Portugaliae
Electrochimica Acta

The goal of our work is to develop, study, characterize and apply new epoxy macromolecular matrices in the coating process, and to optimize them in the conservation of marine heritage. Epoxy resins are technologically and nano-technologically compatible thermosetting macromolecule matrices, which are easy to use, thanks to their structures and viscosimetric and rheological properties, able to protect the heritage subject to atmospheric corrosion. In this paper, we tested the synthesized, crosslinked and formulated novel macromolecular nanoglycidyl trihydrazine 4,4,4-tripropoxy ethylene tribisphenol A (NGTHTPETBA), used as an anti-corrosive coating for E24 steel in 3.5% NaCl. In order to evaluate the inhibiting performance of the NGTHTPTBAE coating for E24 steel corrosion, and to examine its coating behavior, we applied the different E1(NGTHTPETBA/MDA) and E2(NGTHTPETBA/MDA/PN) formulations. The stationary and transient electrochemical studies are very revealing.

Benzyl dimethyl dodecyl ammonium chloride-zinc ion system, as quaternary ammonium salt (QA-Zn+2), was investigated as corrosion inhibitor for carbon steel in a 2.0 M sodium chloride solution, by different techniques such as weight loss, open circuit potential, potentiodynamic polarization and electrochemical impedance spectroscopic techniques. The inhibition efficiency of the used system (QA-Zn+2) increases with increasing mixed inhibitor concentrations and with rising temperatures. A synergistic effect exists between QA and Zn+2. Potentiodynamic polarization curves indicate that the used system mainly acts as an anodic mixed inhibitor. The polarization resistance values were (Rp) increased, and the interface capacitance (Cdl) was decreased in the mixed inhibitor system (QA- Zn+2) presence, more than in the case of individual inhibitors. The corrosion inhibition is due to the adsorption of (QA-Zn+2) onto the metal surface, and the formation of a barrier film that separates the metal from the corrosive medium. The maximum inhibition efficiency of 98% was obtained at 200 QA and 50 ppm Zn+2 of the mixed inhibitor system, due to a synergistic effect.

The inhibitive action of Piper guineense (uziza leaf) extract on the corrosion of mild steel in a 2 M H2SO4 medium has been studied using weight loss method. The collected leaf samples were rigorously grounded and squeezed, with the resultant gel extract used for the weight loss determination at 1.0%, 2.0%, 3.0%, 4.0% and 5.0% v/v concentrations, respectively. Therefore, rectangular mild steel coupons in a 2 M H2SO4 solution were also employed to determine the amount of weight loss in the absence and presence of Piper guineense extract at temperatures of 303 K, 313 K and 323 K. The results show that mild steel corrosion inhibition increases with increasing concentrations of Piper guineense extract, showing greater efficiency at higher temperatures of 313 K and 323 K. Moreover, Piper guineense extract can effectively perform as a green and non-toxic inhibitor for mild steel corrosion in acidic environments.

Concrete is one of the most commonly used construction materials, but there is a need to develop a new and sustainable technology to make it more affordable. With the advancement in technology, concrete is no longer seen as a composite of three elements (binder, aggregate, and water). The distinctive workability properties of SCC make it unique in the concrete industry. This review has assessed the materials, strength and rheological properties of agricultural waste, industrial waste and mineral additives in SCC production. The effect of the utilization of these additives and replacements on structural, mechanical and rheological properties of SCC has been studied. This review has revealed that the use of both industrial and agricultural waste enhances the strength properties of SCC. Additionally, the use of agricultural waste improves the rheological properties of fresh concrete. The utilization of expansive materials should be discouraged in SCC production. This review has revealed that SCC developments ensure a good balance between deformability and stability. It is therefore recommended that SCC is utilized in pavement construction, particularly when high axle load is expected.

In this study, Fenton, photo-Fenton, electro-Fenton, anodic oxidation and heterogeneous photocatalysis advanced oxidation processes (AOPs) have been applied to degrade reactive yellow 17 (RY17) dye in an aqueous solution. Comparison of these techniques for oxidation efficiency was undertaken. The results showed better performance with the use of a heterogeneous photocatalysis process. Degradation efficiency was observed in the order: heterogeneous photocatalysis > photo-Fenton = electro-Fenton > anodic oxidation > Fenton. Even though complete RY17 dye degradation has been observed with heterogeneous photocatalysis, photo-Fenton and electro-Fenton processes, the heterogeneous photocatalysis process has showed complete RY17 dye removal within 30 min, whereas in the case of photo-Fenton and electro-Fenton processes, no RY17 was detected after 60 min. Fenton and anodic oxidation processes have required more time for complete RY17 degradation. The RY17 degradation kinetics was studied and compared in all processes. The results showed higher rate constant values for heterogeneous photocatalysis (kapp = 0.2 min−1), photo-Fenton (kapp = 0.126 min−1) and electro-Fenton (kapp = 0.122 min−1) processes.

The chemical composition of Jatropha curcas seeds oil was determined using chromatography gas (GC/MS) analysis after the esterification of fatty acids to methyl ester (FAME). The obtained results show that the average yield of Jatropha curcas seeds oil reached a maximum value of 50%. The seeds oil fatty acids carbon chain was composed of palmitic, oleic and linoleic acids. The percentage of unsaturated fatty acids reached a value of 77%.The new developed formulation containing Jatropha curcas seeds oil (labeled as JAC) was tested as a friendly iron corrosion inhibitor in an acidic medium by potentiodynamic polarization and Electrochemical Impedance Spectroscopy (EIS) techniques. The surface analysis was performed using Scanning Electron Microscopy (SEM). The electrochemical measurements show that the JAC formulation is a mixed type inhibitor. The obtained inhibition efficiency results increase with higher inhibitor concentrations, to attain a maximum value of 97% at 250 ppm. Furthermore, the protective effect is reinforced by increasing the immersion time and the rotation speed of the working electrode.

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.