Portugaliae
Electrochimica Acta

Experimental electrochemical methods, combined with Monte Carlo simulations, have been employed to investigate the possibility of using 1-decyl-2-(decylthio)-1H-benzimidazole (T2) as corrosion inhibitor for mild steel in a 1 M HCl medium. This inhibitor was found to be of the mixed type. The results derived from EIS indicate that the charge transfer resistance has increased with the increase in the inhibitor concentration. The inhibitory mechanism was explored by the potential of zero charge (Epzc) measurement at the solution/metal interface. The inhibitor adsorption has followed Langmuir adsorption isotherm. Surface morphology results showed the compound adsorbed film on a mild steel surface. The molecule interactions with the mild steel surface were simulated based on Monte Carlo simulation approach using Fe(111) crystal surface as a representative metallic surface.

An expired drug with non-toxic characteristics has been evaluated as a corrosion inhibitor for mild steel alloy. The corrosion inhibition efficiency of the expired ethambutol drug in a 0.5 M HCl solution has been studied using weight loss, electrochemical impedance spectroscopy (EIS), electrochemical polarization, scanning electron microscopy (SEM) and molecular dynamics (MD) techniques. The results showed that the drug provides appreciable inhibition efficiency, more than 95% at the higher concentration, i.e., 1000 ppm. The Tafel polarization plots have shown that the expired drug acted as a mixed type inhibitor. Langmuir adsorption isotherm, along with physiochemical mode of interaction, has proved that the corrosion inhibition process accords with the isotherm. The outcomes obtained from all the experimental techniques and theoretically obtained information are in good correlation. MD simulations reveal that the studied compound adsorbs onto the surface of mild steel in the planar orientation.

Essential oil of Juniperus phoenicea (Cupressaceae) is extracted from the natural plant collected in Morocco. Extracted by distillation, its inhibiting action on the corrosion of mild steel in 1 M acidic media has been investigated by weight loss and various electrochemical techniques. Obtained results reveal that this naturally occurring substance is a very good inhibitor. The inhibition efficiency was found to increase with the oil content, attaining 83% at 1500 ppm. The oil of Juniperus phoenicea acts as a mixed-type inhibitor. The adsorption isotherm and the thermodynamic data of adsorption and activation are herein determined and discussed.

The purpose of our work is to improve the corrosion and mechanical shocks resistance of aluminium in the batteries, we have chosen tin as an element of addition by combining it with the aluminum and forming an Al-Sn alloy. By means of potentiodynamic polarization, electrochemical impedance spectroscopy, hardness evolution and optical microscopy, we have been able to study the effect of the tin addition on the corrosion of aluminum in NaCl as well as on its hardness and crystalline structure. We have also studied the influence of the electrolyte’s concentration in the battery (NaCl) and of temperature on the corrosion resistance of aluminum. The results obtained showed that the addition of tin have reduced significantly the corrosion rate of aluminum and increase its hardness. This means that the lifetime and the performance of the battery will be increased as well.

The objective of our work is to study, develop, characterize and apply a new epoxy macromolecular matrix in coatings, and their optimization for the conservation of marine heritage. Epoxy resins are technologically and nano-technologically compatible thermosetting macromolecule matrices that are easy to implement, according to their structures, viscosimetric and rheological properties, for the protection of the heritage possibly subject to atmospheric corrosion. In this sense, we have tested the new macromolecular binder, hexaglycidyl ethylene of methylene dianiline (HGEMDA), crosslinked and formulated for studying the behavior of steel coatings in a marine environment. In order to evaluate HGEMDA coating performance, we have studied its adsorption behavior onto the surface of corroded steel, and explained the interactions between the coating macromolecule and the steel surface. The coating effect on E24 steel was studied by quantum chemical calculations. The adsorption of HGEMDA onto the surface of E24 steel has been well described by the Quantitative Structure of Relation Property model (QSPR). The stationary and transient electrochemical studies are very interesting, since the prediction of the coating behavior was performed by the semi-empirical PM6, DFT methods and the method of three Becke compounds of parameter (UB3LYP), based on 6-311 G. All our calculations were performed using Gaussian software (03).

A new industrial electrodeposition of copper in an acidic medium using an environmental cinnamon extract has been developed. The obtained coatings were adherent and uniform, and their deposition rate has reached 23 µm/h. In addition, their quality has been improved by cinnamon extract addition. Cyclic voltammetry and electrochemical impedance spectroscopy have showed that the electrodeposition mechanism depends on the electrolyte constituents and the additive presence. The SEM observation indicated that the coatings morphology has been improved by cinnamon extract addition.

In order to evaluate the influence of aluminum on the corrosion resistance of lead anodes in 4 M H2SO4, as well as on the microcrystalline morphology of lead, different electrochemical and metallurgical studies were made such as potentiodynamic polarization, electrochemical impedance spectroscopy, hardness evolution, X-ray fluorescence spectroscopy and optical microscopy. The obtained results have shown that the addition of aluminum up to 1.5% in weight leads to a significant decrease of the corrosion and passivation rates (Icorr and Ipass) and it reduces the famous sulfation phenomena by facilitating the transformation of PbSO4 and PbO to PbO2. It also makes the micro-structure of Pb much stronger, which makes the Pb anodes more resistant to mechanical shocks within the battery. All of these improvements led to increase the lifetime of the conventional lead-acid battery up to 51.15%. Therefore, the new improved battery is more resistant, durable and more environment friendly.

Electrochemical aptasensor arrays have been recently used to detect several proteins reported as disease biomarkers, mainly due to their known advantages, that include high affinity, sensitivity, specificity and low costs, among others. This study describes the development of a label-free electrochemical multi-aptasensor array, for the simultaneous detection of human osteopontin (OPN), using two specific aptamers. To enable multiplexed protein assay, RNA and DNA aptamers were immobilized in the dual-screen-printed gold working electrodes via streptavidin-biotin interaction, and using the [Fe(CN)6]3−/4− as the redox probe for cyclic voltammetry measurements. The multi-aptasensor array herein developed exhibited a good response and selectivity to detect human OPN in the presence of other interfering proteins. Considering these preliminary results, the DNA/RNA dual aptasensor array could potentially be used as an analytical tool for the specific detection of human OPN, and for cancer diagnosis overall.

The corrosion behaviour of pure tin in an aqueous solution simultaneously containing Cl- and SO42- ions has been studied using electrochemical techniques, optical and scanning electron microscopy. Measurements were conducted under different chloride and sulphate ions concentrations. The potentiodynamic polarisation curves showed that the pitting potential, Epit, is independent from the variation of pH, temperature and chloride and sulphate concentration of the solution. In its turn, an increase of these parameters stimulates shifting of corrosion potential to more active values and leads to an increase of the corrosion and passive current densities. The electrochemical features were strongly supported by optical and scanning electron micrographs of the corroded surfaces of the pure tin samples after potentiodynamic polarisation experiments and immersion tests.

The inhibition of mild steel corrosion in a 1 M HCl solution by some natural free acids and antioxidants has been investigated by weight loss measurement, potentiodynamic polarization and DFT calculations. The experimental results have shown that these compounds exhibited a good corrosion inhibition. The inhibition efficiency increased with the inhibitor concentration. The adsorption of the inhibitor molecules onto the metal surface was found to respond to Langmuir adsorption isotherm for ascorbic, oleic and stearic acids, and to Temkin adsorption isotherm for palmitic acid. Tafel plot analysis revealed that these compounds acted as mixed type inhibitors, with more polarized cathodic than anodic curves. Regarding quantum chemical calculations, parameters such as energies of highest occupied molecular orbital and lowest unoccupied molecular orbital, energy gap, dipole moment, electronegativity, global hardness, softness, global electrophilicity, fraction of transferred electrons, ∆E Back-donation, Fukui and local softness indices have been performed on the tested inhibitors to investigate their structural and electronic properties, in order to provide an adsorption mechanism, and reveal the reactivity and selectivity of the molecules’ centers. The experimental results were in good agreement with theoretical results. The results for the natural acids were used to predict the linoleic acid inhibition efficiency.

The corrosion inhibition of carbon steel in a 1.0 M HCl solution, using 4-amino-2-(4 chlorophenyl)-8-(2,3-dimethoxyphenyl)-6-oxo-2,6-dihydropyrimido[2,1b][1,3]thiazine-3,7-dicarbonitrile (ACMPT) was investigated by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and quantum chemical calculations. Polarization curves indicate that the studied compound was acting as a mixed inhibitor with predominant cathodic effectiveness. The inhibition efficiency decreased with an increased temperature, and the thermodynamic and activation parameters obtained from this study were discussed. The adsorption behavior of ACMT follows Langmuir’s isotherm. In addition, Density Function Theory (DFT) calculations were performed on the studied molecule. The theoretical parameters obtained from this method are in good agreement with the experimental results.

The objective of this work is to achieve an analytical predictive model to study the influence of surface topography on the corrosion resistance of UNS S31600 stainless steel, in a solution of sodium chloride NaCl, at 6% by weight as electrolyte, applying the finite element method. The surface topography was given by the average roughness variation of a UNS S31600 work piece in superfinish turning, of which correlation with the corrosion resistance was examined. The analytical results show that corrosion physico-chemical parameters, polarization resistance, corrosion rate, corrosion potential, and current density have a very remarkable correlation with the surface roughness obtained by the superfinish turning. This is due to a very significant affinity between the plastic deformation depth obtained by turning, and the pits development on the work piece surface. The whole work was completed by an empirical analysis, in order to validate the analytical results obtained in comparison with the experimental results.

Titanium dioxide electrodes were prepared in three stages: (i) electrodeposition of Pt layer on a Ti substrate that was (ii) covered by a TiO2 thin film deposited by DC Magnetron Sputtering technique, at constant pressure of 0.8 Pa and oxygen partial pressure of 0.08 Pa, and (iii) annealed at 400 ºC. The structural (XRD) characterization of the films was performed, showing a predominant anatase-TiO2 phase, where some peaks corresponding to the Ti/Pt substrate were also observed. The average crystallite size for the films was 44 nm, showing the nanocrystalline nature of these anatase-TiO2 films. The surface morphology of the films was studied by scanning electron microscopy and revealed agglomerates of nanosized grains or particulates, distributed over the substrate surface with a ‘blooming flower-like’ appearance. The nanosized grains result in an increase in active surface area and also promote the formation of porous TiO2 films. The performance of Ti/Pt/TiO2 as anode was evaluated in the electrodegradation of an azo dye, the acid orange 7 (AO7). Assays were run at 0.1, 0.25 and 1 mA cm-2, using AO7 concentration of 50 mg L-1, and after 12 h assays colour (484 nm) and chemical oxygen demand removals up to 97 and 70% were obtained, respectively. The energetic yield decreased with the increase in current density, which is typical from a process controlled by diffusion. The platinization of the substrate improves the adhesion of the TiO2 film, increasing its lifetime, and increases the conductivity of the films, decreasing the energetic costs of the process.

The corrosion inhibition of mild steel in a 1.0 M hydrochloric acid solution by 2-(4,5-diphenyl-4,5-dihydro-1h-imidazol-2-yl)-5-methoxyphenol (P1) has been studied in relation to the concentration of the inhibitor, as well as to the temperature, using chemical (weight loss) and electrochemical techniques. All the employed methods were in reasonable agreement. The protection efficiency increased with an increased inhibitor’s concentration. The obtained thermodynamic adsorption parameters (∆G*ads, ∆H*ads, ∆S*ads) indicated that this polymer retarded both cathodic and anodic processes through physical adsorption, and blocked the active corrosion sites. It was also found that this compound obeyed the Langmuir’s adsorption isotherm.

People are implanted with orthodontic wires made of different materials, to regulate their teeth. The various toothpastes that they use during the course of the treatment may have a corrosive effect on these materials. Hence, the main objective of this study was to evaluate the corrosion behaviour of an SS 316L alloy in artificial saliva in the presence of a sparkle fresh toothpaste. An electrochemical study has been used to investigate the corrosion behaviour of this alloy. Scanning electron microscopy (SEM) imaging gave the morphological data for the sample; however, by using X-ray spectroscopy in conjunction with SEM (EDAX), the elemental composition was determined. Further, the analysis of the protective film formed on the metal surface was done using UV-visible absorption and fluorescence spectra. The corrosion resistance of the SS 316L system in various solutions decreases in the following order: AS+ toothpaste> toothpaste>AS. For AS+ toothpaste system, LPR= 1813475 Ohm cm2; Icorr = 2.464 x10-8A/cm2; Rct =14961 Ohm cm2; Cdl= 3.4088 x10-10 F/cm2 and impedance = 4.397 log z/Ohm. The high corrosion resistance offered by the toothpaste is due to the formation of a protective film. It confirmed that the active principles of the toothpaste ingredients have co-ordinated with the SS 316L metal ions through their polar atoms to form a complex.

In this study, lignin, a polyhydroxy compound, was extracted from black liquor of pulp and paper industry, and characterized. In view of the potential of such polyhydroxy compounds to adsorb onto metal surfaces, the corrosion inhibition efficiency of lignin on the corrosion of mild steel by 0.5 M H2SO4 has been studied using weight loss method, electrochemical polarization and impedance methods. The morphological changes of the surface during corrosion, in the presence and absence of the inhibitor, were studied by scanning electron microscopy. Results of these studies show that lignin does inhibit the corrosion of mild steel by sulfuric acid, and that the inhibition efficiency increased with lignin’s concentration.

The incorporation of composite and eco-friendly particles or fluids to develop new engineering materials has recently changed the coating world. In this study, a Zn-TiO2-TiB2 ternary alloy was produced from a sulphate bath on a mild steel substrate. Solanum tuberosum (ST) was later introduced to the bath to evaluate the effect of the organic additive on the ternary alloy. The study was conducted under constant plating time and current density. The fabricated matrix was systematically investigated using scanning electron microscope (SEM) coupled with an energy dispersive spectrometer (EDS) for structural properties. The micro hardness and anti-corrosion properties of the deposits were studied using, respectively, a diamond base micro hardness tester and potentiodynamic polarization method. The anti-wear properties and thermal stability of the electrodeposited alloy were studied using a MTR-300 abrasive tester and an isothermal furnace at 250 ºC. From the observed result, the coatings presented good stability, especially for Zn-TiO2-TiB2-ST, as compared to the Zn-TiO2-TiB2 coating. The addition of ST improved the hardness properties of the matrix from 182.4 to197.2 HV, and the corrosion rate from 0.9805 to 0.7711 mm/yr. This work established that co-deposition of mild steel with TiO2/TiB2/ST is promising in anti-wear and corrosion resistance properties.

The ability of benzyl nicotinate (BN) to inhibit the corrosion process of cold rolled steel (CRS) in a 1 M HCl solution has been investigated by weight loss measurements, potentiodynamic polarization and electrochemical impedance spectroscopic methods. The potentiodynamic polarization study revealed that BN acts as a mixed type inhibitor. The effect of temperature range (303-333 K) on the corrosion of steel was studied at different concentrations of BN. The efficiency of this inhibitor increases with an increase in its concentration, and decreases with rise of temperature. Free energy values revealed that BN molecule undergoes comprehensive adsorption. The adsorptive behavior of BN on CRS obeys Langmuir adsorption. The thermodynamic and activation parameters calculation helped in getting insight into the inhibitor mechanism. The DFT (density functional theory) studies of BN molecule also supported our experimental findings.

In the present work, the electrochemical oxidation of acid orange 7 (AO7) on a glassy carbon (GC) electrode has been investigated by cyclic voltammetry in different solvents: aqueous solvent (H2O), dimethyl sulfoxide (DMSO) and acetone (ACE), using sulfuric acid as a supporting electrolyte. The analysis of AO7 oxidation voltammograms in different solvents showed that the more donor numbers, the easier it becomes the oxidation of AO7. The experimental parameters show that the oxidation peak current of AO7 was linearly proportional to its concentration in a range from 0.04 mM to 0.2 mM. The limit of detection was estimated by gradually decreasing the concentration levels of AO7, and was found to be 6.6 µM.

The corrosion inhibition of aluminum by the extract of Trigonellafoenum-graecum L was studied in a hydrochloric acid 1 M solution using electrochemical polarization measurements and electrochemical impedance spectroscopy (EIS). Three organic solvents, pentane, dichloromethane (DCM) and ethanol, of different polarities, were tested. An inhibition efficiency of 86.6 %, 84.41 %, and 75.77 % was obtained by the addition of 1400 ppm of the extract using three solvents: DCM, ethanol and pentane, respectively. The potentiodynamic curves show that the decrease of aluminum corrosion in the presence of the fenugreek extract in a HCl 1 M solution mainly acts by a mixed process with an anodic tendency for both extracts with ethanol and with pentane; on the other hand, the extract with DCM showed a cathodic tendency. The temperature effect on the corrosion of aluminum indicates that the inhibition efficiency of the natural substance decreases with an increase in temperature. The inhibition efficiency values obtained from the polarization curves are in good agreement with those of EIS.