Portugaliae
Electrochimica Acta

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.

Cefixime was investigated as a corrosion inhibitor for mild steel in an hydrochloric acid solution. The results revealed that the order of reaction is 0.427, with activation energy found to be 41.7 kJ/mol. Cefixime was effective in increasing the inhibition efficiency for all inhibition concentrations. The corrosion rate profile was found to be second-order kinetics with respect to corrosion activity.

Corrosion of steel pipes, tubing, and casings in the oilfield by acidizing fluids is a major cause of materials failure. Corrosion of X80 steel in hydrochloric acid, a typical acidizing solution, was probed using gravimetric and electrochemical techniques. Fluvoxamine (FLU) was used as anticorrosive additive to the acid, and monitored between 30 oC to 90 oC. FLU offered efficient protection for the X80 steel by inhibition. The inhibitive effect increased with a higher FLU concentration, but decreased as temperature increased. The highest concentration of FLU (10x10-5 M) afforded inhibition efficiency of 93.5% and 80.4% in 1 M and 15% HCl, respectively, at 30 oC. The efficiency decreased to 88.5% and 73.3%, respectively, at 90 oC. Inhibition efficiency was improved by blending FLU with glutathione, polyethyleneglycol and potassium iodide. Adsorption and thermodynamic studies reveal that the inhibitor functions, by spontaneous exothermic adsorption on X80 surface, were best described by Langmuir adsorption model. Impedance measurement reveals increase in charge transfer resistance with decrease in double layer capacitance. Polarization studies show that FLU acts as a mixed type inhibitor. Scanned micrographs of X80 surface show a lower pitting in the presence of FLU than in the free acid, demonstrating the effectiveness of FLU as X80 steel corrosion inhibitor.

Measurements of the electric current as a function of time during the electrochemical deposition of metals are usually treated considering models based on the Kolmogorov-Avrami theory or alternatives to it including hierarchical overlap of diffusion zones. These models explain the main tendencies of the nucleation and growth of the metallic deposits but still do not include details related to the anomalous deposition of metallic alloys, although the electrochemical methods are widely used for their production. In this work, a discussion of the several factors involved in this issue is presented to evidence the need for a more comprehensive model that may reach a complete quantitative description of electrodeposition of alloys including the anomalous phenomenon. Cyclic voltammetry as well as chronoamperometry measurements in a sulfate solution for Ni-Fe deposition were used to exemplify several aspects to be better understood and included in the model. Some Ni-Fe films were also deposited and characterized by scanning electron microscopy and ferromagnetic resonance to discuss some additional aspects as final composition and structure.

A minimal instrumentation micropolarograph was built, and its metrological characterization was performed. The oxidation of K4[Fe(CN)6] was studied by linear voltammetry. A microdisc and a bar of carbon were used as working and auxiliary electrodes, respectively. A bar divided into compartments of copper-internal solution-cotton was used as reference. The linear coefficient of determination between the limiting current and the concentration was 0.9926, in the range of 10-2 - 10-1 mol L-1. The coefficient of variation of ten voltammograms at 0.08 mol L-1 was 1.8 %, being inferior to the maximum value reported for these methods. Mood and Kruskal-Wallis tests did not show significant differences between voltammograms. In the range of linear correlation coefficients of potential sweep 0.9488 to 0.9989, no sweep influence on voltammograms was observed. The expanded uncertainty associated with the determination of the limiting current was 1.9 µA. The linear voltammograms for oxidation of ascorbic acid and KI were obtained, showing correspondence with the reported results.

Green is attractive and beautiful. Green chemistry has attracted scientists and researchers from various fields. Electrolysis is considered as green electrochemistry, because electrochemical process can be stopped and controlled at any time and at any stage of the reaction. Usually water is used as the solvent. Corrosive acids are not used. Toxic chemicals are not involved. The main components of an electrolysis process are anode, cathode and electrolyte. By using suitable anodes, cathodes and medium, electrolysis has been applied in various fields. Electrolysis has been used to decolourise dyes from effluents of textile industries. The decolourisation efficiencies of various anodes, such as platinised-titanium, mild steel and aluminium in various electrolytic media, such as well water and sea water, have been evaluated and compared. The role of positive chlorine in the decolourisation process has been established. Electrolysis, in presence of a suitable reducing agent, has also been used to synthesize nanoparticles. Copper nanoparticles and silver nanoparticles have been produced by making use of reducing agents, such as sodium potassium tartrate and trisodium citrate. Various plants extracts have also been used as reducing agents. The nanoparticles synthesized by green methods have been characterized by UV-Visible absorption spectroscopy and fluorescence spectroscopy. The surface morphology of these nanoparticles has been characterized by SEM and EDS. Blue pigment that can be used in paint industry has been synthesized by green electrolysis. For this purpose, waste mild steel rod has been used, and graphite has been used as anode. The blue pigment prepared has been characterized by UV-Visible absorption spectroscopy and fluorescence spectroscopy. The surface morphology of these nanoparticles has been characterized by SEM and EDS. The blue pigment prepared is found to be in the nano range. This can be used in paint industry and also in the field of nano biosensors. By green electrolysis method, Hofmann rearrangement has been successfully effected, benzamide being the starting material. The product obtained has been diazotised and coupled with α-napthol and β-napthol to give dyes. The dyes have been characterized by UV-Visible absorption spectroscopy and fluorescence spectroscopy. Polyaniline has also been synthesized by green electrolysis process, without using expensive oxidizing agents, but using positive chloride ions generated in-situ during electrolysis, in the presence of sodium chloride solution as electrolyte. The polyaniline produced has been characterized by UV-Visible absorption spectroscopy, fluorescence spectroscopy and FTIR spectra.

Febuxostat FEB was determined by differential pulse “DP” adsorptive stripping voltammetry and hanging mercury drop electrode. In 0.04 mol L-1 Britton-Robinson buffer solution, pH 10, an irreversible electrochemical reaction took place at about -350 mV, and the peak current was linearly varied over the concentration range of 12.5-200 ng mL-1 FEB, with correlation coefficients of 0.9995, after 60 s accumulation time, stirring at a speed of 600 rpm, rest for 10 s, then cathodic stripping sweep from -100 to -600 mV, with a scan rate of 60 mV/s. The limits of detection and quantization were 6.93, 23.09 ng mL-1. The method was applicable for determining FEB in pharmaceutical tablets and in spiked plasma. The results of the proposed method were compared with that obtained by the UV-spectrophotometric technique.

UNS G10150 steel was electrodeposited with Zn-30Al-7%Ti, in the presence of solanum tuberosum, under sulphate condition, via dual anode route. The microstructures of the deposited layers were examined using scanning electron microscopy (SEM), atomic force microscope and X-ray diffractometry (XRD). The microhardness properties and wear characteristics were performed using a diamond based microhardness tester and a CERT reciprocating sliding tester. The microstructure revealed a massive structural transformation with hexagonal dendritic and whisker-like structure for the Zn-30Al-7%Ti coating. There was a significant rise in surface micro hardness values of the co-deposited layers, due to the presence of hard phase TiO2 particles, and solanum precipitation. The surface strengthening effect induced by solanum, and Al/TiO2 addition, with the presence of Zn2Al3Ti2, could be responsible for low plastic deformation and improved hardness of the coating. It is established that the electrodeposition route via dual anode of Zn-Al-Ti with adsorbed fluid on UNS G10150 steel can be used to improve the surface hardness values, aesthetic properties and wear resistance.

The present work aims to investigate and correlate the wear behavior of electroless Ni-P-W coating under dry and lubricated conditions with the tribological testing parameters. A pin - on - disc configuration test setup is used for the same. Taguchi’s orthogonal design of experiments technique is used to carry out the experiments. Both response surface and fuzzy rule based models are seen to be effective in determining the complex interrelationship between the wear depth of the coatings and the test parameters, namely applied normal load, sliding speed and sliding duration. The coefficient of determination for fuzzy logic based predictions is seen to be higher than the regression predicted ones, indicating better modeling capabilities of the artificial intelligence technique. ANOVA results reveal that the wear depth is mostly influenced by sliding speed followed by applied normal load and sliding duration for both dry and lubricated conditions. Coating composition, phase transformation and microstructure studies are undertaken to analyze their effects on the wear behavior. Abrasive wear mechanism is seen to be the predominating under both dry and lubricated condition. The coatings are seen to suffer more wear under dry sliding condition compared to lubricated environment.

Anodic electro catalysts are developed by using a titanium substrate coated with different compositions of mixed oxides, as it follows: ruthenium-titanium mixed oxides; ruthenium-titanium-tin mixed oxides; and ruthenium-titanium-iridium mixed oxides. The performance of electro catalysts was further evaluated by measuring coating thickness, studying coating morphology with microscope, identifying the presence of RuO2, TiO2, IrO2 and SnO2 in coating film, analyzing shape of individual crystal by XRD, performing accelerated life test and current efficiency test of the selected anode. The coating composition of 15% RuO2, 15% IrO2 and 70% TiO2 exhibited premium properties among the studied anodes.