Portugaliae
Electrochimica Acta

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.