Portugaliae
Electrochimica Acta

The inhibitory activity of ethanol extract of Nerium oleander leaf (NOLE) on carbon steel corrosion in 0.5 M and 1.0 M of hydrochloric acid solutions was studied by weight loss method and electrochemical techniques. The inhibition efficiency (w) increased with an increase in the concentration of NOLE and in temperature. Polarisation curves indicated that NOLE acts as a mixed type of inhibitor. The changes in charge transfer resistance (Rt) with increasing inhibitor (i.e. NOLE) concentration assured the adsorption of the inhibitor onto the metal surface. The results of w, p (inhibition efficiency obtained from polarisation study) and R (inhibition efficiency obtained from impedance analysis) are in par with each other. Surface morphology study uncovered the coating of the inhibitor molecule on the metal surface. The phenomenon of physical adsorption has been established based on the inhibition efficiency of the inhibitor with change in temperature.

In cooling water systems, seawater can be used. L 80 can be used as a pipeline for carrying sea water. However, this alloy will undergo corrosion. Corrosion can be prevented by the addition of inhibitors such as sodium potassium tartrate (SPT), trisodium citrate (TSC) and zinc sulphate. Corrosion resistance of L 80 alloy in sea water, in the absence and presence of the above inhibitors, has been evaluated by polarization study and AC impedance spectra. It was observed that SPT and TSC show better inhibition efficiency in the presence of Zn 2+. Further, it was found that the SPT-Zn system is better than the TSC-Zn system.

The corrosion inhibition efficiency of a new benzimidazole derivative, namely, 1-decyl-2-[(5-methylisoxazol-2-yl)methyl]benzimidazole (DIB) for carbon steel in 1 M hydrochloric acid (HCl) was studied by EIS and PDP electrochemical methods. The results indicate that DIB reduces carbon steel corrosion rate in the corrosive medium, and its inhibition efficiency increased with the concentrations. The polarization data indicate that DIB is of a mixed type. EIS study reveals that DIB is adsorbed onto the corroding metal surface, creating a barrier between the acid and carbon steel. The DIB molecules adsorption fitted into Langmuir adsorption isotherm. Furthermore, DIB electronic properties that correlate to its corrosion inhibitory such as EHOMO, ELUMO, energy gap (∆E), dipole moment (µ), electronegativity (), global hardness () and the fraction of electrons transferred from DIB molecule to the metallic atom (∆N), were calculated in PCM solvent at the B3LYP/6-311+G (d, p) level of theory. The theoretical results are in good agreement with the observed corrosion inhibition efficiency of the tilted compound.

The electro-oxidation of 4-amino-3-methyl-1,2,4-triazole-5-thione (MTSNH) on a bronze substrate in an alkaline methanol solution produces a homogeneous polymer film. The formation kinetics of the film was investigated using cyclic voltammetry, chronoamperommetry and electrochemical impedance spectroscopy. Cyclic voltammograms indicated that the polymer film (pMTSNH) was formed anodically between -350 and 350 mV/SCE. During the second cycle, the oxidation peak of the monomer disappeared, indicating the formation of the insulating film. We have also shown that the monomer oxidation reaction is essentially irreversible and controlled by a diffusion process. The inhibition efficiency of this polymer was determined by potentiodynamic polarization and electrochemical impedance spectroscopy in a 3.5% NaCl solution.

The inhibition performance of twenty-five amino acids and related compounds was studied by theoretical techniques. The effect of the acidic solution was considered on the molecular dynamics simulation, and the calculated binding energies for most of the inhibitors was ˃100 kcal mol−1, suggesting chemisorptive interactions. Density Functional Theory (B3LYP/6-31G*) quantum substance chemical study was utilized to discover the upgraded geometry of the inhibitors. Also, a linear quantitative structure-activity relationship (QSAR) model was built by Genetic Function Approximation (GFA) method, to run the regression analysis and build up connections between various descriptors and the experimental inhibition efficiencies. The prediction of corrosion efficiencies of these inhibitors nicely matched the experimental measurements. The statistical parameters are: 0.973421, which indicates that the model was excellent. The proposed model has great dependability, strength, and consistency on checking, with inward and outside approval.

In this paper, we report on the preparation of an amorphous and nanocrystalline structure of titanium dioxide, by cathodic electrodeposition on fluorine doped tin dioxide (FTO) coated glass, from an aqueous peroxo-titanium complex solution. Structural X-ray analysis shows anatase phase for heated deposits, and an amorphous form for non-heated deposits. Scanning electron microscopy (SEM) allowed investigating the morphological aspect of the deposits which exhibited nano-particulate grain size. AFM results exhibited the different roughness values of both kinds of films. The crystalline deposits have been used as catalysts for the photocatalytic oxidation of methyl orange dye, under an irradiation source (UV lamp of 365 nm). The results revealed that the dye has undergone a slight degradation under UV illumination. Using spectrophotometer measurements, the decolourisation rate was estimated from residual concentration.

Certain N, O, S-ligating ring compounds and thioureas were investigated to understand their role of copper corrosion inhibition in acetonitrile. For 5 quinones under study, including xanthone, xanthene, thioxanthone, acridone and 1,4-naphthoquinone, acridone was the best inhibitor, with Cu corrosion rate of 4.495 × 10-4 mm/year, whereas 1,4-naphthoquinone exhibited the lowest inhibition, due to a lower number of nitrogen groups. With the presence of sulphur, to form a stronger bond with Cu, thioureas had better inhibiting behavior than quinones. Of 4 thioureas, namely thiourea (tu), diphenylthiourea (dptu), phenylthiourea (ptu), and ethylenethiourea (etu), the fourth shows the highest inhibition – with Cu corrosion rate of 2.27 × 10-4 mm/year – and the third shows the lowest one, due to the steric effect from the phenyl group. When halide ions are present, the inhibition efficiency of thioureas decreases, due to more preferable Cu complexation to halides; the strongest copper-halide bond formation occurred by the freest iodide ion, which is consistent with the results from X-ray crystallography and electrochemistry.

Natural oil extracted from apricot seeds was evaluated as carbon steel corrosion inhibitor in 1 M hydrochloric acid, using potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and weight loss measurements. The measurements show that apricot seed oil is a good inhibitor for carbon steel corrosion in a hydrochloric environment, and this inhibitive action was mainly due to its adsorption onto the carbon steel surface, and active sites blocking. The above results showed that apricot seed oil acted as a mixed-type corrosion inhibitor, and that its adsorption onto the carbon steel surface obeyed the Langmuir adsorption isotherm. The inhibition effectiveness increased with the inhibitor concentration, and reached 83.49% at 0.5 g/L, in a 1 M HCl medium. Some thermodynamic parameters of the studied inhibitor were calculated and discussed.

Surface laser treatments of commercially pure titanium plates (CP-Ti grade 4) were performed in air using a Nd:YAG laser source of short pulse duration about 5 ns. Attention is drawn to the following laser-processing parameters: laser-power interaction time and surface of the irradiated zone. The morphology, structure and chemical composition of the formed layers were analyzed by different characterization techniques providing physico-chemical and structure information. The objective of this research was to study the influence of laser fluence on the composition of the CP-Ti grade 4. Additionally, it was pretended to evaluate the surface modification of obtained layers. The electrochemical response of modified surface in Ringer’s physiological solutions at varying pH values was studied. Fretting test has been investigated in order to study the tribological behavior of the laser treated surface. Results showed that the laser treatments induce the insertion of light elements such as O2 and N2. Laser surface processing shifted the corrosion potential of CP-Ti grade 4 towards the noble side, as compared to the untreated one. After fretting tests, it was found that the steady friction coefficient was similar for all the layers, and quite lower than that measured for the untreated CP-Ti.

This work reports the development of a glassy carbon electrode (GCE), modified with an oxidized poly diphenylamine/multi-walled carbon nanotubes-β-cyclodextrin (OPDPA /MWCNT-β-CD) composite film, for ceftazidime determination. The OPDPA/MWCNT-β-CD film surface morphology was investigated using field emission scanning electron microscopy (FESEM) and cyclic voltammetry (CV). Ceftazidime was adsorbed onto the OPDPA/MWCNT-β-CD, at open circuit, for 240 seconds, and then oxidized in acidic media. The electrochemistry of ceftazidime oxidation was investigated using cyclic voltammetry and differential pulse voltammetry (DPV). Under optimum conditions, the peak current linearly increased with ceftazidime concentration, in the range of 5×10-8 M to 1×10-5 M. The obtained detection limit was 1.0×10-9 M. This sensor was employed for ceftazidime determination in the biological and pharmaceutical samples.

A comparative study of the corrosion behavior of pure magnesium and AZ91D anodes in reinforced cement concrete was undertaken in the present work. The steel reinforcements were electrochemically kept in contact with these anodes in a chloride atmosphere, and the half-cell potential drop was observed. Bare steel reinforcements were tied to the anodes and were also kept in a high chloride atmosphere to test the mechanical properties. The yield stress and ultimate tensile stress were found to decrease by approximately 50 MPa, while the reduction in percentage elongation was approximately 25% for reinforcements tied to AZ91D and pure Mg, at the end of 80 days, compared to the fresh steel reinforcement. The rate of corrosion of pure Mg was reportedly slightly higher compared to AZ91D, due to the presence of inter-metallics, as inferred through micro-graphs.

New corrosion inhibitors of benzimidazole derivatives, namely: 6-methoxy-2-(((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)sulfinyl)-1-vinyl-1H-benzo[d]imidazole (EMSB), 6-Methoxy-2-(((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)) sulfinyl)-1-(prop-2-yn-1-yl)-1H benzimidazole (MSVB) and 6-methoxy-2-(((4-methoxy-3,5-dimethylpyridin-2-yl)methyl)sulfinyl)-1-(phenacyl)-1-H benzimidazole (MSBP), have been synthesized and their inhibiting action on the corrosion of carbon steel in acidic bath (1 M HCl) has been investigated by various corrosion monitoring techniques, such as weight loss measurement, potentiodynamic polarization, adsorption, electrochemical impedance spectroscopy (EIS) and basic computational calculations. The results of the investigation show that the inhibition efficiency of all the three inhibitors increases with increase in concentration of inhibitors and decreases with increase in temperature. The inhibitors, MSBP, MSVP, and EMSB show corrosion inhibition efficiency of 98, 97 and 93% respectively, at 10-3 M and 303 K. EIS measurements showed an increase of the transfer resistance with the inhibitors concentration. Polarization studies showed that the studied inhibitors are mixed type in nature and the adsorption of benzimidazole is described by the Langmuir isotherm. In addition, density functional theory (DFT) calculations and molecular dynamics simulations (MDS) were undertaken to describe the electronic and adsorption properties of the synthesized inhibitors constituents, including the synergistic/dispersive interactive effects of the multiple adsorptions of the various active constituents in the inhibitor film on the iron surface. Also DFT and Molecular dynamic (MD) simulations were employed to correlate the experimental findings.

The electrochemical behaviour of nicotine extracted from commercial cigarette tobacco were studied in a blood media, at a glassy carbon electrode (GCE), using cyclic voltammetry technique. The nicotine compound oxidized the blood component in neutral media, at pH 7.4. The response was evaluated with respect to different pH values, scan rates, concentrations and temperatures. From the voltammogram of nicotine in a blood medium, it was found that the oxidation current peak of nicotine was +999 mV in acidic and alkaline media, which enhanced about twice in an acidic medium and disappeared in an alkaline medium. In its turn, at highly acidic media, three reduction current peaks appeared in the nicotine voltammogram in blood media. The electrochemical behavior of nicotine was investigated using cyclic voltammetry technique; the method was successfully applied for the determination of the nicotine compound which had a reversible redox couple in a blood medium from the peak potential separation of 100 mV. Also, it was found that the average value of the diffusion coefficient at the cathodic electrode was 4.075x1011 cm-2 s-1, and 22.625x1011 cm-2 s-1 at the anodic electrode.

The present work highlights the results of the application of a green inhibitor for material conservation. The anticorrosive performance of the pectin bio-polymer was established for the corrosion control of mild steel in a 1 M phosphoric acid medium. Electrochemical measurements such as potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) studies were adopted for the corrosion inhibition studies. The studies were carried out by varying the concentrations of pectin in the temperature range from 303 K to 318 K. Conditions were optimized to get maximum inhibition efficiency. The surface morphology study was done by scanning electron microscope (SEM), and elemental mapping was done using energy dispersive X-ray (EDX) studies to confirm the adsorption and interaction of the inhibitor with the material. Studies showed an increase in the inhibition efficiency with an increase in the concentration of pectin and also in the temperature. Maximum inhibition efficiency of 70% was achieved by the addition of 800 ppm of inhibitor. Pectin acted as a mixed type inhibitor by bringing down both cathodic and anodic reactions. Kinetic and thermodynamic parameters revealed chemical adsorption of pectin onto the mild steel surface. A suitable mechanism was proposed for the adsorption of pectin which was reaffirmed by the surface morphology studies. Pectin emerged as a potential eco-friendly green inhibitor for the corrosion control of mild steel, with economic benefits.

An irreversible electrode reaction influenced by the reversible potential dependent inhibition is theoretically analysed. The consequence of reactivation of the electrode surface is the continuation of electro-oxidation and the appearance of the second anodic peak in cyclic voltammetry. An indicator of the change of the electrode kinetics caused by the inhibitor is proposed.

In the present paper, the methanol extract from the leaves of Pistacia terebinthus L. (PT) was characterized by GC/MS analysis. It was tested as a corrosion inhibitor for iron in a 3% NaCl solution, using gravimetric measurements and electrochemical methods (potentiodynamic polarizations and electrochemical impedance spectroscopy). Fourteen compounds were identified; the major compounds are palmitic acid (31.5%), stearic acid (25.7%) and oleic acid (11.3%). The data showed that the tested extract offers good corrosion resistance. The constituents of the PT extract affected polarization resistance (Rp) and corrosion current density (icorr), demonstrating that the proposed inhibitor hinders corrosion reactions. The results obtained at 200 ppm are very interesting, and reach maximum values of 96.96%, 89% and 64.82%, respectively, which were confirmed by scanning electron microscopy (SEM), coupled with energy scattering of X-ray spectroscopy (EDX).

Electrochemical methods for the recycling of tungsten carbide (WC-10Co) resources suffer from passivation in the acidic medium caused by WO3 and also in NaOH electrolytes, due to hydroxide formation. We found that an ammoniacal solution is a promising electrolyte for sustainable electrochemical dissolution of both tungsten (W) and cobalt (Co). The ammoniacal medium performs greatly when supported with Cl-, SO42- and CO32- ions. Poor dissolution/corrosion tendency of WC-10Co in a diluted NH4OH solution enhanced many folds in the presence of Cl-, SO42- and CO32- ions. Among these supporting ions, Cl- emerged as the most suitable for the electrochemical leaching of W and Co from the WC-10Co, accompanying the least noble behavior of WC-10Co. An electrolyte composed of 150 g/L of ammonia and 5% (w/v) of NH4Cl yielded the maximum anodic current density. Microscopic examination of the electrochemically treated samples shows scattered active sites responsible for the oxidative dissolution of WC-10Co. The usefulness of W and Co dissolution in ammonia-additive salt followed the order NH4OH-NH4Cl>NH4OH-(NH4)2SO4>NH4OH-(NH4)2CO3.

Carbonaceous materials are used to generate composites for numerous purposes, due to their extraordinary properties. In this context, we have carried out a study on the modified properties, viz. thermal stability and specific capacitance of the composites fabricated by the introduction of a carbonaceous material (graphite and graphene oxide) into the Polyvinyl Butyral matrix. Since it has excellent adhesibility and dielectric permittivity, and it can be employed as an electrode in sensors, polyvinyl butyral is used in the current investigation, along with carbonaceous materials, for electrochemical and bandgap properties (HOMO-LUMO) studies. Spectroscopic FT-IR, XRD and SEM analyses remark the comprehensive entanglement of the two components. Various fabricated composites show an increased thermal stability, with a percentage of carbonaceous filler, as suggested by TGA. Cyclic voltammetry studies reveal that PVB acts as an excellent binder, and as a good matrix for the charge movement through it, because it has a good level of dielectric permittivity, thus enabling fabricated materials to be developed as good candidates for supercapacitive batteries

The electrochemical degradability of Al-20% Mg and hypereutectic Al-22% Si industrial alloys was evaluated in an aggressive acidic environment, namely 1 M H2SO4, using potentiodynamic polarization, linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS) techniques. The microstructure and constituting phases of the surface alloys were characterized by X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM), coupled with Energy Dispersive X-ray Spectroscopy (EDX). It was found that the two alloys’ corrosion behavior mainly depends on their crystalline phases. The presence of the active intermetallic β- Al3Mg2 phase in the Al alloy with high Mg content induced a preferential Mg dissolution, which caused a severe intergranular attack on this alloy by the corrosive solution. Meanwhile, the Al alloy containing high Si content, which presented the eutectic Al-Si phase, showed a uniform and weaker dissolution. It was also observed that a rise in temperature reduced the corrosion performance of the two studied alloys, as these corroded faster than pure aluminum.

Use of Amaranthus extract, as mild steel corrosion inhibitor, in a pickling paste with H2SO4, has been investigated. The electrochemical experiments were conducted to bring forth results regarding various parameters, viz., corrosion current, anodic polarization and cathodic polarization. The corrosion current gradually decreased with time, for both uninhibited and inhibited systems. Polarization curves values indicate that Amaranthus extract adsorption modified anodic dissolution mechanism, as well as cathodic hydrogen evolution. From the results, it is clear that both cathodic and anodic reactions were inhibited, and that inhibition increased as the inhibitor concentration increased in acidic media, but the cathode was more polarized. This result indicated that Amaranthus extract can be classified as a cathodic inhibitor, in a 4 N H2SO4 solution. Surface analysis via scanning electron microscope (SEM) showed a significant improvement on the mild steel plate surface morphology, in the presence of optimum inhibitor concentrations. Thus, by conducting these experiments, our aim is to use inhibited pickling acid in the paste form, so that it can be conveniently applied on large structures, as well as on small tools, to be pickled/cleaned. As a contribution to the current interest on environmentally friendly green corrosion inhibitors, the present study investigates the inhibiting effect of Amaranthus extract, a green inhibitor which is commonly known as Pigweed.