Portugaliae
Electrochimica Acta

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.

The need to improve the structural properties of materials in petrochemical industry, due to recurring failure, has motivated this study. The effect of deposition potential on structural integrity, surface topography and micromechanical progression of Zn based induced aluminium and TiO2 alloy coating series on mild steel was studied. The wear stability and microhardness behaviour of the developed composite coating was examined via, respectively, sliding reciprocating rig and dura scan diamond based microhardness tester. The structural reliability was inspected with scanning electron microscope equipped with EDS, and atomic force microscope. The results showed that the superb structural crystal resulted into a significant increase in the microhardness, and into a decrease in wear plastic deformation in a non-lubricated system. The precipitation of the deposits enforces stable crystal orientation and compact grains growth. The work has established that up to 13wt% TiO2 on zinc rich bath, a solid composite coating on mild steel, can be used to improve the service life of coating for stable structural properties.

The electrochemical behavior of pramipexole dihydrochloride was studied at carbon paste electrodes in 0.04 M Britton–Robinson buffer of pH 6.08, using cyclic and differential pulse voltammetric techniques. The oxidation of pramipexole dihydrochloride is an irreversible diffusion-controlled process. A differential pulse anodic voltammetric procedure has been developed for determination of the drug over the concentration range of 1.20 – 8.23 μg/mL, with detection and quantification limits of 0.21 and 0.68 μg/mL, respectively. The proposed method was successfully applied for the determination of the drug in its commercial tablets.

This work ultimately pays careful consideration to a method that respects the environment, and that can be developed across the accumulation of research to reduce the corrosion of metals in sea water. Extracts of Ziziphus lotus (wild jujube) were tested as a corrosion inhibitor of copper in sea water, using polarization methods and weight loss measurements. We also present by SEM the morphology of copper surface analyzed after immersion in inhibited and uninhibited electrolytes. The inhibition efficiency of Ziziphus lotus extracts was calculated and compared. We note good agreement between these methods. The obtained results revealed that the tested inhibitor significantly reduced the kinetics of the corrosion process of copper. Its efficiency increases with the concentration, and attained 93% at 5 g/L. The effect of temperature on the corrosion behavior of copper in natural sea water was also studied in the range of 293 K and 323 K, to determine thermodynamic data of activation.

Four different herbal compounds, Anise (Pimpinella Anisum), Caraway (CARUM Carvi), Cumin (Cuminum Cyminum) and Hibiscus (Hibiscus Sabdarriffa) have been tested as green corrosion inhibitors for copper exposed to 0.5 M NaCl. The corrosion inhibition has been studied using electrochemical noise analysis (EN) and electrochemical impedance spectroscopy (EIS). The comparative analysis of the results obtained showed that EN is an effective tool for screening of new corrosion inhibitors. Analysis of noise data demonstrated the need of removal of the trends in the potential and current fluctuations during the measurement periods. The results gathered showed very good inhibition efficiency. Generally, EN showed a good correlation with EIS in this study.

In the present work, the inhibitory properties and the adsorption mechanism of penicillin G for the corrosion of Fe-19Cr stainless steel in an HCl solution were investigated. Electrochemical methods, the open circuit potential (OCP) and the current potential curves (I-V) were used. The inhibition efficiency of the penicillin G was calculated and found to be up to 60% for hydrochloric acid. The adsorption of this inhibitor was described by Langmuir isotherm, and the negative values of Gibbs energy indicate the nature of interactions between the inhibitor molecules and the metal surface.