Portugaliae
Electrochimica Acta

Voltammetric studies on copper, nickel and cupronickel alloys of various compositions in neutral chloride solutions revealed that the passivation is due to the formation of duplex film consisting of inner compact Cu2O layer with outer chloro hydroxy layer. Under transient cyclic polarisation conditions, the presence of nickel hindered the passive film formation decreasing its thickness and ohmic conductivity. The reduction of these passive films to copper was markedly favoured by chloride ions. The presence of nickel in the alloy hindered the reduction of these passive films.

In this paper we discuss the advantages of using interactive simulation programmes for electrochemical dynamical experiments to help both researchers and students in understanding the phenomena underlying these experiments, as well as in obtaining meaningful chemical and electrochemical parameters associated with the redox transformation mechanisms. A PC computer programme developed for this purpose, and which is available to anyone interested, is also presented and applied to the demonstration of virtual cyclic voltammetry.

Porous unsupported Pt-Ru single phase alloy electrodes with different compositions viz., 9:1, 7:3 and 5:5 are prepared by NaBFL reduction method at room temperature. The reactivity of these alloy electrodes towards the methanol oxidation reaction (MOR) is systematically investigated in different electrolytes of high and low pH with various quantities of methanol at room temperature by using cyclic voltammetric (CV) and steady-state galvanostatic polarisation techniques. Various electrochemical processes occurring in different potential regions are discussed. The highest activity of the MOR is obtained for a 7:3 electrode in 2.5 M H2S04 / 2.5 M CH3OH and in 6 M KOH / 6 M CH3OH mixtures, respectively. It is concluded that by choosing the proper ratio of OH ions and CH3OH in solution, it is possible to remove completely the intermediate organic species and/or poisonous species that retard the MOR.

Four complexes of 2,2'-bi-4,5-dihydrothiazine (btz) with Co(II), Ni(II), Mn(II) and Cu(II), and two complexes of 2,2'-bi-thiazoline (bt) with Co(II) were synthesized and characterized, three of them, the Mn(II) complex and the two bt complexes, for the first time. These six complexes were studied using cyclic voltammetry in acetonitrile solution.All displayed reversible or quasi-reversible behaviour, and two waves were observed in the case of [Co(btz)3] [C104]2- All the results are described and discussed.

The oxide films formed by potential cycling on commercial Ti6A14V alloy, that has been surface implanted with iridium, are studied by capacitance measurements and Auger analysis. It is observed that these films become enriched in iridium when etched in sulphuric acid solution prior to their formation, simultaneously with a change in the type of semiconductivity (n-type to p-type).

An outline of a document with a basic vocabulary used in electrochemical industries is indicated following an historical development with references to sources where it would be properly explained. The objective would be to avoid having to include "definitions" on elementary concepts in CEN and ISO standards. The inadequacy of those definitions in standards is indicated and the present approach is justified.

The quantity pH=lg aH is immeasurable, as it involves a single ion activity. The IUPAC recommendations for the pH scale for aqueous solutions are based on the Bates-Guggenheim convention for the calculation of the chloride ion activity coefficient. The idea of this convention, intended to be applied to ionic strength not higher than 0.1 mol kg"1, was to impart pH with as much fundamental meaning as possible while recognising that it is conventionally based. The Pitzer theory, involving ionic specific interactions, may be applied in the calculation of single ion activity coefficients at ionic strengths higher than 0.1 mol kg"1. This approach has the merit that all possible known buffers, with or without background electrolyte, and those yet to be developed, can be assigned pH values.

The effect of 4(2-pyridyl)-l-benzaldehyde-3-thiosemicarbazone derivatives towards the corrosion of iron in 1M HC1 solution at 303K was investigated. Potentiodynamic and weight loss measurements show that compounds under investigation act as effective inhibitors for the corrosion of iron in 1 M HC1. The results show that these compounds behave as mixed type inhibitors. The corrosion rate was found to be a function of the nature and concentration of the inhibitors. The adsorption of the compounds on the iron surface is found to obey Temkin's adsorption isotherm.

The electrokinetic behaviour of aqueous suspensions of naturally occurring clays with different mineralogical composition is reported as a function of pH and electrolyte concentration. The results indicate that the clay particles carry a net negative charge in the examined pH range. The estimated zeta (Q potential values have been interpreted in terms of the composition and structural characteristics of the clay minerals, nature and charge of the particle surfaces and properties of the electric double layers developed at the clay/electrolyte solution interface. The  potential values of the clays obtained using microelectrophoresis and electroosmosis techniques have also been compared.

Justifica-se a necessidade de compreender bem os fundamentos da electroquímica para entender e consequentemente resolver adequadamente os problemas da protecção contra a corrosão.

The potentialities and limitations of electrochemical methods in the study of trace metal speciation in natural waters will be focused, as well as the factors influencing the voltammetric signal, with a special emphasis on the diffusion coefficient of labile macromolecular systems. Some applications of voltammetric techniques to the speciation of trace metals in natural samples are presented, namely with humic matter, estuary and seawaters.

A procedure for the quantitative analysis of mixtures of acids, based in the treatment of data of potentiometric pH titrations by multivariate chemometric calibration methods, is presented. Experimentally, the procedure consists in the titration of a set of mixtures of acids similar to the sample, but with known concentration of the components, which constitute the calibration set. A two step data analysis procedure is used for the development of calibration models: (i) the raw titration curves are adjusted to a polynomial equation of the fifth degree and the inverted titration curves are obtained (volume as function of the pH); (ii) the inverted titration curves are used to develop calibration models, using multivariate chemometric methods like partial least squares and artificial neural networks which can deal with some non-linearity in the basic inverted model. The results showed that adequate predictions of the concentration of the acids of the mixture are obtained.

The incorporation of metals in organic conducting polymers by electroless deposition is demonstrated for Ni-P on electropolymerized polyaniline films. The creation of starting catalytic conditions for effective nickel electroless deposition is discussed and the influence of the electropolymerization conditions on the metal particles dispersion is analysed. Nickel electroless deposition has been carried out on polymer films built up to various thicknesses in order to produce several metallic contents and / or different sized Ni-P particles. The so-obtained modified electrodes have been characterised including its redox behaviour.

The electrochemical behaviour of Vitamin BI2 derivatives with cobalt (III) complex and containing an alkyl chain with a peripherical pyrrole group is analysed by cyclic voltammetry. Adsorption of the derivatives under oxidised and reduced forms appears to allow the oxidation of the pyrrole group with concomitant polymer film formation. The length of the alkyl chain has been seen to play an important role on the polymer properties namely on its conductivity and thus on the possibility of thickening the film. Although a relatively high potential is required for the adequate monomer oxidation the electropolymerization of these new monomers can be envisaged for modified electrodes preparation.

Estudou-se a influência do ião Fe2' na biocorrosão de um aço macio, na presença e na ausência de bactérias redutoras de sulfato (SRB). Os estudos foram realizados por voltametria cíclica, curvas de polarização de estado quasi-estacionário e perda de massa. Os resultados indicaram que o aço é mais susceptível à corrosão quando o ião Fe2+ está presente no meio.

The performance of an ion selective electrode array (ISEAR), designed for the determination of benzoate in the presence of iodide, constituted by all-solid-state electrodes with Aliquat 336 S or tetraocrylammonium salts immobilised in PVC membranes, is described. The response of the ISEAR to both ions was obtained by two treatments: (i) calculation by non-linear least squares (NLS) of the parameters of a model based on the Nikolskii-Eisenmann equation; and (ii) principal components regression (PCR). The results are compared and discussed. Results obtained in the determination of benzoate in pharmaceutical formulations containing iodide are included.

This session intends to celebrate the 5t n anniversary of the Portuguese Electrochemical Society by presenting an account on the establishment of the electrochemistry as a science and on its development at the Portuguese Universities, as well as a reference on the role of that society on the evolution of this science within the Portuguese scientific community. The former aspects will be presented by the invited speakers, whereas the latter are considered now, in the opening of the session.