Portugaliae
Electrochimica Acta

The corrosion inhibition effect of ethanol extract of Acacia nilotica leaves (ANLE) on mild steel in 0.1 M H2SO4, containing 0.1-0.5 g/L, has been studied using weight loss, Potentiodynamic Polarization (PDP), Fourier Transforms Infra-Red (FTIR) spectroscopy, UV-visible spectroscopy, High-Performance Liquid Chromatography (HPLC) and Scanning Electron Microscopy (SEM) methods. The results from weight loss and PDP show that the inhibition efficiency depends on the concentration of the plant extract, as well as on the time of exposure of the mild steel samples in H2SO4 solutions. The optimum inhibition efficiencies of the extract obtained from weight loss and potentiodynamic measurements were found to be 87.57% and 61.85%, respectively. Thermodynamic parameters, such as Ea, ΔH, ΔG and ΔS, were evaluated at 0.5 g/L, and the results were found to be -78.54 kJ/mol, 74.66 kJ/mol., -17.92 kJ/mol and -90.59 kJ/mol, respectively. From the calculated values of activation energy and free energy of adsorption, and from the trend in the variation of inhibition efficiency with temperature, the inhibitor mechanism of adsorption was found to be physical adsorption, exothermic, spontaneous, being best described by Langmuir adsorption model, because the regression coefficients (R2) values calculated from the plots were closest to unity, confirming a highest degree of linearity. Mild steel surface morphology, in ANLE presence and absence, was studied using SEM. FTIR spectroscopy and UV-visible spectroscopy analyses were used to confirm the adsorption process onto the metal surface. Spectra analysis obtained from FTIR study indicated that ANLE was adsorbed onto the mild steel surface via C-O and N=O functional groups. HPLC was also used to find the main component responsible for inhibition, at 5.990 min, which was Catechin. The obtained results revealed that ANLE acts as a good inhibitor and could serve as an effective mild steel corrosion inhibitor in a 0.1 M H2SO4 solution.

This work is a contribution to the study about the inhibition of mild steel corrosion in a molar hydrochloric acid medium by some benzoxazol derivatives compounds. The study was carried out using gravimetric and electrochemical methods (stationary and transient). We have considered the influence of the inhibitor concentration, the temperature of the medium and the duration of the immersion of the metal sample in the aggressive medium. These studies are complemented with theoretical calculations aimed to correlate the results obtained from experimental measurements using the DFT method. The results obtained in this work through gravimetric and both transient and stationary electrochemical methods showed a satisfied coherence. Theoretical calculations also revealed a good correlation with the experimental results for our compounds.

The inhibition effect of Cefalexin on mild steel corrosion in sodium chloride has been examined with the use of electrochemical potentiodynamic polarization techniques, weight loss measurements and computational studies. Cefalexin showed good protection ability by adsorbing onto the mild steel surface. The mixed inhibition characteristics of Cefalexin were revealed by the potentiodynamic polarization results. The inhibitor efficiency was found to be above 65%, obeying the Langmuir and Freundlich isotherm law, with a correlation regression coefficient of R2= 0.9984 and R2= 0.9488, respectively, establishing the reliability on Cefalexin as an inhibitor.

This work consists in applying and studying the new pentafunctional phosphoric polymeric architecture – pentaglycidyl ether pentaphenoxy phosphorus (PGEPPP) – on the behavior of its coating, in a marine environment. First, we applied the new macromolecular pentafunctional epoxide (PGEPPP) binder, crosslinked by methylene dianiline and formulated by a natural phosphate, to E24 carbon steel, in the presence of two formulations, F1 (PGEPPP/MDA) and F2 (PGEPPP/MDA/PN). Then, we have studied the behavior of the anticorrosive coating on the metal substrate, in 3.5% NaCl. Indeed, the gravimetric, stationary and transient electrochemical studies of the composite (PGEPPP/MDA/PN) are very interesting and reach maximum values which are equal to 94%, 95% and 91%, respectively. We then proceeded to the prediction of the quantum parameters of the new pentafunctional phosphorus epoxy resin; these parameters were calculated according to the method of the Theory of Functional Density (DFT), at the level of 6-311 G (d,p) basis sets. Finally, the results obtained by the Monte Carlo simulation are in very good agreement with the data of the DFT theory and with the experimental data.

The inhibitive effect of different extracts of the Tribulus terrestris plant was estimated on the corrosion of mild steel in 1 M hydrochloric acid (HCl), using weight loss and Tafel polarization curves. The inhibition efficiency was increased with higher extracts concentrations. The effects of temperature on the corrosion behavior of mild steel in 1 M HCl, with the addition of extracts, were also studied. The inhibition efficiency obtained using tafel polarization curves and weight loss measurement gave similar results. Polarization curves showed that different extracts of the Tribulus terrestris plant behave as mixed type inhibitors in hydrochloric acid. The obtained results showed that the different extracts of the Tribulus terrestris plant act as an effective green inhibitor of mild steel corrosion in a hydrochloric acid solution. The corrosion inhibition of mild steel was confirmed by the scanning electron microscopy (SEM) study, which shows a good metal surface, without the presence of corrosion products.

The concentrations of lead and cadmium were determined in markets of hair dyes samples in Morocco. Sixteen synthetic and natural hair dyes were selected. The metals were analyzed after mineralization with nitric acid and hydrogen peroxide. The content was determined using differential pulse polarography and the analytical method was validated. The method was linear with a correlation coefficient value (r) that ranged from 0.992 to 0.999. The limit of detection (LOD) was 0.080 and 0.43 ppm for Pb and Cd, respectively. Finally, the concentrations of the two metals in the different hair dyes samples ranged from LOD to 3617.02 ppm for Pb and from LOD to 459.57 ppm for Cd. The majority of the concentrations were above acceptable levels for cosmetics. It has been demonstrated that heavy metals induce toxicity to human body even at a low level, hence the need to strengthen the control of cosmetic products by the competent authorities in Morocco.

A selective method is presented for the simultaneous determination of Pb and Zn in seawater samples, using Differential Pulse Adsorptive Cathodic Stripping Voltammetry (DPAdCSV). In preliminary studies, it has been proven that Pb and Zn react with calcon, giving rise to the formation of complexes which have adsorptive characteristics with a hanging mercury drop electrode (HMDE) and undergo reduction. The optimum parameters and conditions for determination are investigated. The optimal parameters for DPAdCSV of calcon were found to be 0.3 mol L-1 of acetate buffer, with pH 5, 0.02 mmol L-1 of calcon, adsorptive accumulation potential (Eads) of -0.1 V and adsorptive accumulation duration (tads) of 70 s. Ten replicates were performed, giving RSD values of 1.2% for Pb and 0.4% for Zn. Recovery values were in the range from 98% to 105% for both Pb and Zn. The calibration graphs were linear in the range from 5 to 210 ng mL-1 and 5 to 200 ng mL-1 for Pb and Zn, respectively. The limit of detection (LOD) was 0.01 ng mL-1 for Pb and 0.05 ng mL-1 for Zn. The interference of some common ions was studied and it was concluded that the method could be successfully used to determine the concentration of Pb and Zn in seawater samples.

Sodium dodecyl sulfate modified carbon paste electrode (SDSMCPE) was prepared as a sensor for Tartrazine (TR) detection, at 0.2 M PBS, with pH 6.5. TR Electrocatalytic activity was found to be significantly improved compared to those obtained using a conventional paste electrode. TR electrochemical oxidation was investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). SDSMCPE showed TR electrocatalytic oxidation in the linear range from 2×10-5 to 5×10-5 M and from 6×10-5 to 1.1×10-4 M, with the detection limit of 52×10-7 M. The proposed SDSMCPE-sensor exhibited enhanced electrochemical sensing, selectivity and stability for TRdetection. Finally, the use of a SDSMCPE-sensor was demonstrated for TRdetection in a lemon yellow powder sample.

Three different films modified with silver species were considered to enhance the corrosion resistance of AZ91D Mg alloy and to impart its surface with antibacterial activity. First, coatings were electrodeposited under potentiostatic conditions in electrolyte solutions containing Na2MoO4 and/or Ce(NO3)3 as main compounds, and H2O2, ascorbic acid or citric acid as additives. Incorporation of silver species was done by immersion of the samples in AgNO3 solutions. The obtained modified films were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The corrosion protection properties of the films were examined in a simulated physiological solution by open circuit measurements, linear polarization and electrochemical impedance spectroscopy (EIS). The antibacterial effect of the coatings was evaluated using Escherichia coli bacteria. Cerium and molybdenum-based coating modified with silver provides superior antibacterial and anticorrosive properties compared to the other films studied.

The present work is focused on the influence of the metal salts on the photocatalytic efficiency of TiO2 for the elimination of E 131 VF food colorant. Two series of TiO2 photocatalysts loaded with Fe(II) and Cu(II) were prepared by using the wet impregnation method. The samples were characterized by XRD, IR, Raman and scanning electron microscopy. The degradation of the food colorant was followed by the measurement of the absorbance. The kinetics of degradation fitted well to the zero pseudo order with Cu-TiO2, but it followed the 1st order with Fe-TiO2. In general, the photoactivity of TiO2 was reduced by the presence of the transition metal ions, even at low molar ratio %. The recalcination of the doped samples at higher temperatures reduced more the degradation activity. Several reasons were suggested to explain the dramatic decrease in the activity of the prepared samples.

Molecular modelling approach has been used for the prediction of anticorrosion properties of 1, 2, 4-triazole derivatives on steel in acidic medium by the quantum chemical calculation and molecular dynamics (MD) simulation methods. Quantum chemical parameters such as the highest occupied molecular orbital (E-HOMO), the energy of the lowest unoccupied molecular orbital (E-LUMO), energy band gap (ΔE), dipole moment, global electronic chemical potential (μ), chemical softness (σ), chemical hardness (η) and electrophilicity (𝜔) have been calculated and discussed. The reactive sites of the inhibitor molecules were found to be on the nitrogen-atom of the Triazolic ring and on the π-electron centers. Furthermore, molecular dynamics simulation was applied to search for the best inhibitor adsorption configuration over Fe (110) surface. The best adsorption energy was found to be -430.27 kcal/mol (inhibitor 3). The adsorptions occurred via chemisorption.

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.