Portugaliae
Electrochimica Acta

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.