Portugaliae
Electrochimica Acta

Microelectrodes have recently been applied in several areas of electrochemistry. Some of their most relevant -properties will be described and an overview of the most important applications during the last few years will be given. These include kinetic studies under steady state and non-steady state conditions3 electrochemical studies without supporting electrolyte and in highly resistive media and electrochemical nucleation studies.

The ionic conductivity and the complex permittivity έ ' of a crystal of RbAg4I5 was calculated from measurements in the range of 27 to 39 GHz. The crystal was prepared from RbI and AgI, and tested by DC conductivity measurements. The conductivity is found to be constant in that microwave range, in contrast to what is observed in crystals such as a-AgI, a-CuI and 3-CuBr, where a diffusion mechanism intermediate between the jump diffusion and the single diffusion in liquids has been proposed. Therefore, elementary steps of translational diffusion occur in a time scale faster than in the above other materials: the moving Ag+ ion will go with less friction. The complex permittivity of RbAg4I5 has also been measured. Keywords: diffusion; jump-diffusion; ionic conductivity; permittivity; microwave technique; soli d electrolytes; complex conductivity; rubidium silver iodine.

This paper describes results obtained with an AISI 304 stainless steel in 1 M HCl and 1 M KCl solutions, with the aim of contributing to the understanding of the processes occurring within growing pits. The kinetics of dissolution were studied at constant potential by the scratch method. In 1 M HCl a salt film formed below the passivation peak and its rate of formation increased as the applied potential was made more noble. In 1 M KCl the rate of film formation was not affected by potential. In this solution a passivating film developed even before the current maximum in the anodic polarization curve. Since the solutions found within growing pits usually have low pH and high chloride concentrations it is concluded that, as pits develop, their surface should become covered by salts layers of increasing thickness. Key Words: dissolution kinetics, pitting and stainless steel.

Electrode kinetic parameters, p and k, the charge transfer coefficient and the conditional charge transfer rate constant, respectively, for the anodic dissolution of copper, cobalt, zinc and bismuth have been calculated from voltammetric scans carried out in solutions containing a selected supporting electrolyte and the same supporting electrolyte plus EDTA, respectively. The values found for the parameters in both media showed that they are affected by the presence of the complexing agent  was found to be related to the conditional formation constant, of the metal-EDTA complex studied and the k0/k0EDTA ratios obtained evidenced adsorption of the metal-EDTA compound on the electrode surface for all the cases but bismuth; its extent being closely related to the metal transition character of the metal ion involved in the complex. Keywords: Electrode kinetic parameters; anodic dissolution of pure metals; arbitrary current method.