Portugaliae
Electrochimica Acta

The present work is a study on the electrodeposition of Copper on Zamak 5 from alkaline copper solution. The effects of time and current density on thick and cathodic current efficiency have been studied by gravimetric methods.

The corrosion of M2 high speed steel in aqueous media containing chloride, bromide, iodide, nitrate, sulphate and perchlorate salts of sodium and potassium of varying concentration has been studied using corrosion potential measurements, voltammetric and electrochemical impedance techniques. The influence of the cation was found to be small and an order of anion aggressiveness was established as: sulphate > chloride > bromide > perchlorate > iodide > nitrate.

Influence of the composition of molten mixtures Me2R04-Me2R207- U02R04 (Me = Li, Na, K, Cs; R = S, Mo, W) and of the main potentiostatic electrolysis parameters on the chemical, phase composition of cathode deposits and on their current efficiencies have been studied. Experiments were carried out at temperatures of up to 900°C in the air. It has been showed that uranyl-containing oxide salt melts with various cationic and anionic composition can be used for electrochemical obtaining of granular uranium oxides with the 0 / U atomic ratio ranging from 2.014 to 2.667.

Potentiometric measurements have been performed, at 25 °C, in cells of the type: Reference electrode 10mol/dm-3 KCl x g d m albumin (20

The functioning of a DNA-modified glassy carbon electrode was evaluated using the electrochemical system ferricyanide/ferricyanide, after different electrode conditioning in the absence or presence of the free bases adenine and guanine, and at different applied potentials. The results were compared with those obtained at the bare glassy carbon electrode

Square wave voltammetry at microdisk gold electrodes modified with a mercury film was used to quantify nickel levels in kidney samples of mice previously treated with a solution containing those species. Comparison of the results obtained by electrochemical techniques and atomic absorption spectrometry indicates that microelectrodes are a reliable quantitative technique and greatly enhances the working conditions.

Conventional gold electrode, gold, and mercury coated microelectrodes were used to study the electrochemical behaviour of iron species in osteoblast-like cell cultures medium. Gold microelectrodes, with or without surface modification, have shown to be useful tools for in vitro qualitative and quantitative analysis of iron ions released from stainless steel in biological systems.

The influence of the temperature and the electrolyte concentration on an alkaline Fuel Cell has been studied through the variation of the current density and the potential of the cell. As anode has been utilized a palladium membrane and as cathode, a carbon-tetrafluoroethylene-perovskit porous electrode. The electrolyte used is aqueous KOH.

In this work, an UV-vis spectrophotometer technique adapted to "in-situ" absorption-reflection experiments is presented. Visible spectra at different oxidation potentials for Polypyrrole/Polyvinylsulphonate composite controlled in 0.1 M LÍCIO4 water solution were performed. The evolution of the visible-absorption spectra in the oxidized and reduced states as a function of the number of cycles of the coloration/decoloration was followed.

A bilayer structure polypyrrole-flexible and inactive polymer has been constructed to transform molecular strain in macroscopic movement during electrochemical oxidation/reduction process of polypyrrole film. With the aim of optimizing bilayer movement, the rate (rad.s-1) of those electrochemomechanical movements for a same described angle (90°), the consumed electrical charge (mC) and electrical energy (mJ) under different electrical conditions and with different bilayer dimensions has been studied. The obtained results shown an increasing of both movement rate and consumed electrical energy per mass unit at increasing applied current per mass unit (mA.mg-1). Hower the electrical charge consumed remain constant. Also the bilayer dimensions have not influence on movement rate and on consumed electrical charge or energy per mass unit. However, for a constant consumed electrical charge per mass unit the angle traveled remains constant varying bilayer dimensions.

Square wave stripping voltammetry at wall-jet mercury thin film electrodes in continuous flow has been investigated, with particular attention to the anodic stripping voltammetry of zinc, cadmium, lead and copper, and the adsorptive stripping voltammetry of cobalt and nickel via the formation of complexes with nioxime ligand. Advantages of square wave voltammetry with respect to differential pulse voltammetry in the determination step and to batch determination without continuous flow are demonstrated. Nanomolar detection limits are found. Optimisation of experimental procedures is discussed.

The electrochemical reduction of fluoxetine was studied using a hanging mercury drop electrode in different buffer solutions up to pH 13 and with concentrations of fluoxetine varying from 1.0xl0"6M to 5.0x10"5 M_- A very strong adsorption of fluoxetine on the electrode was observed and the shape of the cyclic voltammograms suggests that in these conditions it corresponds to a quasi-reversible system for adsorbed species. The results obtained for the electrochemical quantification of fluoxetine in five pharmacological formulations existing in the Portuguese market were compared.

Thiourea is a promising non-cyanide lixiviant for gold hydrometallurgy. However, its high consumption due to degradation has hindered thiourea from commercial application. Thiourea oxidation is discussed and the role of sodium sulphite as a reductant in controlling the degradation of thiourea is investigated.

The electrochemical reactions of 0.01 M CH3CH2OH and 0.01 M HCOOH on platinum in 0.1 M HC104 were studied by means of Differential Electrochemical Mass Spectrometry (DEMS). Ethanol can be oxidized to C02 and ethanol, whereas formic acid produces only C02. Electroreduction products (ethane and methane) were observed only for ethanol. The competition reactions between ethanol and formic acid were studied when both compounds are present simultaneously in the bulk of the solution (0.01 M CH3CH2OH + 0.01 M HCOOH). Using isotope labelled H13COOH it was possible to distinguish the contribution of ethanol and formic acid: formic acid oxidizes to i3C02 (m/z = 45) whereas ethanol produces 12C02 (m/z = 44). It was observed that the reactivity of ethanol is similar to that found without formic acid in the solution, whereas the production of C02 from formic acid was diminished about 50%.

Electro-oxidation and electroreduction reactions of acetylene adsorbates on gold were studied in 0.1 M HC104. It was found that acetylene forms chemisorbates in a wide potential range. On-line electrochemical mass spectrometry (DEMS) was used for the detection of the reaction products on porous polycrystalline gold electrodes. Only C02 was detected during the oxidation of the adsorbates, whereas acetylene and ethylene were identified as products of adsorbates reduction. The oxidation and reduction of the chemisorbates on single crystal faces display distinctive differences. The oxidation charge (Qox) required to oxidize acetylene adsorbed species completely to C02 depends on the adsorption potential (Uad). The shape of the curve Qox vs Uad is also affected by the structure of the gold surface.

In this work, Ni-P and Ni-P-Teflon electroless thin films were optically characterized by ellipsometry. The measured ellipsometric angles A and ¥ are used to calculate the dielectric constant spectra of these materials. Effective medium theories (Bruggeman and Maxwell-Garnett) have been employed to determine the quantity of Teflon particles in Ni-P-Teflon systems. To complement ellipsometric data, SEM/EDS and SIMS analysis have been used as well as AFM imaging.