Portugaliae
Electrochimica Acta

The electro active inorganic-organic nanohybrid material Polyaniline-BaMnO3 has been synthesized by the surfactant assisted chemical polymerization reaction of aniline with nanocrystalline BaMnO3. Electrochemical studies have been performed using cyclic voltammetry and galvanostatic charge-discharge measurements. The enhanced electrode performance originates from the synergistic effect of PANI and BaMnO3. The hybrid delivers very high specific capacitance of 560.5 Fg-1, energy density of 32.01 whkg-1 and power density of 400 wkg-1, respectively. The hybrid also exhibits very high stability and excellent cycling performance with less than 5% capacity loss over 500 cycles.

New quinoline, namely 5-(ethoxymethyl)-8-quinolinol (M-QN), has been synthesized and characterized by different spectral methods, such as 1H NMR, <13C NMR and IR spectra. Its inhibitive action against the corrosion of carbon steel in 1.0 M hydrochloric acid solution was investigated at different temperatures in the range from 25±2 to 55±2 °C by a series of known techniques, such as weight loss, open circuit potential (OCP), electrochemical impedance spectroscopy (EIS) and Tafel polarization measurements. The inhibition efficiencies obtained from all employed methods are in good agreement with each other. The obtained results show that M-QN compound is a very good inhibitor with an efficiency of 97.7 % at 10-3 M additive concentration in a 1.0 M HCl solution. The inhibition efficiency increased with an increase of the inhibitor’s concentration. Changes in impedance parameters (Rct and Cdl) were indicative of adsorption of the compound (M-QN) on the metal surface, leading to the formation of a protective film. Tafel polarization measurements showed that M-QN inhibitor is of a mixed type. The adsorption of the inhibitor on the surface of carbon steel in a 1.0 M HCl solution was found to obey Langmuir’s adsorption isotherm. The kinetic and thermodynamic parameters for carbon steel corrosion and inhibitor adsorption, respectively, were determined and discussed. On the bases of thermodynamic adsorption parameters, comprehensive adsorption (physisorption and chemisorption) for the studied inhibitors on carbon steel surface was suggested.

Long term wet corrosion resistance of metals depends on the stability of their corrosion product layer. With immersion corrosion tests, such stability can be predicted. EIS and potentiodynamic polarization were complemented with XPS to investigate the characteristics of Ni corrosion product layer formed after 1 hr. and 72 hr. immersion in 3.5% NaCl solution. Two time constants with decreasing Nyquist semi-circle size and phase angle maxima, based on EIS characterization during the immersion times, indicated the formation of an increasingly porous and less adherent corrosion product layer. The product formation shifted the Ni corrosion potential more negatively and increased cathodic and anodic current densities, during potentiodynamic polarization. XPS characterization suggested that a rapid nucleation of NiO could increase H2O adsorption, subsequently triggering the formation of different forms of Ni(OH)2 in the corrosion product layer. Consequently, the corrosion resistance of the Ni coating decreased after 72 hr. immersion in 3.5% NaCl solution.

An algorithm is presented for the calculation of corrosion parameters with mixed charge-transfer and diffusion control, based on the polynomial method, and having good accuracy and precision.

The feasibility of using extract of Grewa Venusta (wild jute tree) root as corrosion inhibitor with mild steel was investigated using gravimetric and electrochemical techniques in 1.0 M hydrochloric acid. The inhibitor’s concentration, temperature and time were varied in the range of 0-10% v/v at 2% v/v interval, 30 - 75 oC at 15 oC interval and 1-6 hours at 1 hour interval. Characterizations of the extract were done by quantitative method (AAS) and Gas Chromatography-Mass Spectrometry (GC-MS). Scanning electron microscope (SEM) was used to analyze the surface morphology of the samples. The synergetic effect of the inhibitor was evaluated by addition of halide ions (KBr-, KCl and KI-). The results showed that corrosion rate increased with an increase in temperature, and decreased with an increase in inhibitor’s concentration and time; maximum inhibition efficiency was 97.60% and 99.88% in the presence of KI- addition, and was assumed to occur via adsorption of the inhibitor molecules on the metal surface. The extract contains metallic elements such as calcium, magnesium, mono acetate (C5H10O4) and 4H-Pyrazole (C9H10F6N2S) that suppressed the anodic dissolution. The adsorption of the extract molecules on the mild steel surface obeys Langmuir adsorption isotherm. The results showed that the inhibitor acted as a mixed-type inhibitor.

The inhibition performance and mechanism of N1,N1,N3,N3-tetrakis((3,5-dimethyl-1H-pyrazol-1-yl)methyl)propane-1,3-diamine (BF2) and N1,N1,N2,N2-tetrakis((3,5-dime-thyl-1H-pyrazol-1-yl)methyl) benzene-1,2-diamine (BF4) for the corrosion of mild steel in 1.0 M HCl were investigated using weight loss method and electrochemical measurements. The results show that both tetrakis pyrazole derivatives act as good inhibitors, and inhibition efficiency follows the order: BF4 > BF2. Two tetrakis pyrazole derivatives are mixed type inhibitors exhibiting predominantly cathodic behavior. The Nyquist plots showed that, after increasing inhibitors’ concentrations, charge-transfer resistance increased and double-layer capacitance decreased, involving increased inhibition efficiency. The adsorption of both inhibitors on a steel surface obeyed Langmuir model, thus, the thermodynamic and kinetic parameters were calculated and discussed. Quantum chemical parameters are calculated using the Density Functional Theory method (DFT). Correlation between theoretical and experimental results is discussed.

A Ni-Al composite was electrodeposited on a Ni substrate, and its corrosion behavior was observed in 2 M NaCl solution, compared with a pure Ni coating. The Al particles increased the porosity of the composite and encouraged charge percolation, both at the corrosion product layer-solution interface and at the substrate–solution interface, based on EIS characterization. This phenomenon greatly decreased the corrosion potential, and increased both cathodic and anodic current densities in the active region, as well as the passive current density in the passive potential range, during polarization of the composite. Although a continuous Al3+ ions supply to the passivation front was suspected, based on the longer passivation potential of the Ni-Al composite, the simultaneous consumption of the Al products by the chloride ions is the reason for serious cracking and localized collapse of the composite corrosion layer, as confirmed by SEM. This conferred lower corrosion resistance on the Ni–Al composite, compared to the pure Ni coating, in the 2 M NaCl solution.

This work is devoted to examine the effectiveness of pyrazoles 4-(4,5-dihydro-1H-pyrazol-5-yl)-N,N-dimethylaniline (D) on corrosion of mild steel in a 1 M HCl solution, using weight loss measurement at concentration effects. The inhibitor (D) was synthesized in our laboratory. The formation of this pyrazole was carried out with hydrazine and α-unsaturated aldehydes, and the structure was checked by spectroscopic means, such as FT-IR, 1H NMR and 13C NMR. Polarization curves and electrochemical impedance spectroscopy (EIS) methods were used to assess both the corrosion rate and inhibition efficiency. Potentiodynamic polarization showed that D behaved as a mixed-type inhibitor. The Nyquist plots showed that, while D concentrations increased, charge-transfer resistance increased and double-layer capacitance decreased, involving increased inhibition efficiency. Adsorption of the inhibitor molecules corresponds to Langmuir adsorption isotherm. Quantum chemical calculations showed that the inhibitor was prone to be protonated in the acid, and the results were in full agreement with experimental observations.

The degradation of the AB1 dye by electro-generated species using a BDD electrode was performed. The results were explained by the generation of OH* radical, S2O82− in the presence of sulfate, and active halide species in the presence of halide salt. The discoloration rate increases in this order: sulfate, KCl, KBr. In the presence of KCl, the discoloration is affected by the current density, initial pH, temperature, and concentration of the supporting electrolyte; however, the concentration of the dye and the ionic strength showed a negligible effect. The intermediates produced during the discoloration are a function of the pH of the solution. In the presence of sulfate, the discoloration rate is very slow, and the mechanism of discoloration is different from that in the presence of KCl. The thermodynamic parameters of the discoloration are calculated.

This work has investigated the effect of addition of the Be alkaline earth metal on the dissolution behaviour of the Al-Zn alloy anode. Corrosion experiments were mounted to determine the optimal effect of an alkaline earth metal on the efficiencies of the aluminium alloy anodes. The corroded and unexposed sample surfaces were subject to microstructural characterization by using scanning electron microscopy and X-ray diffraction techniques. Al-Zn alloy doped with 1-5% by weight of beryllium was prepared to determine the effect on the anode efficiency in chloride environment. The different microstructure of the evolved Al-Zn alloy was correlated with the anode efficiencies. The obtained results showed that the anode efficiency of the Al-Zn alloy increased with the beryllium incorporation concentration. Al-Zn-Be-3% exhibits the better performance in terms of anode efficiency. The microstructure of the Al-Zn-Be alloy revealed increased distribution of beryllium globules and a breakdown of passive alumina film network on the anode surfaces, thus improving the anode efficiency.

The electrochemical behavior of catechol in the presence of sulfanilic acid has been examined in aqueous solution with numerous pH values, different electrodes and different concentration of sulfanilic acid, using cyclic voltammetry, controlled potential coulometry and differential pulse voltammetry. The reaction of o-benzoquinone with sulfanilic acid in the second scan of potential was observed. It is assumed that the reaction occurred between the sulfonate group of sulfanilic acid and quinone, rather than between the amino group of sulfanilic acid and quinone. The products derived from the reaction are associated with electrons transfer at more negative potentials than those from catechols. The significance of catechol’s pH in presence of sulfanilic acid was studied by varying pH from 2 to 9. The concentration influence of sulfanilic acid with the fixed concentration of catechol (2 mM) was determined from 2 mM to 12 mM. The reaction was toughly affected by the pH, as well as by the concentration of sulfanilic acid. The reaction was mostly promising in 2 mM of sulfanilic acid and 2 mM of catechol at pH 7.

The effect of the concentration and nature of novel 3-hydroxy-3-(4-chlorophenyl-1-(4-sulphonato (sodium salt)) phenyl triazene (HCST) on corrosion and dezinfication of 70/30 brass in 0.5 M HNO3 solution has been investigated by weight loss method. Inhibition efficiency of this corrosion inhibitor was also evaluated at different temperatures ranging from 303 K-333 K. It was observed that HCST showed 88.13% inhibition efficiency at 303 K up to 0.005 M concentration of inhibitor. Weight loss method has been used to analyze the corrosion behavior of the brass in the absence and presence of different concentrations of inhibitor. The corrosion inhibition efficiency increases with increasing concentration of inhibitor and decreases with rise in temperatures. Activation energy (Ea), enthalpy (∆H), entropy (∆S) and Gibbs free energy (∆G) for corrosion process have also been calculated. The adsorption behavior of HCST on brass surface has been found to obey Langmuir adsorption isotherm. Results reveal that hydroxytriazenes can be potential corrosion inhibitors.

The aim of this study was to produce thin films of ternary cobalt-nickel-iron (Co-Ni-Fe) alloy by electrochemical deposition method at different electrodeposition potentials in a sulfate solution (0.15 M CoSO4 + 0.2 M NiSO4 + 0.005 M FeSO4). The Co-Ni-Fe alloy thin films were electrodeposited on indium-doped tin oxide (ITO) coated on a conducting glass substrate. Voltammetric studies indicated the potential range between -1.10 to -1.30 V (SCE) for successful deposition of Co, Ni and Fe. The energy dispersive X-ray (EDX) analysis indicated that the films exhibited anomalous behavior with Ni content significantly increased, whereas the Co and Fe content decreased as the electrodeposition potentials reached more negative values. The scanning electron microscopy (SEM) study showed that the electrodeposited films were uniform for all applied potential values and larger particles were formed when higher electrodeposition potentials were applied. Investigation by X-ray diffraction (XRD) revealed that the dominant phase in the deposited film was amorphous Co-Ni-Fe. Hysteresis curves of the ternary alloy film obtained from vibrating sample magnetometer results prove that the alloy is ferromagnetic. The coercivity mechanism of the Co-Ni-Fe films has obeyed Neel’s relation which is thickness dependence.

The environmental friendly inhibitor system L-cysteine-Zn2+ has been investigated by weight loss method. A synergistic effect exists between L-cysteine and Zn2+ system. The formulation consisting of 250 ppm of L-cysteine and 50 ppm of Zn2+ offers an excellent inhibition efficiency of 99%. Polarization study reveals that this formulation functions as anodic inhibitor. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra study leads to the conclusion that the Fe2+- L-cysteine complex formed on the anodic sites of the metal surface controlled the anodic reaction, and Zn(OH)2 formed on the cathodic sites of the metal surface controlled the cathodic reaction. A suitable mechanism of corrosion inhibition is proposed based on the results obtained from weight loss study and surface analysis technique. Synergism parameters have been calculated. They are found to be greater than 1, suggesting that a synergistic effect exists between L-cysteine and Zn2+.

Annatto extract (dye) was investigated as a cheap and ecologically friendly alternative corrosion inhibitor. The corrosion process was monitored with mild steel coupons in 1.0 M hydrochloric acid at temperatures between 30 oC to 90 oC by weight loss and spectroscopic techniques. The dye effectively inhibited the corrosion of mild steel in the acid at the studied temperatures. Inhibition efficiency obtained was found to vary with temperature and concentration of the dye. Adsorption models were used to predict the nature of the dye-steel surface interaction. Thermodynamic models provided evidence of spontaneous physical and chemical adsorption mechanism with the evolution of heat. Kinetic studies revealed a deepening effect on the activation potential in the presence of the dye. The effect of solvent and synergistic intensifiers on the effectiveness of the dye was also assessed. Heavy metal ion composition in the formulation was determined and was within the limit of environmental and health safety.

N-pyridinium salt derivatives (1), (2), (3), (4) and (5) were prepared and their inhibition effect as corrosion inhibitors for mild steel was investigated in 1 M H2SO4 solution at 30 oC for 24 hs. The corrosion inhibiting action was studied using weight loss measurements. The results have revealed that the corrosion rate decreases, inhibition efficiencies increase and surface coverage degree increases with a higher inhibitor’s concentration. Inhibition efficiencies for prepared N-pyridinium salt derivatives have the highest inhibiting efficiency even for a low concentration. The values of Goads are showing physisorption effect for all prepared compounds. Molecular modeling systems were achieved for the suggested inhibitors (1), (2), (3), (4) and (5). Theoretical calculations could be used as a useful tool to obtain information for explaining the mechanism and nature of interaction between the metal surface and the organic molecule as a corrosion inhibitor.

The peculiarities of the metallographic structure of electrodeposited nanocomposite polymeric modified Zn and Zn-Co (1 wt.%) alloy coatings are described and discussed. These coatings are obtained from usual electrochemical baths for Zn and Zn-Co alloys, but with the addition of stabilized polymeric micelles (SPM). The latter are of core-shell type, and are based on polypropylene oxide (hydrophobic core) and polyethylene oxide (hydrophilic shell). These coatings and their polymeric modified nano-composites are investigated with X-ray (XRD) method, which reveals changes in the metallographic structure as a result of the presence or absence of organic additives (wetting agent and brightener) and SPMs. The possible reasons for the changes observed are commented. In addition, cyclic voltammetry method (CVA) is applied in order to clarify the influence of the applied additives and of SPM on the cathodic (deposition) and anodic (dissolution) processes.

The corrosion inhibition and adsorption of ethanol extracts of Psidium guajava seeds (EEPgS), for aluminum in 0.5 N HCl solutions, were investigated using conventional weight loss, FTIR spectroscopy and SEM analysis techniques. The results showed that EEPgS performed well as inhibitor for the corrosion of aluminum in hydrochloric acid media. FTIR results showed that the inhibition mechanism was by adsorption process, through the functional groups present in the extract. Inhibition efficiency increased with increasing concentration of the plant extract, but decreased with the temperature rise. The weight loss data were fitted into a number of isotherms, though Langmuir model was found to be the best fit. The SEM photographs confirmed the protection offered by the extract on the surface of the metal.

The effect of the addition of phosphoric acid ((HO)3P=O), potassium hydrogen phosphate ((HO)2P(O)(O-K+)), dimethyl vinylphosphonate (CH2=CH―P(O)(OCH3)2) and vinylphosphonic acid (CH2=CHP(O)(OH)2) on lead corrosion in 4 M H2SO4 was studied by potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The results show that phosphoric acid and potassium hydrogen phosphate, added to an optimal concentration of 0.4 M, reduce the lead passivation current and increase its corrosion current, with charge transfer as the main reaction mechanism at the interface metal/electrolyte. They also increase PbO2 formation’s potential when they are added at larger concentrations, while adding dimethyl vinylphosphonate and vinylphosphonic acid up to 0.3 M reduces corrosion current and lead passivation current. This last product appears to suppress the formation of PbO2. The parameters of potentiodynamic polarization are in good agreement with those of EIS.

The corrosion behavior of aluminium in 1 M NaOH solution, in the absence and presence of some aromatic carboxylic acids, was investigated using potentiodynamic polarization techniques, electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). The results among the investigated aromatic carboxylic acids, 4 bromomethyl, 3 bromo and 3-hydroxy benzoic acid were more efficient corrosion inhibitors for aluminium in alkaline medium. The values of different thermodynamic parameters such as adsorption equilibrium constant (Kads) and free energy of adsorption (ΔGads) were calculated and discussed. The adsorption process of studied inhibitors on aluminium surface obeys the Langmuir adsorption isotherm.