Portugaliae
Electrochimica Acta

Atomic absorption spectroscopy (AAS) of samples taken from the organic phase of a water/1,2-dichloroethane (1,2-DCE) interfacial electrochemical cell, rendered non-polarizable by the tetraphenylarsonium common-ion, revealed significant transfer of heavy metal from the aqueous phase. Heavy metal concentration found within 1,2-DCE cannot be explained via ion pair formation between the metallic species and the common-ion, nor by ion pair formation between the metallic species and the hydrophobic anion of the organic phase. Results suggest that metal may have been anomalously transferred into 1,2-DCE within water-in-oil droplets formed by spontaneous emulsification of the interfacial region.

The presented work was pivoted on iron (II) determination in deep groundwater wells samples by using anodic stripping technique at an iodine-coated platinum electrode. The developed method was based on a preconcentration step for five min., followed by the potential scanning of an iodine-coated platinum electrode between the limit of hydrogen evolution (-0.25 V) and the beginning of iodine desorption from the electrode surface (+0.85 V). The anodic peak of the deposited iron to iron (II) oxidation was clearly centered at ca. 0.74 V. The anodic peak current showed an excellent linear response (R2 = 0.996), within an iron (II) concentration range from 1 to 100 ppm. The obtained limit of detection (LOD) was 0.26 ppm and the limit of quantification (LOQ) was 0.85 ppm. Within the iodine-coated platinum electrode potential window the possible interferences by several ions were evaluated. The developed method was examined by iron (II) concentration determination in deep groundwater wells. The statistical comparisons between the two methods showed the absence of any significant difference between the obtained Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES) values and our voltammetric method results, at P = 0.05.

Metallic materials remain an indispensable element in industries. The present study is aimed at the assessment of Parinari polyandra leaves inhibition properties on mild steel in a 1 M HCl solution. This was investigated using gravimetric and electrochemical methods. Physicochemical and spectroscopic analyses of the leaves extract were done using standard methods. A yield of 19.82% was obtained, while the leaves extract FTIR spectra showed bands of 3404 cm-1 and 2926 cm-1, which indicated the presence of a strong band of phenolic O-H and C-H stretch functional groups, respectively. A maximum corrosion inhibition efficiency of 97.22% was obtained. Langmuir adsorption isotherm fitted the inhibitor data well. From electrochemical methods, the corrosion rate value of 17.626 mmpy obtained for the uninhibited mild steel was higher than 0.02044 – 2.2267 mmpy range values recorded for the mild steel surface covered with P. polyandra leaves extract in an acidic medium. SEM images showed the leaves extract inhibition effect against mild steel corrosion in a 1 M HCl solution. Electrochemical analysis using the Tafel plot also showed the leaves extract corrosion inhibition capacity, suggesting a mixed type inhibitor. Thus, P. polyandra leaves extract might act as a green corrosion inhibitor for mild steel utilized in industrial applications.

The corrosion inhibition of newly synthesized Schiff base derivatives, namely (E)-3-(1-((2-aminophenyl)imino)ethyl)-4-hydroxy-6-methyl-2H-pyran-2-one (FMO), (E)-3-(1-((3-aminophenyl)imino)ethyl)-4-hydroxy-6-methyl-2H-pyran-2-one (FMM), and (E)-3-(1-((4-aminophenyl)imino)ethyl)-4-hydroxy-6-methyl-2H-pyran-2-one (FMP) was investigated for mild steel, in a 1.0 M HCl medium, using weight loss, electrochemical impedance spectroscopy, potentiodynamic polarization and theoretical calculations. FMO, FMM and FMP inhibition effectiveness increased with higher inhibitors concentrations, and decreased with a rise in temperature. Polarization studies showed that FMO, FMM and FMP were of mixed type nature. The results obtained from AC-impedance technique were analyzed to model the corrosion inhibition process through a suitable equivalent circuit model, where a constant phase element (CPE) has been used. FMO, FMM and FMP were found to obey Langmuir adsorption isotherm and Kinetic-Thermodynamic Model of El-Awady. Quantum chemical calculations were used to provide molecular based explanations for FMO, FMM and FMP inhibitive effects. Monte Carlo simulation studies and experimental results were in good agreement

The electrochemical corrosion behaviour of pipeline steel in a sulphuric acid environment, in the absence and presence of commercial Rutin (CR), was studied using electrochemical techniques. The polarization and impedance curves showed an excellent corrosion inhibition characteristic of Rutin, which was more cathodically controlled. Temperature increase slightly improved CR corrosion inhibition capacity. CR was able to increase the charge transfer resistance up to four days, and showed a smoother corrosion surface morphology in the study environment. Analysis of the corrosion surface film showed that Rutin was chemically adsorbed onto the pipeline steel surface.

Kinetics regularities of hydrogen evolution reaction (HER) on Armco iron and copper anodic ionization, covered with a hydrocarbon film based on I-20A oil with a fixed amount of gun grease of the highest quality (GGHQ), were studied at room temperature. The measurements were carried out in aqueous and methanol solutions with the electrolyte composition of x M HCl + (1 - x) M LiCl and 0.1 М HCl + х М LiCl + (3.9 - х) М LiClO4. The Tafel slope coefficients values, and the orders of reactions, with respect to hydrogen ions (Fe, Cu) and chloride-ions (Cu) were estimated. The effect of oxyethylated amines (OEA), introduced into the solution or hydrocarbon surface coating, on the kinetics of electrode processes, for iron and copper, has been studied. It is shown that HER mechanism on Armco iron and copper anodic ionization does not change in the presence of a hydrocarbon coating on the metal surface. Large OEA molecules freely penetrate from the solution through the hydrocarbon coating to the metal surface, changing partial electrode reactions kinetics. The results are interpreted taking into account the hydrocarbon films surface porous structure.

A new inhibitor Schiff base ether ligand, L1, di[(4-phenylamino)2,4-dihydroxy salicylaldehyde], was synthesized and characterized using mass spectra, elemental analysis, IR spectra, UV-Vis spectra, 1H NMR spectroscopy and thermal analysis. Electrochemical properties were investigated using cyclic Voltammetry (CV). The corrosion inhibition effect of the new prepared Schiff base was examined on mild steel (X48) in a 1 M HCl solution, by using gravimetric and electrochemical measurements. The potentiodynamic polarization results showed that the investigated Schiff base acted as a mixed kind inhibitor (cathodic/anodic), with some cathodic predominance. The adsorption procedure on X48 surface obeyed Langmuir isotherm. The associated adsorption activation factors and thermodynamic parameters were evaluated and interpreted. The inhibitor layer formed on the metal surface was characterized by AFM and SEM. The solid-state molecular geometry has been studied with the theoretical data obtained by density functional theory (DFT). Furthermore, the interaction between the inhibitor and Fe (1 1 0) surface was achieved by molecular dynamics simulations.

Two carbon paste electrodes for oxymetazoline hydrochloride were constructed based on ion pair complexes of this drug, with sodium tetraphenylborate (NaTPB) or ammonium reineckate, using dibutyl phthalate and dioctyl phthalate as solvent mediators, respectively. The developed electrodes displayed a fast, stable response over the concentration range from 3.98x10-5 to 1x10-2 M oxymetazoline hydrochloride, with a near-nernstian slope of 59.0, 58.2 mV of concentration decade-1 and a limit of detection (LOD) of 3.31x10-5 and 3.72x10-5 M, in the oxymetazoline-tetraphenylborate and oxymetazoline-reineckate cases, respectively. The developed electrodes have been successfully applied for oxymetazoline hydrochloride determination in the Afrin nasal drop pharmaceutical formulation.

Low-carbon steel electrodes were buried in sterilized and bacterial media. The potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) were sequentially carried out on buried electrodes. The corrosion potential, on the steel electrode buried in a sterilized medium (without sulphate reducing bacteria), was found to be more negative than that of the electrode buried in the sulphate reducing bacteria (SRB) medium. Cathodic and anodic curves electrodes buried in a SRB medium showed the highest current density. Clearly, three phases were observed during the SRB growth within an incubated medium. EIS measurements showed that the effects of biofilms on steel electrodes varied with time. From the bacterial medium, EIS results showed an optimum cathodic protection (CP) potential of -1450 mV Cu/CuSO4. Surface morphologies of electrodes buried in bacterial media revealed dimples on the entire electrode surface, when the slow strain rate tensile test (SSRT) was carried out in air, while quasi-cleavage was discovered on the steel electrode, when the applied CP potential was -950 mV Cu/CuSO4. At -1450 mV Cu/CuSO4, corrosion products were seen all over the electrodes, and a complete cleavage occurred on them at -1890 mV Cu/CuSO4.

The use of plant extracts as corrosion inhibitors has been increasing greatly in recent studies. The inhibitive effect of sumac, Rhus Coriaria (RC), a Lebanese plant, and Quercetin, one of its chemical constituents, on mild steel corrosion, in 0.5 M HCl and 0.5 M H2SO4 solutions, was studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, atomic force spectroscopy (AFM) and Fourier infrared spectroscopy (FTIR) techniques. Potentiodynamic polarization curves indicated that both RC and its chemical constituent, Quercetin, behave as a mixed type inhibitor in both acidic media. The dissolution process of RC and Quercetin occured under activation control, as showed by EIS measurements, and the corrosion inhibition is the result of the inhibitor adsorption onto the metal surface. Inhibition by RC extract was found to be greater in 0.5 M HCl than in 0.5 M H2SO4 solutions; RC extract also proved to be a better inhibitor than its chemical constituent, Quercetin, in both acids. Thermodynamic parameters indicate that the inhibition process on the steel surface was due to spontaneous physical adsorption of RC and Quercetin onto it. The adsorption model was found to obey thermodynamic-kinetic model and Flory-Huggins model. Surface analysis by AFM spectroscopy investigated the formation of the adsorbed protective film onto the mild steel surface.

In order to evaluate the influence of magnesium on the corrosion resistance of lead anodes in H2SO4 4 M, as well as on the microcrystalline morphology of lead, different electrochemical and metallurgical studies were made, such potentiodynamique polarization, electrochemical impedance spectroscopy, microhardness evolution, X-ray fluorescence spectroscopy and optical microscopy. The obtained results have shown that the addition of magnesium up to 1.5% in weight leads to a significant decrease in the corrosion current density (Icorr) and therefore, it increases the corrosion inhibition efficiency to 83% 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. We have also studied the effect of temperature on the corrosion of the new casting alloys. We found that an increase in temperature led to a decrease in its effect on the corrosion of alloys, compared with that of pure lead. Therefore, the new improved battery is more resistant, durable and more environment friendly.

In the present work, a simple and low-cost protocol for determination of gliclazide using modified screen-printed electrodes (SPE) was reported. The immobilization of magnetic core-shell manganese ferrite nanoparticles (MCSNP) onto SPE provides a unique opportunity for charge transfer process. Consequently, the electroanalytical sensing of gliclazide was explored at the modified SPE surface. The response of the modified electrode was linear, in the concentration range from 0.5 to 300.0 μM, and a detection limit of 100 nM was obtained. The proposed method was successfully employed for gliclazide determination in pharmaceutical and human urine samples. The method showed tremendous reproducibility and intra- and inter-day stability, and has proved to be highly reliable for gliclazide analysis in clinical samples.

Recently, there were reported investigations in the field of corrosion prevention, about finding effective environment-friendly alternative inhibitors, to replace toxic and harmful compounds. In the present review, the corrosion inhibition of some materials in various corrosive media, using imidazole derivatives, is summarized. Several organic compounds reported by many researchers are herein presented. This review considers previous studies conducted on various inhibitors, and provides an overview of some experimental techniques performed in order to investigate their corrosion properties.

In this paper, the performance of a composite particle for the deposition of ZnO/Cr2O3 on a zinc electrolyte was examined. Its susceptibility to corrosion in 3.5% NaCl, using linear polarization, was investigated. The developed crystal was characterized by using scanning electron microscope (SEM) equipped with an energy dispersive spectrometer (EDS). The strengthening properties of the coated samples, i.e. the mechanical response, were studied using a high sensitive diamond microhardness indenter and a MTR-300 rigid wear tester. From the results, the effect of the composite coatings interestingly influenced the performance regarding microhardness, durability, corrosion mitigation and wear damage. In general, the micro-hardness value for the Zn-ZnO material was 125.0 HVN, while it was 130.5 HVN for Zn-8ZnO-16Cr2O3 composite coating. For Zn-8ZnO-20Cr2O3, a better hardness performance was noted with 138.0 HVN. From the wear study, Zn-8ZnO shows 0.018 g/min dissociation against the counter body with the best wear performance obtained at 0.005 g/min. The corrosion properties of the developed composite coating also tend towards a more positive region, with a corrosion rate of 0.850 mm/yr. This shows that the role of composite particulates maximally contributes to improve the strengthening characteristics of the developed coating.

The adsorption capacity of activated carbon and activated carbon with amide group towards Ni(II), Zn(II) and Co(II) from aqueous solutions was studied in varying treatment conditions such as contact time, weight of sorbent, pH and initial concentration of treated metal ions. The adsorption capacity was investigated by batch experiments. The results showed that the removal percentages were enhanced by increasing the weight of the added sorbent, contact time, pH of the solution and the initial concentration of treated metal ions. The optimum order of increasing removal percentages of metal ions by using activated carbon (AC) prepared from sawdust of beech wood at pH=5, with an initial concentration of metal ions of 100 mg/L, and after two hours of shaking, was: Zn(II)

This study reports the evaluation of the anticorrosive performance of polymer epoxy resin, namely, Diglycidyl ether 4, 4’-dihydroxydiphenylsulfone (DGEDDS) and its polymer composite reinforced with Titanium Dioxide (TiO2), for carbon steel (CS) corrosion, in 3% wt. NaCl, using experimental analyses. Thermal, electrochemical and morphological techniques were used to demonstrate the anticorrosive effectiveness of the standard epoxy resin (MP1) and its TiO2 composite (MP2). The effect of UV irradiation (for 2000 h), on the effectiveness of MP1 and its TiO2 composite (MP2), showed that TiO2 presence appreciably enhanced the protection efficiency effect of MP1.

The corrosion inhibition property of Gymneme Sylvestre on aluminum in an acidic medium has been investigated. The experimental techniques include potentiodynamic polarization studies, electrochemical studies, quantum chemical calculation and weight loss method. The results revealed that Gymneme Sylvestre acts as a potential corrosion inhibitor of aluminum in an acidic medium, showing 82% inhibition efficiency at 800 ppm concentration of it. Furthermore, the different thermodynamic parameters, including activation energy, Gibbs free energy and enthalpy have been calculated. The results showed that adsorption of the Gymneme Sylvestre molecule onto the aluminum coupon surface obeys Langmuir adsorption isotherm. The quantum chemical parameters were also calculated for major constituents of Gymneme Sylvestre.

Carbon steel corrosion inhibition in a hydrochloric acid solution by 2-[(5-methyl-isoxazol-3-yl)-methyl]-benzimidazole (MMB) has been studied by electrochemical techniques (PDP and EIS). Results showed that the inhibition efficiency increases with higher MMB concentration, and the maximum value of 86.6% was obtained at 10-3 M concentration. The prepared benzimidazole inhibitor showed higher inhibition efficiency upon raising the solution temperature from 303 to 333 K. Corrosion current density decreased from 660.9 µA cm-2 (blank) to 97.8 µA cm-2 (MMB) and charge transfer resistance increased from 20.2 Ω cm2 (blank) to 150.8 Ω cm2 (MMB). PDP studies showed that MMB is a mixed type inhibitor. The adsorption of this compound onto the carbon steel surface in a 1 M HCl solution followed the Langmuir adsorption isotherm, and the value of the standard free energy of adsorption ( ) is associated to physisorption and chemisorption.

This study investigated one of the chemical compounds taken by diabetic patients as a replacement for natural sugar. Its aim was to identify the electrochemical properties of sodium saccharin in different electrolytes, using a nano-sensor. Sodium saccharine was studied by cyclic voltammetric technique, in different electrolytes, using a modified glassy carbon electrode (GCE) with carbon nanotubes (CNT) as working electrode (CNT/GCE). It was found that the redox current peaks of 0.01 mM sodium saccharine in 1 M Na2SO3 enhanced both redox peaks with the CNT electro-catalyst on the GCE surface. Different concentrations, pH and scan rates of sodium saccharine in Na2SO3 have been studied. Also, the nano sensor showed good reliability and stability towards the chemical compounds in the cyclic voltammetric cell. Other electrochemical parameters were determined, such as the potential peak separation (Epa-Epc≈100 mV), the current ratio (Ipa/Ipc≈1) of the redox peaks and the cathodic-anodic reaction rate. The diffusion coefficient value was determined at different scan rates.

Environmental green compounds have emerged as powerful inhibitors for metals and alloys corrosion. So, this article attempts to show that barbituric (BA) and thiobarbituric acids (TBA) are good green corrosion inhibitors for copper immersed in 0.6 mol/L NaCl. A combination of quantitative and qualitative tools were used in this investigation, such as electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, FT-IR spectroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX). Polarization measurements indicate that these compounds can function as mixed type inhibitors. It was found that the adsorption of these inhibitors onto the copper surface obeyed Flory-Huggins isotherm. Also, the effect of temperature in the inhibitors absence and presence was studied according to Arrhenius isotherm. Some thermodynamic functions of dissolution and adsorption processes were calculated, such as activation energy (Ea), enthalpy (ΔH*), free energy (ΔGo) and entropy (ΔS*). The barbituric and thiobarbituric acids recorded high inhibition efficiency of copper corrosion at concentrations of 5x10-3 mol/L and 1x10-3 mol/L, respectively.