Portugaliae
Electrochimica Acta

The electrode processes of Neutral Red (3-amine- 7-dimethylamine-2-methyl-phenazine) have been studied voltammetrically on Glassy Carbon (GC) and on Indium Tin Oxide (ITO) electrodes in buffered aqueous solutions. Multicycle voltammetric treatment of neutral red yields a water insoluble surface film.

Magnesium, one of the lightest nonferrous metals assumes great importance due to many attractive structural, chemical and electrochemical features. The influence of the halide ions at concentrations ranging from 0.1 M to 2.0 M on the corrosion behaviour of primary magnesium has been investigated by galvanostatic polarisation and atomic absorption spectroscopy (AAS). The corrosion kinetic parameters namely open circuit potential (OCP), corrosion potential (Ecorr), corrosion current (Icorr) and Tafel constants (ba and bc) have been calculated from polarisation experiments. These data are interpreted to bring out the effects of the halide ions and their concentration on the corrosion of magnesium in these media. The amount of magnesium anode dissolved and estimated by the instrumental method has been compared with the electrochemical weight loss. The dissolution rate in the former is found to be more than in the latter. Suitable explanations have been forwarded for the excess dissolution of magnesium. The change in pH observed during the polarisation at high current densities has also been investigated and explained suitably in this paper.

The voltammetric behaviour of several ß-alkyloxy substituted meso-tetraphenylporphyrins has been investigated. The first oxidation potential of all compounds depends strongly upon the substituent constant G+. In contrast to this the second oxidation potential is insensitive to this constant. Furthermore, rate constants for the first anodic electron transfer process were determined. The estimated data confirm, that the distortion of the porphyrin chromophore induced by the substituents did not affect the electrochemical rate constant significantly.

Inhibition of corrosion of nickel and nickel base (Ni-Mo-Fe) alloy in 4 percent nitric acid has been studied in the presence of some azole compounds, using electrochemical polarization technique, at various concentrations of inhibitors and at different temperatures (25, 35, U5°C). All the inhibitors investigated were able to suppress both the anodic and cathodic processes appreciably for both the systems. However, in each case the inhibition afforded by these molecules towards the corrosion of nickel in nitric acid is always greater than those for nickel base alloy-nitric acid system. Among these inhibitors, 2-mercaptobenzo-thiazole was found to be the most effective inhibitor for both the systems. These inhibitor molecules, though structurally similar do not follow the same mechanism of inhibition. Either of the two mechanisms, viz., adsorption or surface complex formation or sometimes both of these have been found valid for individual inhibitors.

The construction of the EPR microspectroelectroelectrochemical cryostat equipped with non-aqueous reference half-cell with liquid junction is described. The electrochemically generated, chemically unstable, paramagnetic [0=Re(OEt)Cl2(py)2]+ complex cation was in situ detected and characterized by EPR spectroscopy.

Despite the high success rate with the use of stainless steel and titanium materials in orthopaedic and dentistry for hard tissue replacement, repair and augmentation procedures, it became apparent that biodegradation of these implants did occur. In order to investigate the systemic effects of corrosion products released from these metallic implants, in vitro and in vivo studies were undertaken. The results of these studies revels that significant levels of metal species are released into the biological tissues. The properties and advantages of microelectrodes makes them useful tools for quantification and characterisation of released metal species either by performing in vitro or in vivo studies. Microelectrodes are also used to evaluate the surface modification and mineralization processes that occurs at the implants surface. The goal of these studies is to develop a selective microelectrode' which should be able to monitor the species involved in the biodegradation and mineralization processes.

Corrosivity of natural water controls concentration of soluble oxygen and amount of mineral salts. In order to decrease the corrosivity of water are applied deoxygenation and demineralization methods. This article presents investigations on oxygen and mineral salts removal by ion exchangers. A special kind of a bed which contained two ionic forms: sulphite and hydroxyl was investigated for simultaneous removal of oxygen and anions from water. The natural water from a deep well supplied the bed after its initial decationization on strong acid cation exchanger. The model solutions were used with hydrochloric and sulphuric acids in amounts equal to decationization of water from the well, too. It was stated that the removal efficiency of oxygen and anions was very high. The bed may be used as a dysfunctional ionic column for the simultaneous removal of oxygen and anions if demineralization process is designed by ion exchanger's method. The corrosivity of water may be eliminated and technological installation should be simplified using such a bed.

An automatic acquisition and processing system for titration data based on a PC-compatible is described. The main advantages over the commercial available units are the possibility of using a uniform and objective criterion of potential stability, greater flexibility and much lower price. The titration system and its interfacing to the microcomputer is described as well as the controlling software written in GWBASIC. Examples of potentiometric acid-base titrations using the proposed system are discussed.