Portugaliae
Electrochimica Acta

The corrosion behavior of the areas affected by welding of a steel has been performed in aqueous solution, for a synthetic sea water, by the linear polarization resistance method. Using a normalizing heat treatment at 920°C for a duration of 15 min and then air cooling, it shown to be enough to eliminate the structural heterogeneity responsible by the anodic behavior of stress material.

It is reported, for the first time in Portugal, the introduction of the electrochemical noise technique applied to the corrosion monitoring of the cooling circuit of a stator in a thermoelectric power station, allowing in real time, the detection and identification of a localized corrosion process. The circuit uses electrolytic copper in contact with low conductivity water, less than 1 uScm"1. A specially designed probe to be installed in a by-pass fashion to the cooling circuit, was developed by CML, U.K. Results obtained during a monitoring period of 3 months are discussed.

Enquadrada num trabalho mais amplo sobre a redução electroquímica indirecta de corantes, a presente comunicação teve, como objectivo, a selecção de um material de eléctrodo adequado ao complexo de ferro e trietanolamina (Fem/TEA), em meio básico, usado como mediador redox. A análise dos resultados experimentais e dos voltamogramas obtidos permitiu concluir que, dos diferentes materiais testados (aço, ferro e cobre), o cobre parece ser o que permite uma transferência electrónica de maior reversibilidade.

A procedure for quantification of nickel in cell culture medium using a mercury film microelectrode and dimethylglioxime (DMG) as the complexing ligand was developed. The results obtained by adsorptive cathodic stripping voltammetry (AdsCSV) were compared to those attained by atomic absorption spectrometry and good agreement was found.

The analytical conditions for the determination of the total iron in mice organ samples have been optimized and the suitable experimental parameters were found to be a catechol concentration of 3.0x10"4 mol/L, pH ca. 7.2 provided by PIPES buffer concentration of 8.0x103 mol/L, a deposition potential of -1.80 V, deposition time 10-30 s, frequency 50 Hz, step 4 mV and an amplitude of 20 mV. The detection limit was 13.7x10 9 mol/L after a deposition potential of 25 s. The relative standard deviation of fifteen repeated measurements of the same solution was 1.13%, indicating that the peak iron response was very reproducible.

Energy consumption in an electrolytic process is mainly governed by current efficiency and voltage efficiency. Hence an accurate calculation of the current efficiency will greatly help in evaluating energy data precisely. An attempt has been made in this study to perfect an alternate method for calculating the current efficiency (C.E.) from the chlorine gas liberated at the anode during magnesium chloride electrolysis. The anodic current efficiency (A.C.E.) thus obtained has been compared with the cathodic current efficiency (C.C.E.) calculated by metal basis. A difference between the two values has been observed and the reasons for such differences have been analyzed in this paper.

A theoretical model based upon cell configuration (Resistive Network Model) is adopted for calculating the bypass current for a stack of bipolar electrodes used in molten salt electrolysis. A simplified bypass current calculation is also made by using experimentally obtained current and potential in the magnesium cells. The results obtained from both the models are compared and discussed particularly for two different electrolyte compositions.

A definition of electrolyte presented in an international standard is critically discussed.

The electrochemical behaviours of c/s-[ReCI(NCC6H4Me-4)(dppe)2] and of the hydride complex [ReCIH(NCC6H4CI-4)(dppe)2]+ have been studied by cyclic voltammetry (CV) and controlled potential electrolysis (CPE) in aprotic media and at platinum electrodes. The 16-electron dicationic configuration of the former compound undergoes a facile isomerization to its trans isomer in the time scale of CV whereas the hydride complex undergoes an anodically induced deprotonation through an overall bimolecular process. Quantitative analyses of both processes, by digital simulation of cyclic voltammograms, are outlined. The models of Amavadine [VL2]2" [L = "ON(CH(CH3)COO")2 (HIDPA3-) or "ON(CH2COO")2 (HIDA3-)], act as electron-transfer mediators in the electrocatalytic oxidation of thiols. This redox catalysis process is shown to occur through an unprecedented mechanism involving Michaelis-Menten type kinetics.

Diffusion coefficients in aqueous electrolyte solutions have been calculated according to Onsager-Fuoss and Pikal theories for over 301 electrolytes in aqueous solutions using the most reliable data.

From the polarographic studies of (E-i)t and (i-t)E curves the reduction of chromate ion in the DME has been analysed in order to verify both the irreversibility and the kinetic parameters of the processes. The study has been followed in aqueous and mixed H20-EtOH (15, 30% weight EtOH) media, with 0.1M NaOH at 25°C. A modified version of the OLDHAM-PARRY method is proposed and the possibilities of "sampled current-voltammetry" through instantaneous current, are also emphasized.

Voltammetric studies were carried out using a glassy carbon working electrode to determine the concentration of oxide ion in a CsCI-KCI-NaCI eutectic melt. The mechanism of electrode process and some kinetic parameters were established. The oxidation of O2 is irreversible two-stage process complicated by adsorption. The diffusion coefficient of oxide ions changes from 5.62-106 to 1.99-TO6cm2 s1 at 750-59CPC. The equation for the calculation of oxide ion concentration was derived.

The values of the hydration equilibrium constants of carbonyl and a-dicarbonyl compounds given in the literature are reviewed; the experimental methods used to the calculation of these constants are discussed as well. The values of the correspond mg constants of glyoxal, methylglyoxal and phenylglyoxal are discussed, the last by using a Taft-type correlation.

The redox properties of some tetrakis(pyrazolyl)borate rhenium(V) complexes of the types [ReO{ri3-B(pz)4}L](L= "0^0" type ligand, 1/2L= MeO") and [ReO{r|2-B(pz)4}(OMe)L'] (L'= 0°0" , >To", type ligands) were studied by cyclicvoltammetry. These Re(V) complexes display generally one anodic and one cathodic waves, at values of potential which are discussed in terms of the hapticity of the pyrazolylborate ligand and of the electronic properties of the chelating co-ligands.

The redox properties of complexes of general formulae [{FeCl3L}2], [{CuCl2L}2] and [PdCl2L2] (L=camphor-type ligand) were studied by cyclic voltammetry and controlled potential electrolysis. As a general behaviour, the complexes display at least one cathodic wave which has a marked metal character. The potentials are discussed on the basis of the electronic properties of the camphor-type ligands. Extensive reductive controlled potential electrolysis of one of the diiron complexes allowed the electrosynthesis of a mononuclear product. The electrochemical behaviour of the L ligands [L=A (R=Ph or Pr1) and L=B (R=NH2)] is also reported.

By cyclic voltammetry (CV) in aqueous solutions of KC1, the Amavadine models [NBu4]2[VL2] (L = HIDPA3' - N-hydroxy-a,a'-iminodipropionate - or HIDAV - N-hydroxy-a,a'-iminodiacetate) undergo a single-electron reversible oxidation. The anodically generated Vv species acts as an electron-transfer mediator in the electrocatalytic oxidation of some thiols and evidence is presented for the involvement of an interaction between the substrate (mercaptopropionic acid) and the vanadium complex. The mechanism has been investigated by CV simulation and a preliminary account is now being discussed.