Portugaliae
Electrochimica Acta

Personal opinion of the author on the use of mercury and amalgam electrodes for determination of trace amounts of biologically active organic compounds is expressed. This view is supported by references to numerous reviews and original papers from UNESCO Laboratory of environmental electrochemistry supporting the claim that both mercury and amalgam electrodes can play useful role in modern practically oriented analytical laboratories.

The article deals with preparing of lithiated graphite material. The lithiated graphite material can be used as active electrode material in lithium-ion batteries. Most of the commercially produced lithium-ion batteries have the negative electrode based on graphite. The capacity losses which are caused by irreversible capacity of graphite may reduce the potential capacity of the battery from 15 % up to 45 %. These losses arise on negative electrode interphase (solid graphite electrode and liquid electrolyte), where during the formation process is created the SEI (Solid-Electrolyte Interphase) layer. The layer is composed from lithium atoms and the decomposition products of electrolyte solvents. The SEI layer is indispensable for correct function of lithium-ion battery. In this article are presented experimental methods for synthesis of lithiated graphite material. The article describes the three concepts of preparing lithiated material and its using like a precursor for preparing of negative electrode. The first method is based on using n-butyllithium (C4H9Li) reagent, its behaviour as the donor of lithium atoms, and graphite acts as the acceptor of lithium atoms. The second concept follows the first one only with adding an ionic compound to graphite, in our case FeCl3. The last concept presents the electroless lithiation process, which is based on different electrochemical potential between lithium and graphite.

The organic-inorganic hybrid sol-gel films, the structure of which comprises interconnected inorganic and organic networks have been reported as an environmentally friendly anti-corrosion pre-treatment for several metals, including aluminium alloys. In this paper, an epoxy-silica-zirconia hybrid sol-gel coating was synthesized from glycidoxypropyltrimethoxysilane (GPTMS) and zirconium n-propoxide (TPOZ) precursors and applied to EN AW-6063 alloy by dip-coating. To promote the organic network formation through the epoxy group polymerization at room temperature, two types of amine crosslinkers were added during synthesis: diethylenetriamine (DETA), in different concentrations, and a tri-functional amino-silane. The evolution of the curing process and the corrosion behaviour of the coated aluminium alloy specimens were evaluated by Electrochemical Impedance Spectroscopy (EIS) in 0.5 M NaCl. The morphology and surface chemistry of the hybrid coatings were characterized by Energy Dispersive Spectroscopy (EDS) coupled with Scanning Electron Microscopy (SEM) and by Fourier Transform Infrared Spectroscopy (FTIR). The results obtained revealed that the sol-gel coatings with lower amine ratios required longer curing times, but showed the best anticorrosive performance with time. The increase in amine concentration has led to a more cross linked organic network, resulting in higher initial coatings resistance; however it has turned coatings more hydrophilic, prone to rapid degradation in water.

The article deals with description of rheological and electrical properties of solvents for electrolytes of lithium-ion batteries. Solvents mixture of dimethyl sulfone and sulfolane at different volume ratios and with a lithium salt (LiClO4) appears as a potentially suitable electrolyte. In this work, we investigate the influence of different solvents and their mixtures in order to find a solvent which increases the fire safety of such battery. The aim of this experiment is to investigate the rheological properties, particularly density and dynamic viscosity of solvents with lithium salt in temperature dependence and to find the optimal composition of the electrolyte from the perspective of achieving the lowest dynamic viscosity and better electrical conductivity, because both quantities are closely related with Walden’s rule. The vibration method is used to determine the values of dynamic viscosity.

The aim of this study was to improve the properties of cathodic material for lithium-ion batteries based on LiCoO2. The solid phase reaction method was chosen as a manufacturing method of the doped base material. This method has already been tested for the production of basic material. Materials selected from the group of alkali metals were chosen as the doping elements. The main objective was to use these added elements for stabilizing the structure of the LiCoO2 material and for limiting the process of their degeneration.

This article highlights the fundamental role of mass-transport for interfacial reactions. First, the dissolution of particulate CaCO3 is discussed demonstrating how the dimensions of the dissolving particle can ‘switch’ the reaction mechanism from being diffusion to surface controlled. Second, the influence of mass-transoprt on electrochemical reactions is considered, specifically considering how electrode modification can alter the observed voltammetric response in the absence of changing the electrochemical mechanism or the rate of electron transfer. Finally, these observations on the chemically controlling role of mass-transport are concluded by considering nanoparticle toxicity and how ‘size effects’ may be exhibited even in the absence of altered thermodynamics or interfacial kinetics of the reactions involved.

This study describes the application of a Ti/Pt/PbO2 electrode as photoanode in the degradation of the dye Direct Red 80 (DR80). The electrode was prepared by platinization of a titanium substrate, followed by electrodeposition of a PbO2 layer. The presence of β-PbO2 phase was confirmed by X-ray diffraction. DR80 degradation tests were performed by different techniques, namely, photolysis, photocatalysis, electrocatalysis and photoelectrocatalysis. The best colour removals were obtained in the photoelectrocatalysis assays and were higher than 85% for 5.0 and 12.5 mg L-1 dye initial concentration and about 72% for 25.0 mg L-1 DR80 initial concentration, after applying a current intensity of 5 mA for 6 hours. At a DR80 initial concentration of 25.0 mg L-1, the best absorbance removals were obtained in the photoelectrocatalytic assays, with a current intensity of 50 mA, which led to a colour removal of 100% after 4 hours. Photolysis and photocatalysis presented similar colour removals that were 62, 26 and 18% for the initial concentrations of 5, 12.5 and 25 mg L-1, respectively.

The present work studies the behavior of hybrid sol-gel films based on tetraethyl orthosilicate (TEOS) and vinyltrimethylsiloxane (VTMS) precursors applied over commercial tinplate. In previous works VTMS films obtained by the sol-gel technology were tested to verify their good corrosion performance over short immersion times in a citric acid/sodium citrate buffer solution. However, at longer exposure times the high porosity inherent to organic sol-gel films allows the aggressive media to reach the metallic substrate and start the corrosion process. In order to overcome these limitations, hybrid organic-inorganic sol-gel coatings were obtained using the dip-coating method. This work also studies the influence of the ageing time of the hybrid sol-gel in the formation of a uniform and continuous film. The obtained layers were characterized using a Scanning Electron Microscopy (SEM) and mechanical profilometry. The corrosion performance in organic acid media was tested using polarization curves and Electrochemical Impedance Spectroscopy (EIS) with a 0.1M citric/citrate buffer solution as electrolyte. The results obtained suggest that a minimum ageing time of 10 days is needed to obtain uniform films. The electrochemical measurements indicate a clear improvement on the barrier properties on the hybrid sol-gel compared to the organic ones. A major decrease in the impedance values after 24 hours of immersion indicates that it is necessary to improve the long-term barrier properties to achieve an industrial application.

Corrosion of steel in concrete is one of the major causes of structure degradation, requiring expensive maintenance. The using of hot dip galvanized steel (HDGS) has been recognized as one effective measure to increase the service life of reinforced concrete structures in marine environmental. However, HDGS corrodes in contact with high alkaline environment of fresh concrete. Although this initial corrosion process allows the formation of a protecting layer barrier, the corrosion that occurs initially is harmful and chromate conversion layers are usually used to prevent it. Due to toxicity of Cr(VI), these kinds of pre-treatments have been forbidden and hybrid coatings have been proposed as alternatives [1-3]. To evaluate the performance of these coatings, beyond the laboratory characterization, in situ tests in real conditions should be performed. An electrochemical system to measure the macrocell current density (igal) was designed to evaluate the degradation of HDGS coated samples with different organic-inorganic hybrid films, embedded in mortar during 70 days, using an automatic data acquisition system. This system revealed to be feasible and highly sensitive to coatings degradation. Also, allow distinguishing different hybrid coatings with different thicknesses.

Mentha Spicata irrigated by wastewater from the city of Settat (Morocco) was tested as corrosion inhibitor of aluminum in 1 M HCl using polarization method and weight loss measurements. The inhibition efficiency of mentha spicata oil was calculated and compared. We note good agreement between these methods. The results obtained showed that the tested inhibitor reduces the kinetic process of corrosion of aluminum. Its efficiency increases with the concentration and attained 83,01% at 1800 ppm. The effect of temperature on the corrosion behaviour of aluminum in 1M HCl was also studied in the range 283 K and 313 K. The thermodynamic data of activation were determined. The analysis of mentha spicata oil obtained by hydro-distillation using gas chromatography (GC) showed that the major components are carvone 57.11 % and limonene 27.77%.

The anodic dissolution of zinc electrodes in sodium chloride aqueous solution has been investigated experimentally. The effects of application of polarity reversal (PR), ultrasonic (US) enhancement, stirring, current density (CD), concentration and pH of the supporting electrolyte, and temperature of the bath were studied. The results revealed that application of PR increased the dissolution of Zn but the current was low. However, the application of US enhancement led to higher zinc dissolution accompanied with higher current efficiency (CE). The combination of US enhancement and stirring led to more dissolution of zinc. Increasing the current density and concentration of NaCl increased the dissolution of zinc and the current efficiency was almost constant. On the other hand, pH of the bath did not play a significant effect on the amount of the dissolved zinc or current efficiency. It was also observed that increasing the temperature from 10 oC to 40 oC led to a significant increase in the mass of the dissolved zinc and CE; but the increase of temperature from 40 oC to 50 or 60 oC, however, did not have a significant effect.

The main objective of this work is to study the behavior of copper corrosion in nitric acid medium (2 M) for the evaluation and comparison of the corrosive power of the essential oil of Thymus Satureoides. To do this, we used weight loss and polarization techniques. The results show that the recovery rate of copper corrosion decreases in the presence of the essential oil tested. In a second step, we performed tests on the major component of the oil and the results obtained showed that the activity of the essential oil of thyme is clearly not related to it’s major constituent. On the other hand, it is clear from this study that the inhibition efficiency increases with the concentration of inhibitors to reach 89.04% at 1200 ppm for the essential oil of thyme and 69.72% at 1600 ppm for borneol. The adsorption isotherm and the activation energy were also determined.

A different approach for protecting the aluminium in 1M HCl is done by strengthening the surface oxide film of aluminium with nickel titanate particles. Weight loss methods, open circuit potential measurements and polarization techniques are used to measure the corrosion behaviour of aluminium samples. The corrosion rate of nickel titanate deposited aluminium shows lower values compared to pure aluminium in HCl medium. The intermixing of aluminium oxide with nickel titanate enhances the corrosion resistance property of the aluminium oxide layer on the surface of aluminium and thereby reduces the coulombic and non-coulombic loss of metal.

The ultrasonic measurements of solutions of uranyl caprylate and laurate in a mixture of 50/50 benzene-dimethylsulphoxide (V/V) have been used to determine the critical micellar concentration, ultrasonic velocity and various acoustic parameters at different temperatures. The results confirm that there is a significant interaction between uranyl soaps and the mixed organic solvent molecules.The values of critical micellar concentration of uranyl caprylate and laurate are in good agreement with those obtained from conductivity measurements.

The inhibition efficiency of sodium gluconate (SG)–Zn2+ system in controlling corrosion of carbon steel in sea water has been evaluated by weight-loss method. The formulation consisting of 250 ppm of SG and 75 ppm of Zn2+ has 98% IE. Influence of duration of immersion on the IE of SG-Zn2+ has been evaluated. The mechanistic aspects of corrosion inhibition have been investigated by polarization study and AC impedance spectra. The protective film has been analysed by FTIR and luminescence spectra. The surface morphology and the roughness of the metal surface have been analysed by atomic force microscopy. The protective film consists of Fe2+ - SG complex and Zn(OH)2. It is found to be UV – fluorescent.

Metal matrix composites are heterogeneous systems containing matrix and reinforcement. Their physical and mechanical properties can be tailored according to requirement. They are used in automobile, aircraft and marine industries because of their increased corrosion resistance. In this paper weight loss corrosion test, open circuit potential test and potentiostat test are conducted on AL6061/ Red Mud metal matrix composites in different concentrated neutral chloride solutions like sodium chloride solutions. Composites are prepared by liquid melt metallurgy technique using vortex method. Composites containing 2, 4 and 6 percent of red mud are prepared according to ASTM standards. Specimens are machined and made ready by standard metallographic methods. Weight loss corrosion studies, open circuit potential studies and potentiostat studies, are carried out in 0.035, 0.35 and 3.5% solutions of sodium chloride. The corrosion rate decreases with increase in the exposure time for all specimens in all corrodents in all the methods of testing. Corrosion rate also decreases with the increase in reinforcement content of the composites. Hence the composites can be used for the manufacture of the equipments used in marine environment so that they lost long.

Based on the energy form waste concepts we present here our results of the study of utilizing waste tea dust for preparing carbon, called the biocarbon. Tea dust after decocting has been selected as a low cost source of producing the carbon. Un-activated and activated carbons are produced by heating the tea waste around 250 oC for 2 h. For the first time, boric acid (H3BO3) has been reported through this work as a chemical agent for activating the selected biowaste. After physical characterization, the biocarbons have been tested in 3M KOH electrolyte solution for the possible application as electrodes in electrochemical double layer capacitors (EDLCs). Cyclic voltammetric studies with boric acid activated carbon of tea show slight improvement in the capacitance values over un-activated tea derived carbon. The study suggests that boric acid may be used as an activating agent for producing activated carbons.

The degradation of Acid Red I dye (ARI) and Luganil Blue N (LBN) has been studied by electrochemical treatment methods. The efficiency of cathode materials such as platinum, copper, zinc, lead, graphite, nickel, steel and titanium metals on the degradation of Luganil Blue N and Acid Red I dyes were investigated. The suitable cathode material was chosen and other parameters such as current density, and NaCl and dye concentrations were optimized. The electrolysis process was monitored by UV-Vis spectrophotometer and measuring chemical oxygen demand of the electrolyzed solutions. The overall COD removal efficiencies reached as high as 74.24% and 87% for ARI and LBN, respectively.

The chemical reaction of rhodamine B by electro-generated species using Pt and BDD electrodes was performed. The product(s) of this chemical reaction are related to the supporting electrolyte and electrolysis time. The rate of discoloration is affected by the current density, initial pH, temperature, and the nature of the supporting electrolyte. However, the initial dye concentration and the ionic strength did not show any significant effect on both electrodes. Discoloration of the dye and mineralization were not observed in presence of sulfate and nitrate with the Pt electrode, but occurred slowly with the BDD electrode. In the presence of KCl and KBr, the discoloration was very fast with both electrodes, and was accompanied with partial degradation. In the presence of KCl, the colorless rhodamine B solution turned rose after several hours of being set at rest.

The effect of synthesized 1,1'-propane-1,3-diylbis[3-(chloromethyl)-5-methyl-1H-pyrazole], dimethyl 1,1'-butane-1,4-diylbis(5-methyl-1H-pyrazole-3-carboxylate) and 1,1'-butane-1,4-diylbis[3-(chloromethyl)-5-methyl-1H-pyrazole] on corrosion of C38 steel in hydrochloric acid solution has been investigated in the temperature range from 298 K to 328 K by weight loss, potentiodynamic polarization method and modelled with an equivalent electric circuit. All the compounds exhibited more than 90% anticorrosion activity, the highest is 96 % by 1,1'-butane-1,4-diylbis[3-(chloromethyl)-5-methyl-1H-pyrazole], and it has been shown that the inhibition efficiencies increased with the concentration of the inhibitors, remaining almost constant in a wide temperature range. Potentiodynamic polarization studies suggested that it is a predominance cathodic type. Nyquist plots showed depressed semicircles with their centre below the real axis. The adsorption on the C38 steel surface followed the Langmuir adsorption isotherm. The thermodynamic parameters for dissolution were investigated at different concentrations and temperature. The theoretical study by modelling the molecules of these inhibitors has been performed by considering the Density Functional Theory (DFT) using the Gaussian 03W suite of programs that can calculate the different quantum parameters such as EHOMO, ELUMO, ΔEHOMO, ELUMO, and µ dipolar moment, allowing us to confirm the results found by the gravimetric and electrochemical methods.