Portugaliae
Electrochimica Acta

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.

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.