Portugaliae
Electrochimica Acta

The electropolymerization of substituted manganese and iron metalloporphyrins with two pyrrole groups bonded in lateral chains is investigated. It is shown that under potentiodynamic conditions the film formation can be successfully achieved. A methodology for the polymerization of the iron containing monomer on microelectrodes is also presented. The behaviour of the polymer modified electrodes is studied for the O2 reduction, as well as for the oxygen and hydrogen evolution reactions, revealing good electrocatalytic activity.

Al 6061 powder and F800 grade SiC particles (SiCp) were used as raw materials for the preparation of metal matrix composites (MMC), via a powder metallurgy route (PM), with 0% to 20 wt % of SiCp, the reinforcement material. Corrosion studies revealed a linear dependency of the pitting potential (Ep) with the logarithm of the concentration of NaCl with a slope of ~-90 mV/decade, but there was no significant difference in the Ep values of the composite materials as a function of the concentration of reinforcement. Corrosion protection of PM Al SiC alloys was achieved by favouring the formation of a Ce/Mo-based conversion coating on the surface without the use of external polarisation. Pitting potentials were assessed in a 0.1 M NaCl solution after treatment. No increase in current density was evident for samples treated at pH 4.4 followed by post-treatment at 60°C for one hour, when polarised up to 0 mV (SCE). The role of Ce and Mo as inhibitors is analysed and discussed in terms of the protective character of the produced cerium-molybdenum conversion coatings.

Propylene carbonate (PC) and y-butyrolactone (GBL) are important dipolar approtic solvents used to prepare non-aqueous electrolytes for high energy lithium batteries [1-4]. A few salts have been tried in these solvents because they permit to work at lower and higher temperatures than the melting and boiling points of water respectively. Actually these solvents have much larger liquid temperature intervals than water and they are generally very stable and safe as it was demonstrated by Kita and Hasegawa in recent papers [5,6]. In this paper conductivity determination of lithium perchlorate (LiC104) as well as of tetra-ethylammonium bromide (Et4NBr) solutions in those two solvents have been obtained under different pressures. The resulting volumes of activation are positive for both salts and generally decrease as pressure increases for lower concentrations. The contrary is observed for higher concentrated solutions. The association equilibrium constants were also determined and they are almost constant or slightly decrease with pressure and decrease with concentration. All the experiments were carried out at 25 ºC ± 0.01 ºC.

The pitting corrosion of Aluminium was studied in 0.1 M halide solutions in various concentrations of decyl and dodecyl sodium sulphate. The results obtained from the potentiodynamic measurement show that the pitting corrosion is inhibited by the presence of organic compounds in this medium. The percentage inhibition was found to increase with increasing the concentration of the organic compounds in the medium at constant halide concentration. For solutions of constant halide concentration, the pitting potential varies with the logarithm of the inhibitor concentration according to a linear relationship. These results are interpreted in terms of competitive adsorption between halide ions and organic anions at the passive metal-solution interface. It was found that the efficiency of inhibition for a given halide concentration decreases in the order of dodecyl sodium sulphate > decyl sodium sulphate. At constant inhibitor concentration, the pitting corrosion was found to decrease in the order: CI- > Br- > I-.

Corrosion inhibition by some 4-phenylthiosemicarbazone derivatives with respect to the dissolution of copper in 2M HNO3 was measured using electrochemical techniques. Polarization curves indicated that these compounds act as mixed-type inhibitors, i.e. both the cathodic and anodic curves are affected. The observed effect follows the Temkin adsorption isotherm. The effect of the different structural features of these compounds on their inhibition efficiency has been studied. Results indicate that the rate of corrosion of copper increases with increasing temperature over the range 30-60°C both in the absence and in the presence of inhibitors. Some thermodynamic functions were also computed and are discussed.

In this work the polymer 4-pyridilmethylchitosan/Ru(EDTA) ([Ru(EDTA)(4PMC)]) was used as modifier in the preparation of chemically modified carbon paste electrodes. The electrochemical behavior of the polymer compound is governed by the a conversion of the monossubstituted species for disubstituted species when the reduction of Ru(III) to Ru(II) occurs. The cyclic voltammogram of the electrode prepared with the [Ru(EDTA)(4PMC)] in the presence of ascorbic acid presented an increment in the anodic peak current in 0,38 V, which indicates that the catalysis of ascorbic acid oxidation is mediated by polymer.