Portugaliae
Electrochimica Acta

The addition of tefra-alkylammonium salts, namely fefra-methylammonium, tefra-ethylammonium, tefra-butylammonium and tefra-hexylammonium salts, to the supporting electrolyte, in the presence of different metal ions, does not change the observed cathodic current for shorter carbon chains. However, an important effect is observed when n > 4 (number of carbon atoms of each chain). This is shown through the polarograms which were recorded for different solutions of cadmium, zinc and manganese ions, in the presence and absence of those ions. The interpretation based on electrocapillary curves has shown that electron transfer through the double-layer becomes more difficult as the length of the carbon chain increases. Polarographic and electrocapillary experiments were followed all over.

A comment from a reader of a paper on the definition of electrolyte and the author's reply is presented.

The use of in situ infrared (IR) vibrational spectroscopy on the elucidation at a molecular level of electrochemically induced phenomena, i.e., in situ IR spectroelectrochemistry, has been rapidly developing in the last two decades, since a pioneer work of Bewick et al., by using modulation and synchronous detection of the signal in external reflectance IR spectroscopy. In situ IR spectroelectrochemistry has been proved to be a powerful tool for investigation of the electrode solution interface, namely by providing information on the structural, bonding and dynamical properties of adsorbate species on electrode surfaces, on the behaviour of supporting electrolyte and solvent molecules at the electrochemical interface and also on reaction mechanisms and kinetics of electrocatalytic reactions. An overview of some theoretical aspects of IR reflectance spectroscopy is presented and experimental details of some in situ techniques are described, namely EMIRS (Electrochemically Modulated Infrared Reflectance Spectroscopy), SNIFTIRS (Subtractively Normalised Interfacial Fourier Transform Infrared Reflectance Spectroscopy) and SPAIRS (Single Potential Alteration Infrared Reflectance Spectroscopy). A few selected applications of these techniques to electrocatalysis are also presented.

The polarographic and voltammetric reduction of dithizone (1, 5-diphenylthiocarbazon, H2Dz, thiol form I) has been studied in Britton-Robinson buffers (pH 2.10-12.00) containing 50% ethanol at room temperature. The reduction of the compound takes place in single 2e- transfer, giving a diffusion controlled reversible wave in the entire pH range of the study corresponding to the reduction of the azo group. A mechanism is proposed for the reduction process of the compound.

Increased interest in highly conducting polymer electrolytes is clearly evident from the open literature, particularly on the specific area of energy-related applications. Poly(ethylene oxide), PEO, although well studied, continues to intrigue us and must still be regarded as playing a central role in polymer electrolyte research and development. Ion containing organic polymers involving essentially PEO as the solvent matrix are reviewed here. The greatest technological driving force for its continued study is still, by far, the desire for thin film rechargeable batteries that meet a multitude of ambitious energy, power density and safety requirements, while not being prohibitively expensive.

Using square- wave voltammetry at a static mercury drop electrode, a fast and simple method has been developed for the assay of the water-soluble vitaniins tliiamiiie hydrochloride, riboflavin, folic acid and nicotinamide. In Britton Robinson buffer (pll 9.5) by cathodic scan thiamine hydrochloride give a peak at -1.33 V, riboflavin give two peaks at -0.61 V and -0.73 V, folic acid gives a peak at -0.91V and nicotinamide give a peak at -1.74 V vs. Ag/AgCl reference electrode at the same buffer solution. These four vitamins can be determined by the same voltammogram. The reduction peak currents are linearly dependent on the concentration of the vitamins. The method is successfully applied to determine these four vitamins contents of multivitamin preparations simultaneously. The values found agreed well with those determined by other methods.

The electrochemical behaviour of the cyanometalate complexes [Fe(CN)e]4" [W(CN)8]4\ [Os(CN)6]4-, [Mo(CN)8]4" and [Ru(CN)6]4" is investigated at high concentrations of the corresponding potassium salts (0.6 M) in alkaline solution (pH = 13) by voltammetric measurements with a platinum microdisk electrode. Under these experimental conditions the electrode reactions are reversible and the half-wave potentials are about 130 mV more positive than the standard redox potentials of these couples. The analytical characteristics of voltammetric determinations at high concentrations of electroactive species are studied using K4[W(CN)g] as a model compound.

In the present study the voltammetric behaviours of some phenothiazines namely Promazine hydrochloride, Promethazine hydrochloride and Fluphenazine hydrochloride were investigated. And it was shown that the electro oxidation of the substances was dependent on the nature of the supporting electrolyte, pH, scan rate. The results of the statistical analysis revealed that the quantitative analysis of these substances could be made using glassy carbon electrode, activated by a simple electrochemical procedure, with good accuracy and precision.

Mercury film microelectrodes, prepared by potentiostatic electrodeposition of Hg(II) from an acidic solution onto a gold microdisk electrode, in combination with adsorptive stripping voltammetry in the presence of catechol were used to study the behavior of copper, iron and nickel in aqueous solutions. The voltammetric behavior of hydrogen ion was also investigated by performing cyclic voltammetry and stripping voltammetry with mercury microelectrodes.

The use of some p-substituted benzoic acid derivatives as low cost inhibitors for the corrosion of aluminium in 60% H3PO4 solution was explored by weight loss and galvanostatic polarization measurements. The inhibition efficiency of the compounds increases in the order: p-OH > P-NH2 > benzoic acid > p-Br > p-N02- This order is not affected by the variation in temperature in the range 30-60 °C. Rate of corrosion is affected by both concentration of inhibitors and the temperature of the medium. The reaction rate was found to be proportional to the absolute value of Hammett constant (a). Some thermodynamic functions were computed and are discussed. Key words: Corrosion, aluminium, polarization, weight-loss measurements.

Basic concepts of electrochemistry are not yet properly understood in areas related with technical aspects where this science is fundamental, such as corrosion. Examples of this are given here with the objective of alerting electrochemists for the need to give their collaboration in technical bodies (e.g. ISO, CEN, OIML [1]) where it is useful to complement the very important technical knowledge of applied experts on the relevant field (e.g. corrosion) with fundamental knowledge of electrochemistry.

The effect of some 4-amino-4' -nitroazobenzene derivatives as corrosion inhibitors for copper in nitric acid solution at 30 °C was investigated using thermometric and polarization techniques. The corrosion rate was found to be a function of the nature, of inhibitor and temperature of the medium. The calculated degree of concentration surface coverage was used to evaluate the free energy of adsorption (A G°a) of the process. All the inhibitors follow the Frunkin adsorption isotherm. The mechanism of inhibitor action has been discussed on the basis of adsorption and molecular polarizahility of the inhibitors. The observed experimental data indicate that these compounds act as mixed inhibitors. Some thermodynamic function was calculated and discussed. Key words: Corrosion, inhibitors, acid solution, copper, dyes.

A recent survey of secondary school pupils' attitudes to chemical formulae show interesting similarities with the attitudes of XIX century scientists to the formulae system developed by Berzelius (the basis of the present system). Dalton's opposition to this system, Children's alterations of a Berzelius original when translating it to English, a fact praised by contemporaries, and other objections of the time are compared with today's secondary school pupil’s comments collected in a recent study. These comparisons make it easier to understand the difficulties in teaching formulae at school.

The open-ended capillary cell has been used as a reliable method to measure mutual differential diffusion coefficients of a great variety of aqueous solutions of electrolytes [1, 2]. In the last few years we have been developing, with some success, a capillary cell capable of measuring thermodynamic diffusion coefficients of electrolytes imbibed in polymeric matrices [3-5]. We have developed two different systems, called "manual" and "automatic", to measure diffusion coefficients. In this communication we will present an improvement of the "manual" system that permit us to measure a large range of concentrations, from approximately 10 M until at least 2 M, with very good precision, and accuracy.

An electrolyte local composition model is developed to establish an equation to calculate isothermal activity coefficients, in a range of concentrations until 2.5M, for solutions of strong 1-1, 1-2 and 1-3 electrolytes. The validity of the equation with two adjustable parameters has been confirmed on thirty compounds.

Mean activity coefficients of KC1 in water-ethanol solvents were determined, using the Pitzer model, from electromotive force data, at 25 °C. The molalities of KC1 varied from 0.1 mol kg"' to near saturation, in the range 0 to 20 % w/w ethanol. A modified model of the Pitzer equations was also applied to predict the mean activity coefficients of KC1 in water-ethanol and water-methanol mixtures. These results were compared with experimental values.

The electrochemical behaviour, in aprotic medium, of the 18-electron octahedral-type dinitrile complexes ira/«-[Fe(NCR)2(depe)2][BF4]2 (R = alkyl, aryl, NH2, NMe2 or NEt2; depe = Et2PCH2CH2PEt2) was studied by cyclic voltammetry and controlled potential electrolysis. They undergo one single-electron reversible oxidation, and electrochemical ligand and metal site parameters [which measure the electronic properties of the nitrile ligands and their binding iron(II) centre] were estimated from the measured half-wave oxidation potential values.

The electrochemical behaviour of some vanadium complexes with ester ligands, of the types rV2(p-Cl)2CL(L)4] [L=CH3C02Et (1) or 'MMiiCO^ih (2)], and rV4(u-0)4Clg{CH2(C02Et)2}4] (3), was investigated in aprotic media by cyclic voltammetry (CV) and controlled potential electrolysis (CPE) at platinum electrodes. They exhibit, by CV, ill-defined anodic processes which, by CPE, appear to involve one electron per vanadium atom.

The nitride ligand in the complex rra«s-[Mo(N)Cl(dppe)2] reacts with enantiomeric ICH2CONHCH(CH3)COOCH3 to form imide complexes. Sequential nitrogen-carbon and carbon-carbon bond formation, followed by electrochemical Mo-N bond cleavage, defines a pathway to optical active methyl esters of the glycyl-alanine and alanyl-alanine. The key intermediate metallo-nitrogen ylide trans-[MoCl(NCHCONHCH(CH3)COOCH3)(dppe)2] has incipient carbanion character at the a-carbon and reacts with methyl iodide to form C-C bonds.