Portugaliae
Electrochimica Acta

The assessment of Psidium guajava leaf extract as corrosion inhibitor for double thermally-aged Al-Si-Mg (SSM-HPDC) alloy in 3.5%wt NaCl solution using the gravimetric and potentiodynamic polarization techniques was investigated. The gravimetric test was carried out at different inhibitor concentration, time and temperature ranges of 0.1-0.5%v/v, 1-5 hrs and 30-70oC. The results revealed that Psidium guajava leaf extract in 3.5%wt NaCl solution-aluminium environment decreased the corrosion rate at various concentrations considered. Inhibition efficiency (IE) of 72.1% at 0.5% v/v Psidium guajava leaf extract addition using the gravimetric method was demonstrated in 3.5%wt NaCl solution. The IE from the potentiodynamic polarization method was significantly enhanced as high as 98.89%/0.5%v/v. The additions of Psidium guajava leaf extract as corrosion inhibitor in the solution indicate higher potential value, IE and polarization resistance with decrease in current density. The methods for assessment of the alloy were in agreement and mixed-type corrosion exist which obeyed the Langmuir adsorption isotherms. The optical microscopy (OPM) revealed that the microstructure of the double thermally-aged sample has finer grains and enhanced grain boundaries compared to the untreated sample. The scanning electron microscope (SEM) surface morphology of as-corroded uninhibited condition showed severe damage and pit formation than as-corroded inhibited.

Cefuroxime axetil (CA) a prodrug was tested as corrosion inhibitor for aluminum in hydrochloric acid solution using thermometric, gasometric weight loss and scanning electron microscope (SEM) techniques. Results obtained showed that this compound has a good inhibiting properties for aluminum corrosion in acidic medium, with inhibition efficiencies values reaching 89.87 % at 0.5 g / L . It was also found out that the results from weight loss method are highly consistent with those obtained by hydrogen evolution method and gasometric method; and all indicate that inhibitor efficiency increases with increasing inhibitor concentration. Cefuroxime axetil inhibited the corrosion of aluminum in solutions of HCl through the mechanism of physiosorption as confirmed by values of activation energy and free energy of adsorption. The adsorption of the inhibitor was also found to be spontaneous, exothermic and best fitted the Langmuir adsorption model. SEM analysis confirmed the existence of an absorbed protective film on the aluminum surface.

The acid corrosion inhibition process of copper in 2 M H3PO4, containing 0.3 M of NaCl by an eco-friendly ionic liquid, 1-pentyl pyridazinium bromide (PPB), has been investigated using weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopy (EIS).The effect of temperature on the corrosion behavior with the addition of PPB was studied in the temperature range 298–328 K. The value of inhibition efficiency decreases slightly with the increase in temperature. Results show that PPB is a good inhibitor and inhibition efficiency reaches 91 % at 10-3 M. Gravimetric essays indicate that PPB inhibits the corrosion of copper and the value of inhibition efficiency reaches 90 % at 10-3 M of the inhibitor. Potentiodynamic polarization curves showed that the PPB affects both cathodic and anodic current and may be classified as a mixed type inhibitor in (2 M H3PO4 + 0.3 M NaCl). For the inhibitor, the inhibition efficiency increased with an increase in the concentration. The adsorption of this compound on copper surface obeys Langmuir’s adsorption isotherm. To elaborate the mechanism of corrosion inhibition, the kinetic and thermodynamic parameters for copper corrosion and inhibitor adsorption, respectively, were determined and discussed. Inhibition efficiency values obtained from weight loss, polarization curves and EIS are reasonably in good agreement. Theoretical calculations provide good support to experimental results.

In this paper, an efficient artificial neural network (ANN) model using multi-layer perceptron (MLP) philosophy has been proposed to predict the fireside corrosion rate of super heater tubes in coal fire boiler assembly, using operational data of an Indian typical thermal power plant. The input parameters comprise coal chemistry, namely, coal ash and sulfur contents, flue gas temperature, SOX concentrations in flue gas, fly ash chemistry (wt% Na2O and K2O). An efficient gradient based network training algorithm has been employed to minimize the network training errors. Effects of coal ash and sulfur contents, wt% of Na2O and K2O in fly ash and operating variables such as flue gas temperature and percentage excess air intake for coal combustion on the fireside corrosion behavior of super heater boiler tubes have been computationally investigated and parametric sensitivity analysis has been undertaken. It has been observed that ash and sulfur contents of coal, flue gas temperature and fly ash chemistry have a relatively predominant influence on the rate of fireside corrosion with respect to other parameters. Quite good agreement between ANN model predictions and the measured values of fireside corrosion rate has been observed, which is corroborated by the regression fit between these values.

The corrosion inhibition efficiency of Capparis spinosa (CS) extract on the corrosion of copper in a 1.0 M NaOH solution was investigated using weight-loss, polarization and potentiodynamic corrosion rate measurements. The weight-loss showed that the inhibition efficiency of CS extract increased when increasing concentrations of CS extract and the immersion time. Maximum inhibition efficiency was 85%, which was obtained at 440 ppm of the CS extract at 45 °C in 1.0 M NaOH. Polarization measurements showed that the CS extract acts as a mixed type inhibitor. The cyclic voltammetry and potentiodynamics measurements suggested that the adsorbability of CS extract on copper was a bulk process, since surface coverage increased when increasing the concentration of CS extract. Thermodynamic measurements showed that the adsorption of CS extract on copper was physical, spontaneous, and favored at high temperatures. The adsorption of the inhibitor on a copper surface was in accordance with the Langmuir adsorption isotherm.

The corrosion inhibition characteristics of essential oil of mentha pulegium leaves have been studied as a green inhibitor of corrosion of aluminum in 2 M phosphoric acid using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS). The effect of inhibitor concentration shows that efficiency increases with increase of concentration with maximum of 79% at 1800 ppm. Polarization curves reveal that the essential oil of mentha pulegium leaves acts as a cathodic inhibitor. The effect of temperature on aluminum corrosion behavior was also studied and thermodynamic data of activation was determined.

Since its inception, the utilization of electroless nickel coatings in industries has increased by leaps and bounds, due to their excellent mechanical/electrical properties, hardness, high corrosion and wear resistance and low coefficient of friction. Their behavior in lubricated environments is an interesting subject of research and needs more attention. In the present study, the wear behavior of electroless Ni-P coating under lubricated condition has been investigated. Electroless Ni-P coating has been deposited on mild steel substrate. Characterization of the deposited Ni-P coating has been done using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyzer and X-ray diffraction (XRD) technique. A prediction model for the wear depth of the deposits with varying normal load, sliding speed and sliding time has been developed using multiple regression analysis and fuzzy logic, which is a very efficient artificial intelligence technique for modeling and monitoring systems. Experiments are carried out according to Taguchi’s L27 orthogonal array of experiments. The results obtained from the prediction models are seen to be in good agreement with experimental results. The applied normal load and sliding time are found to have a significant influence on the wear of electroless Ni-P coating. The wear mechanism was found to be mild abrasive in nature.

Communication by Prof. Dr. João Evangelista Simão when receiving the SPE Award for his outstanding scientific career and for his contribution to the Portuguese Electrochemical Society at the XIX Meeting of the Portuguese Electrochemical Society and XVI Iberic Meeting of Electrochemistry. (In Portuguese)

Cobalt complex with flutamide was synthesized and physico-chemically characterized by amperometry, polarography, elemental analysis and IR spectrometry. After synthesizing the metal complex, it was evaluated for antibacterial and antifungal activities against various pathogenic microorganisms such as Streptococcus aureus, Prosteus mirabilis, Klebsiella pneumonia and Aspergillus niger, Nigrosporan sp Fungi. B16-F10 melanoma cell and C-57BL/6 mice have been used for anticancer screening of the metal complex for in vitro and in vivo study. The result of pharmacological studies with M:L revealed that the complex is more potent as compared to the pure drug as regards to its anticancer activity.

Pt nanoparticle-multi walled carbon nanotubes nanocomposites supported on titanium substrate (Pt-MWCNTs/Ti) were prepared by co-electrodeposition method. This composite catalyst was characterized by scanning electron microscopy (SEM), energy dispersive spectrum (EDS), and electrochemical methods. The SEM images reveal that nanostructures are distributed at the surface of the titanium plate. Electro-oxidation of methanol was investigated in acidic media on Pt-MWCNTs/Ti electrodes via cyclic voltammetric analysis in the mixed 0.1 M methanol and 0.1 M H2SO4 solutions. The Pt-MWCNTs/Ti catalyst has good electro-catalytic activity for methanol oxidation. This novel Pt-MWCNTs/Ti catalyst can be used repeatedly and exhibits stable electro-catalytic activity for the methanol oxidation.

The present work describes the preparation and characterization of polyvinyl chloride membrane doped with methyl-salin ionophore. This electrode was successfully used for selectivity and high sensibility of monohydroxiphosphate in aqueous solution. 1 µM detection limit of mono-hydrogen phosphate was obtained by using dibutyl phthalate and o-nitrophenyl octyl ether-poly vinyl chloride membrane in dynamic solution. The co-existence of a large excess of salts did not interfere with the detection in case of o-nitrophenyl octyl ether-poly vinyl chloride membrane that maked this selective electrode more adequate for the monohydrogen detection. Also, a highly selective and sensitive dihydrogen phosphate sensor was fabricated by autoassembly of polyvinyl chloride into silicium nitride gate of ISFET.

Susceptibility of mild steel to corrosion attack has restricted its industrial applications, despite its numerous advantageous characteristics. Comparison of the inhibitive tendency of a mixture of zinc gluconate (ZG) and ferrous gluconate (FG) on the corrosion behavior of mild steel in acid and saline media was investigated using electrochemical and weight loss techniques. The FG:ZG ratio was dosed from 0.5:0.5 to 2.0:2.0 g/v at an interval of 0.5:0.5. The surface morphology of the corroded mild steel samples was evaluated by high resolution scanning electron microscope equipped with energy dispersive spectroscopy (HR-SEM/EDS). Experimental results indicated that the combined inhibitor significantly reduced the corrosion rates of mild steel, with the maximum inhibition efficiency (IE) of 100% and 48% at 28 ºC in the presence of 1.5:1.5 g/v concentrations in 3.5 % NaCl and 0.5 M H2SO4 solutions, respectively. The SEM micrographs of the inhibited samples show a clearly reduced surface degradation as opposed to the surface morphology without inhibitor. Potentiodynamic polarization curves studies showed that the combined inhibitor is a mixed type inhibitor for mild steel corrosion in 3.5 % sodium chloride and 0.5 molar sulphuric acid solutions. From the set of experimental data it was found that the combined inhibitor reduced the corrosion rate through an adsorption process and obeyed Langmuir’s adsorption isotherm in chloride medium and Freundlich adsorption isotherm in sulphuric acid medium at all concentrations and temperature studied. Good synergism exists between FG and ZG. The results obtained from potentiodynamic polarization are consistent with the results of the weight loss method. Synergistic performance of inhibitors was perfect in saline medium. From the analysis of grey relational grade model, the significant concentration ratios were indentified. The results showed the influence of synergistic FG:ZG at a concentration of 1.5 g/v on the corrosion rate of mild steel. Predicted results were found to be in good agreement with experimental results.

This paper aims at investigating the influence of process parameters on micro hardness of metal matrix / material particle coated steel plates. The electro deposition parameters such as current density, pH of bath, bath temperature, Al particles concentration in the bath and agitation speed were considered for this study. Nickel matrix / aluminum particle composite coatings were prepared from a Watt’s bath by electro-codeposition method. The Taguchi method was used to establish the relationship between the process parameter and response variable, micro hardness of the coated plate. L27 Taguchi orthogonal design was employed for conducting the experiments. The micro-hardness of the deposits was examined using a Vickers micro-hardness tester with the payload of 100 g for 10 sec of indentation period. Signal-to-noise ratio and analysis of variance were employed to determine the significance of the process parameter. The surface morphologies of coating and vol. % of Al particles in deposits were analyzed using optical and scanning electron microscope observations.

Corrosion behavior of aluminum in 0.1 M HCl, 0.1 M HClO4 and 0.05 M H2SO4 solutions was studied using potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. The results showed that the rate of corrosion of aluminum was arranged in the order: HCl > HClO4 > H2SO4. Lupine extract is an effective green inhibitor for the corrosion of aluminum in acidic solutions. The inhibition efficiency of the extract was found to increase with increasing the concentration of the extract. The obtained results showed that the lupine extract is effective in the order HClO4 > HCl > H2SO4. Theoretical fitting of the corrosion data to the Kinetic-thermodynamic model was tested to clarify the nature of adsorption.

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.