Portugaliae
Electrochimica Acta

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.

A technique to obtain normalized current was conceived for the cases in which the electrode surface corrodes. Each polarization curve point is obtained with an untreated electrode, which is submitted to two potential jumps: the first jump was applied to measure the current-potential relation. The second one was used for area normalization. Stainless steels 316 and 316 L have been used in a concentrated chloride solution.

The basic redox properties of sulpiride are investigated by means of cyclic (CV) and square-wave voltammetry at a hanging mercury drop electrode (HMDE). Sulpiride undergoes electrochemical reduction in a basic medium. The voltammetric response strongly depends on pH of the medium. A square-wave voltammetric method for quantitative determination of sulpiride is developed. A detection limit of 1.9E-6 mol/I sulpiride was obtained at the static mercury drop electrode in 2 mol/l KOH. The correlation coefficients of the calibration curves at concentration levels of 1E-5 and 1E-6 mol/I are greater than 0.99. The results of recovery tests for added sulpiride from 5.7 to 11.1E-5 mol/l ranged from 91.3 to 106 %, with relative standard deviations from 0.3 to 2.1 %.

The electrochemical behavior of copper in 4.0M HNO3 solutions without and with different concentrations from two organic compounds were studied using both galvanostatic polarization and cyclic voltammetric techniques. These two organic compounds (namely: bis [4-amino-5-hydroxy-l,2,4-triazol-3-yl] methane "compound Dj" and bis [4-amino-5-hydroxy-l,2,4-triazol-3-yl] butane "compound D2") acted as mixed inhibitor type with predominate cathodic effectiveness. Their high inhibition efficiency (>99%) may be due to adsorption of the additive itself and its further interference with the two partial processes. The results obtained from galvanostatic polarization technique are in consistent with that obtained from cyclic voltammetric measurements.

The oxidative adsorption of 0.1 M methanol in 1 M HC104 on Pt(lll), (110), (100) and Pt(poly) electrodes was studied by cyclic voltammetry. Freshly prepared single crystals were immersed in methanol-containing solution at 0.05 V vs. rhe. The voltammetric profiles of the very first positive-going potential scan exhibit a well defined anodic current peak around 0.40 V only for the Pt(100) face. The peak current (ip) and potential (Ep) were evaluated as function of the potential sweep rate. The adsorption process was assigned to an irreversible surface reaction of methanol with Pt (100) leading to the formation of oxidative adsorbed intermediates. The interpretation of the experimental data indicates that the second electron transfer, i.e. the second deprotonation reaction of CH3OH, was the rate-determining step.

Al-Li alloy 8090 and a binary alloy with the same lithium contents (2.5 wt-%) were studied in regard to their corrosion susceptibility in chloride containing solutions using electrochemical methods. Data were compared with results obtained for pure aluminium in the same experimental conditions The effect of lithium ions on aluminium passivation has been demonstrated previously as particularly effective in alkaline solutions, with the obtained film having a protective character and an inhibitive action on the pitting nucleation process. In this work voltammetric and impedance spectroscopy studies were carried out in presence and absence of lithium ions, in alkaline solutions. Chloride ions were added in concentrations varying from 0.001M to 0.6M allowing pitting potentials to be determined and confirming the role the lithium ions in the promotion of corrosion resistance of aluminium and aluminium alloys.

Transition metal compounds like oxides , sulphides, nitrides, carbides , silicides etc are finding extensive importance in the electrical and electronic devices. LiNiC>2 has greater potential demand in advanced battery research. LiNiCh has been identified as one of the most effective cathode materials in rocking chair battery. Though these compounds could be synthesized by solid state reaction like precursor, sol- gel , co-precipitation etc, they can be conveniently deposited in a fine crystalline form by molten salt electrolysis , employing suitable melts and electrodes . LiNi02 was deposited on Ni anode from a melt of LiOH -NaOH at 1023 - 1123 K . The cell set-up, mainly the Ni cell with the Ni electrodes, melt composition and pretreatment, the favourable operating temperature and current density for the deposition of this transition metal oxides in fine crystalline form etc, have been presented in this paper. The properties of these oxides mainly the chemical composition, XRD data etc, have also been studied and reported.

This paper describes the evaluation of a flow injection system with voltammetric multi-site detection, which enables the detector to carry out the measure of the sample at different positions in the manifold. Some advantages of these systems are partially discussed. A voltammetric cell with a tubular configuration and small inner volume (105 p.1) is proposed. This configuration has a very reduced effect on the hydrodynamic characteristics of the flow which makes it most attractive for manifolds with sequential detection. The manifold optimization was carried out using potassium hexacyanoferrate (II) in order to achieve a good separation of both analytical signals, a minimal sample dispersion and a high sampling rate.

An electroanalytical method for the quantification of bentazon in the presence of MCPA has been developed. Both bentazon and MCPA are herbicides used in rice cultures and bentazon appears alone or mixed with MCPA in a proportion of 7:1 in commercial formulations. In this work the interference caused by MCPA was evaluated and it was shown that the use of Triton in the supporting electrolyte solution leads to the elimination of its interference with bentazon.

Computer simulation methods are now well established and powerful tools for studying very many problems of chemical interest. Phase transitions, electrical and thermal conductivity, surfaces and adsorption, liquid crystals, structure and dynamics of polymers, electrochemical interfaces, metal oxides, chemical reactivity, catalysis and drug design are examples of problems that can be approached by computer simulation. In this paper we shall focus on computer simulation in Statistical Thermodynamics, namely the Molecular Dynamics and Monte Carlo methods. The present achievements, future challenges and some applications with interest for Electrochemistry will be reviewed.

The influence of the synthesis potential on the kinetics of electropolymerization and the properties of a hybrid material polypyrrole doped with heteropolytungstate was studied in organic solutions by potential steps and cyclic voltammetry techniques. It was found the presence of side reactions at low potentials when thin films were electrogenerated. The productivity of the hybrid material kept always a high constant value whatever the studied potentials.

The influences of the polymerisation condition on both, production and properties of electrochemically synthesised polypyrrole film in presence of poly(maleic acid-co-olefin) were studied. Polymerisation variables as polymerisation potentials, polarisation times, concentration of pyrrole and concentration of poly(maleic acid-co-olefin) were followed by their influence on both, productivity of the polymerisation charge and the ability to store charge in every electrogenerated film.

The aim of this work is to check that the poly 2,5-di-(2-thienyl)pyrrole, poly(SNS), is a linear polymer which behaves, from an electrochemical point of view as an organic metal. Like inorganic metals poly(SNS) oxidizes, reduces, dissolves and deposits electrochemically. The polymeric films can be electrodissolved by flow of a cathodic current and are able to be electrodeposited again by flow of an anodic current through a solution containing soluble reduced polymer.

A study of many physical and electrochemical properties such as refractive index and specific conductance of the ternary system water-dimethylsulfoxide-copper sulphate as a function of temperature (in the interval 20 °C-50 °C) is reported, as well as the variations for the peak potentials in the cyclic voltammograms, at several temperatures (between 20 °C and 80 °C) of copper sulphate 1 mM in many water-dimethylsulfoxide mixtures and the galvanic potentials at 20 °C of some metallic electrodes in water-dimethylsulfoxide mixtures.

BaSn0.9Sb0.1O3 /Ti electrodes were prepared by painting a slurry containing the oxide, synthesised by high-temperature solid state reaction, and Triton X-100 on titanium supports. The electrochemical behaviour of the electrodes was studied by cyclic voltammetry. From the voltammetric data the electrodes surface roughness was estimated and it was possible to conclude that an insulating film of TiC>2 is formed at the support/oxide layer interface.

In this study, conducting polymer films were synthesised by electrochemical polymerisation of aniline on the stainless steel substrates, and such films were employed for the process of electroless precipitation of silver. The electropolymerisation mode and conditions were carefully selected to provide films displaying structure and electroactivity appropriate to the process. The influence on the metal recovery efficiency of the both PANI surface area and electrolyte composition was also analysed.