Portugaliae
Electrochimica Acta

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.

Enhancement of corrosion inhibition of copper by polyvinylpyrrolidone (PVP) upon application of a square wave potential regime to copper specimens was investigated. The results indicated a marked decrease of copper corrosion rate upon application of a square wave to copper specimens in PVP – containing solutions. The inhibition enhancement was found to increase when increasing PVP concentration, and with a larger time of exposure with application of the square wave potential regime. A 500 Hz frequency was the optimal frequency for promotion of inhibition by PVP. SEM micrographs revealed that application of the square wave converted the dendritic coverage of PVP to a more uniform layer of PVP at copper surface. The enhancement of corrosion inhibition by application of the square wave might be explained on basis of the enhanced adsorption of PVP onto copper surface by application of the square wave potential regime. Application of square wave potential regime apparently influences the PVP adsorption coverage at the copper surface.

This project assessed the technical feasibility of organic matter (COD) removal in livestock effluents, by electrocoagulation. An experimental design was used to block two factors at three levels, to evaluate the effect of the variables distance between electrodes and pH, using aluminum sacrificial electrodes. Maximum removal (90.16%) was obtained at 7 units pH, and 2.0 cm distance between electrodes. This study demonstrated the technical feasibility of electrocoagulation (EC) for the removal of organic matter as COD, present in wastewater from the livestock industry.

Modeling the corrosion inhibition of mild steel in HCl medium with inhibitor of pawpaw leaves extract is presented. The extract was analyzed using gas chromatography-mass spectrometry. Thermometric and gravimetric methods were employed in the corrosion inhibition study. The inhibition efficiency was modeled and optimized using response surface methodology (RSM). It was observed that the free energy of adsorption (∆Gads) was negative and less than the threshold value of -40 kJ/mol. The adsorption of the extract was spontaneous, and occurred according to the mechanism of physical adsorption. A quadratic model was generated, with optimum inhibition efficiency of 80.29% obtained. The extract was highly efficient in the corrosion control process. It is effective for surface treatment of mild steel in the acid medium. Therefore, it is recommended that pawpaw leaves extract should be employed as corrosion inhibitor in oil well acidizing and surface treatment of mild steel.

The influence of surface topography and cutting parameters on the corrosion resistance of stainless steel UNS S31600 in a 6% NaCl solution is addressed in the present study. Surface topography has been modified by changing the conditions parameters of superfinish turning, including feed, cutting speed and depth of cut, and their correlations with corrosion resistance have been examined. The results showed that the depth of cut is correlated with the corrosion potential. Moreover, the increase of cutting speed degrades the corrosion resistance and increases the corrosion potential in the anodic phase. In its turn, the polarization resistance increases in a manner correlated with increasing the surface quality.

Use of inhibitor is proven as an efficient and widely accepted corrosion prevention method. Corrosion control of steel is an important activity in technical, economic, environmental and safety terms. This article enumerates several types of inhibitors used to combat corrosion in acidic medium. In this paper, literature on corrosion inhibitors has been reviewed and discussions are made on properties and efficiency of inhibitors. (The prominent features of our work on the mechanism of corrosion inhibitors have been highlighted and in a few cases have tried to predict its mechanism).

The present work has been carried out to study the mechanism of electrochemical degradation of Congo red dye. Electrolysis has been carried out in a single-chamber electrochemical cell having graphite anode and platinum cathode in the presence of KCl as supporting electrolyte under amperostatic conditions. The potential across the electrodes has been adjusted so that a constant 30 mA current passed through the cell. The effect of various operating parameters such as current density, initial dye concentration, nature of supporting electrolyte KCl, pH and electrode materials, on electrochemical degradation of Congo red dye has been investigated. The decolourization efficiency was assessed through UV-Visible studies which are supported by a percentage reduction in Chemical Oxygen Demand (COD). Kinetic studies indicate that decolourization takes place through a second order diffusion controlled reaction. Energy consumption has been calculated. It is observed from Fourier transform infrared spectroscopy (FTIR) and mass spectra that Congo red dye has been degraded to small molecules. Results indicate that electrochemical degradation of Congo red by using low-cost graphite electrodes proves to be an efficient method at an optimum current density of 1.805 mA cm-2.

The inhibition and the effect of temperature and concentration of 1,4-di(1-vinyl-3-methylimidazolium) benzene dibromide (VMIBB) on the corrosion of mild steel in 1.0 M HCl solution was investigated by electrochemical polarization and weight loss experiments at temperatures ranging from 303 to 343 K. The studied inhibitor concentrations ranged between 1.0x10-6 M and 1.0x10-2 M. The percentage inhibition increased with the increase of the inhibitor’s concentration. The percentage inhibition has reached about 93 % at the concentration of 1x10-2 M and 303 K. On the other hand, the percentage inhibition decreased with the increase of temperature. Using the Langmuir adsorption isotherm, the thermodynamic parameters for the adsorption of this inhibitor on the metal surface were calculated. 1,4-di(1-vinyl-3-methylimidazolium) benzene dibromide was found to be a potential corrosion inhibitor, since it contained not only nitrogen, but also three aromatic systems, double bond, and it is a large molecule which has a big surface with high malar surface coverage.

1-(2-Dodecylsulfanyl-ethyl)-1H-imidazole (DSEIm) and 2-Imidazol-1-yl-ethyl-sulfanyl)-acetic acid (ImESAA) were synthesized via radical catalysis method and characterized using 1H NMR and 13C NMR spectroscopy. The corrosion performances of mild steel specimens were studied by three imidazole derivatives include: 1-vinylvinylimidazole (VyIm), DSEIm and ImESAA, which were investigated in 1.0 M HCl using weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopic (EIS) method. The results obtained show that DSEIm is the best corrosion inhibitor; its inhibition efficiency (E %) increases with increasing the inhibitor concentration, but decreases with the raise of temperature. Potentiodynamic polarization studies clearly revealed that the inhibitors changed the mechanism of hydrogen evolution, and that they acted as mixed inhibitors, but most effectively in the cathodic range. The higher values of activation energy (Ea) in the inhibited solution can be correlated with the increased thickness of the double layer; this is interpreted with physical adsorption of the inhibitor onto the metal surface resulting in the formation of a surface film. Adsorption of imidazole derivatives have been studied with Monte Carlo simulations.

Silver chloride modified carbon paste electrode was prepared as a new electrode and used to electrocatalytic oxidation of ethanol. For the first time, the catalytic oxidation of ethanol was demonstrated by cyclic voltammetry, chronoamperometry and amperometry methods at the surface of this modified carbon paste electrode. Compared to silver chloride modified carbon paste electrode, silver bromide modified carbon paste electrode and bare silver electrode catalysts, silver chloride modified carbon paste electrode exhibited markedly superior catalytic activity for the electrocatalytic oxidation of ethanol. It can be seen that the electrocatalytic efficiency of silver chloride modified carbon paste electrode is higher than the silver bromide modified carbon paste and bare silver electrodes. The catalytic oxidation peak current was linearly dependent on the ethanol concentration. The j0 for silver chloride modified carbon paste and silver bromide modified carbon paste electrodes are 11.2 and 5.4 folds respectively higher than that of the bare silver electrode. For silver chloride modified carbon paste electrode, the charge transfer coefficient (α), the number of electrons involved in the rate determining step (nα) and exchange current density (j0) were calculated as 0.46, 1 and 5.05×E–7 respectively. The modified electrode possesses high selectivity, good reproducibility and well stability.

A novel self modification of grafted polymer working electrode with carbon nanotubes was success for fabrication from grafting polymer via gamma irradiation and ferrous ammonium sulfate (FAS) as a catalyst. The electrochemical properties of the self modified grafted polymer with CNT (GPESMCNT) improved performance the working electrode at higher conducting surface was done through using in cyclic voltammetry (CV). The GPESMCNT was characterized by surface analytical methods including AFM and SEM. The characterization of electrocnductivity properties of GPESMCNT was studied in 1M of KCl with different concentration of K3[Fe(CN)6], at different scan rates, temperature, and different concentrations using CV technique. The new GPESMCNT improved performance the working electrode in CV at different techniques such as rotating disc electrode (RDE). also, the nanomaterials in the chain of grafted polymer was enhanced the redox current peaks of Fe(II)/Fe(III) multi times than at commercial working electrodes such as GCE, Pt-electrode, Au-electrode, etc.

Electro polishing is defined as anodic corrosion. The issue of the effects of corrosion on structural integrity of metal surfaces has been a question of concern for some time. The uses of chemical corrosion inhibitors are common in production and processing operations. Nevertheless, the challenge is to develop a new class of corrosion inhibitors to protect the materials, due to the economic importance of copper there are several researches deals with acceleration and inhibition of this process. In this paper the electropolishing process inhibited with different ratio by addition of some organic alcohols (methanol, ethanol,propanol, and isopropanol) by addition with concentration (2, 5, 10, 15, 20, 25 and 30 %) .The results reveal that these organic alcohols have a strongest inhibitive effect ranging from8. 7 – 53.8 % and the thermodynamic parameters were present.

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.