.93 and from 51.38 to 79.96 %, respectively. Generally, the inhibition efficiency increased with higher concentrations, but decreased with a rise in temperature. The potentiodynamic study revealed that EEPA acted as a mixed type inhibitor, and formed an insoluble film, which protected the metal against corrosion. Examination of micrographs in the inhibitor presence and absence also confirmed the role of the protective film in blocking the corrosion active sites on the metal surface. Spectra analysis obtained from Fourier transformed infra-red study indicated that EEPA was adsorbed onto the aluminum surface via C=O and OH functional groups. The inhibitor adsorption was spontaneous, exothermic, and supported the physical adsorption mechanism. Calculated quantum chemical parameters for EEPA constituents revealed that Phyllanthusin D is the most active corrosion inhibitor in the compound. HOMO and LUMO diagrams of Phyllanthusin D supported the findings from FTIR analysis.

In the present work, we present the first study about the effect of Chamaerops humilis L. extract on the behavior of reinforcement steel in a carbonated concrete pore solution (pH≈9). This study has been realized using electrochemical measurements: open circuit potential (OCP) and electrochemical impedance spectroscopy (EIS). The phytochemical screening was used to reveal the presence of some phyto-constituents in the plant extract. The Folin–Ciocalteu method and the AlCl3 coloration were used to determine the total phenolic and flavonoid contents, respectively. Results show that the plant extract has a beneficial effect on the development of a passive layer. The extract plays an important role in the corrosion potential evolution, and in the polarization resistance increase. The inhibition efficiency of the plant extract is close to 60% at a concentration of 0.75 g/L. Corrosion parameters also changed with exposure time.