Portugaliae
Electrochimica Acta

It was developed and validated an analytical methodology able to quantify aluminium in haemodialysis fluids, based on the reaction of aluminium with cupferrron (ammonium salt of N-nitroso phenyl hydroxyl amina), on the adsorption of the complex on a hanging drop mercury electrode, and on the measurement of the reduction current of the complex. Parameter validation was done using square wave voltammetry for accumulation potential, time of accumulation, frequency, pulse amplitude, equilibrium time, cupferron concentration, optimum pH. Performance parameters of the method were established: detection limit, quantification limit, reliability, lineal interval for the calibration curves. The method was applied to haemodialysis mineralized fluids, being done the quantification of the aluminium presented.

In the present paper we have carried out a study in order to determine the grade of corrosion affectation in concrete structures reinforced by the incorporation of additives, using electrochemical techniques and analyzing the respective effect on their mechanical properties. Quantitative and qualitative determination of their properties has been done (chemical analysis of the additives and steel, resistance to the compression, and flexural strength, porosity, and water permeability). The methodology was carried out according to ASTM standards and the action of the admixtures was evaluated using corrosion potentials and corrosion rates. The carbonatation and penetration of chlorides were also determined. The study was supplemented with a morphologic characterization by means of a scanning electron microscope. Specimens with and without reinforcement were elaborated, three of each being tested in order to obtain an average. Prismatic specimens without reinforcement were also casted with the following chemical additives: air-entraining, plasticizers, retardants, accelerating, coloring and fly ash. After curing, they were exposed to an aggressive atmosphere with sodium chloride. The general performance of the specimens after the period of exposition is good, since practically all of them developed very low corrosion rates, between 0.55 × 10-4 and 4.76 × 10-4 mA/cm2.

The objective of this paper is the establishment of the better instrumental conditions of analysis for the determination and quantification of mercury in environmental samples by potentiometric stripping analysis. This determination is based in the deposition of mercury into a thin gold film, previously deposited onto a glassy carbon electrode, and then stripped back to the work solution by means of an added oxidant agent. We carried out tests to determine the oxidant concentration, electrolysis potential, support electrolyte and its concentration, potassium chloride concentration and the detection / quantification limits, having in mind to determine in a precise, reliable and reproducible form the presence of mercury, its further quantification, previous mineralization by microwave digestion and its preconcentration by cation exchange column chromatography, to eliminate interferences from metallic ions. The quantification was carried out by the standard additions method. This work shows a detection limit of 5 μg/L and quantification limit of 17 μg/L.

It was developed a sensitive analytical methodology to determine iron in water samples and other matrixes. It was used a differential pulse cathodic stripping voltammetry technique and adsorptive preconcentration with KSCN as a ligand and NaNO2 as a catalytic agent. The methodology has a linear range between 0.7 mg/L and 10.0 mg/L, a detection limit of 0.2 mg/L and a quantification limit of 0.7 mg/L. The averaged sensitivity is 344 nA/(mg/L). The accuracy has a recovery of 102% for 1.0 mg/L of iron with a variation coefficient of 4%. Also it was studied the linearity of the Fe-cathecol system, which has an average sensitivity of 4 nA/(mg/L), much lower than the one of the Fe-KSCN system, and a wider linear range from 2.4 mg/L to 50.0 mg/, a detection limit of 0.7 mg/L and quantification limit of 2.4 mg/L, with a variation coefficient of 8% and recoveries near 100% at different concentration levels.

To evaluate the electrochemical parameters of the reinforced concrete specimens at laboratory level there is no problem at all, because one can use any well-known electrochemical technique, but in site monitoring, there are few techniques being able to obtain these parameters. In this work a viable alternative is presented for the electrochemical evaluation of the reinforced concrete specimens in laboratory or in site monitoring. In order to have a reference of the corrosion rate obtained with the electrochemical noise technique and to be able to establish if these are real ones, measurements with commercial equipment were made applying the polarization resistance technique.

This work is part of the DURACON project, in which it is characterized the concretes exposed durability in the present iberoamerican environmental conditions, being based in the exhibition of armed specimens in at least two different atmospheres, a marine and an urban, in each iberoamerican participant country. The results obtained by exposing these armed concrete specimens to the environmental conditions of the city Chihuahua, Mexico, during the first 15 months of exhibition, will be discussed in this work. Two concretes were designed, one with a relationship w/c (water/cement) = 0.65, and the other one with w/c = 0.45, and three cover thickness (1.5, 2.0 and 3.0 cm). Tests were mainly based in measuring electrochemical parameters that allowed evaluating the corrosion kinetics of the bars, by means of potential corrosion measurements and implementing the technique of linear resistance polarization in order to determine the corrosion rate. All this information will permit, with the use of specific models, to design durable concrete structures, and to repair appropriately those already existent, what will rebound in a decrease of the economic losses that at the moment is causing the phenomenon of corrosion in our country.

The present work shows the results of the electrochemical evaluation of reinforced concrete specimens exposed in 3 to 5% Na2SO4 solutions during four months exhibition. The concrete was elaborated with water/cement ratio (w/c) of 0.4, 0.5 and 0.6. The electrochemical evaluation was carried out using the lineal resistance polarization technique. The results of these tests show that the biggest attack for Na2SO4 was presented in the specimens of 0.5 and 0.6 w/c ratio. Also, they showed a passive tendency after curing. On the other hand the Rp curves analysis, shows that in all the evaluated specimens a great corrosion rate was presented during the curing stage and after some time the system tends to be stabilized approximately in 0.05 mm/yr.

This research was made to determine the corrosion rate of the copper cable used in grounding and lightning systems, at the electrical generation plants from the Costarrican Electrical Institute. The methods used were linear polarization resistance (LPR), and the weight loss one. This report includes both, laboratory and field tests of corrosion rates, using as electrolytes two products commercially available. Moreover, some electrochemical experiments were developed at the laboratory, in order to know the reaction mechanisms. The goal of this study was to generate criteria for the maintenance and/or the substitution of copper cables according to their deterioration. The results showed that the corrosion rate in "A" is at least ten times higher than in "B". In addition, several samples in the "A" electrolyte had pitting corrosion. The study indicates that from the point of view of the corrosion it is preferable to use product "B" like filling, since the generalized corrosion of copper is lower and in addition localized damage does not appear.

Methanol electrooxidation was investigated on tailored Pt-Ru-polyaniline catalysts prepared applying dynamic potential routines. The electrodes characterized by SEM, EDX and TEM present a uniform distribution of metal particles about 100 nm in size, composed of Ru and Pt on the fibrous polymer matrix. The effect of concentration in the range 0.05-1 M and temperature in the range 20 to 60 ºC on the methanol electrooxidation rate was determined. The apparent activation energy depends on the catalyst Ru content.

Carbon pencil electrodes are proposed as supporting material for the fabrication of disposable devices through surface modification by bismuth plating and polyaniline formation. The surface characteristics were assessed by fractal analysis under semi-infinite linear diffusion employing a soluble molecular probe, and scanning electron microscopic analysis. The results indicate that the surface topography for bismuth-modified electrodes corresponds to a 2-dimensional smooth surface, while for polyaniline-modified electrodes, a surface fractal dimension of 2.76 was obtained. These topographic characteristics indicate that bismuth-modified carbon electrodes are suitable for anodic stripping analysis, and polyaniline ones, due to the surface irregularities, may result a good supporting material for biomolecules attachment.

An integral analysis was carried out on the results obtained in laboratory experiments on electro-remediation of soils using two heavy metal-contaminated volcanic soils from the region of Antioquia, Colombia. Measurements of pH, conductivity, and pollutant concentration were made on each soil. The results were related to the structural characteristics of the soils employed in the experiments. Under the present experimental conditions it was shown that the soil with the lower concentration of organic matter had a lower pH regulatory capacity, that treatment without using wash solutions was more efficient for the mobilization of the metals, and that the particular characteristics of each soil conditioned the efficiency of the treatment.

Studies of soil resistance suggest that this type of measurement when carried out simultaneously with decontamination treatment, serves as a rapid method for analyzing the behavior of different soils under study, especially when an electric field is not applied.The variation observed in the first step of electro-remediation is related to the ionic content of the segments adjacent to the electrodes. The use of a wash flow facilitates the formation of "ionic batches" near the electrodes. The soil with the higher content of organic material shows lower resistance in the first stage of the treatment. Measuring the electrolysis current without the use of wash flow, together with the other experimental parameters, allows the evaluation of the soil characteristics in experiments of relatively short duration.

The electropolymerization of phenylacetylene on a Pt electrode has been carried out in two different solvents, acetonitryle and propylene carbonate. The kinetic study carried out leads to values in the kinetic parameters which are significantly different in both solvents. The values deduced for na, Z (reaction order with respect to the phenylacetylene concentration) and activation enthalpy and entropy, were 0.75, 1, 25.3 kJ mol-1 and -87.0 J mol-1 K-1, respectively, in acetonitrile, and 0.25, 0.5, 33.6 kJ mol-1 and -105 J mol-1 K-1, when working in propylene carbonate. The discrepancy in the values can be explained as a consequence of the change in the initiation step of the polymerisation induced by the adsorption of the acetonitryle molecules. The product obtained was isolated, purified and characterised to be formed by a polyenic chain with a linear trans structure. The average molar mass of the product was 3095, corresponding to a polymer formed from around 30 units of monomer.

A few non-aqueous dipolar aprotic solvents of medium to high permittivities, low viscosities and large temperature intervals between freezing and boiling points have been used to prepare electrolyte solutions applicable to primary and rechargeable high energy batteries. Lithium perchlorate is a salt often chosen to obtain those systems. In this work low temperature effects on conductivities and association constants of LiClO4 and Et4NBr in six different solvents have been analyzed, using the tetraethylammonium bromide salt for comparative reasons. The temperature interval was -30 ºC to 10 ºC. A few thermodynamic functions resulting from KA, T variations were determined being the results discussed on this basis. The accuracy and precision of results are high; whenever possible they are compared with others previously published.

Os estudos cronoamperométricos foram motivados pela observação de histerese de corrente nos perfis de redução dos voltamogramas realizados no sistema Sn/bicarnonato, já que é sabido na literatura que a presença de histerese é considerada indicativo de ocorrência de processos de nucleação. A ocorrência de nucleação foi verificada mediante técnica cronoamperométrica quando filmes eletrogerados na região de passivação são reduzidos. Empregando rotinas de análise de mínimos quadrados não lineares, foi obtido o ajuste entre os resultados experimentais e os calculados usando modelos teóricos que descrevem a nucleação eletroquímica. Assim, a eletrorredução do filme formado no extremo inferior da região estudada, pode ser explicada em termos de difusão e nucleação progressiva e crescimento 3-D controlado por transferência de carga. Por outro lado, a redução do filme electrogerado no extremo superior segue o modelo de nucleação progressiva e crescimento 3-D controlado por transferência de carga, com a presença de tempo de indução. A análise da variação dos parâmetros modelísticos com o tamanho do degrau de potencial permitiu estabelecer a influência dos valores das constantes de velocidade paralela e perpendicular à superfície para cada caso experimental.

The effect of the presence of CO2 and H2S in the well water used in the petroleum plant on corrosion of carbon steel has been tested using impedance measurements. Carbon dioxide leads to decrease in the resistivity of the film developed on the metallic surface, while the effect of hydrogen sulfide is less pronounced. Scanning electron micrographs have shown that corrosion products cover only small part of metallic surface in water containing CO2. Studies under polarization conditions will allow concluding that the dissolved gases in the well water reduce the ability of the film to protect the metal against corrosion. The influence of the oxoanions and halide ions on the corrosion rate of steel has also been analyzed.

The effect of iodide ions on the corrosion inhibition of mild steel in 0.5 M sulfuric acid in the presence of poly(4-vinylpyridine) (p4vp) was studied by weight loss and different electrochemical techniques such as electrochemical impedance spectroscopy, potentiodynamic polarization and polarization resistance measurements. The obtained results showed that poly(4-vinylpyridine) effectively reduces the corrosion rate of mild steel. The addition of potassium iodide (KI) enhanced the inhibition efficiency (P%). The synergism parameter (Sp) calculated from inhibition efficiency was found to be greater than unity, suggesting that the phenomenon of synergism exists between P4VP and iodide ions. The adsorption of p4vp alone and in combination with KI followed Frumkin adsorption isotherm. The effect of temperature indicated that the inhibition efficiency of p4vp decreases with increasing temperature. Study of temperature effect showed also that inhibition efficiency of (P4VP + KI) does not depend on temperature. The apparent activation energies in the absence and in the presence of P4Vp and ( P4VP + KI ) were determined.