Scielo RSS http://scielo.pt/rss.php?pid=0872-190420190005&lang=en vol. 37 num. 5 lang. en http://scielo.pt/img/en/fbpelogp.gif http://scielo.pt http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042019000500001&lng=en&nrm=iso&tlng=en A carbon paste electrode has been modified with a red algal species of Porphyridium cruentum, and the characterization of its electro catalytic activity has been done with cyclic voltammetric studies of the potassium ferricyanide (K3(Fe(CN)6)) system. In order to highlight the electrode's stable and fast response to the (Fe(CN)6)3-/(Fe(CN)6)4- redox couple, experiments were also conducted with a bare carbon paste electrode. FTIR spectra revealed the functional moieties of the bare and modified electrodes. The electrochemical surface area and surface coverage capacity were calculated for both electrodes. The effect of the scan rate helped to evaluate the nature of the electrode process, electron transfer mechanism, and kinetic parameters (rate constant and charge transfer coefficient). http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042019000500002&lng=en&nrm=iso&tlng=en Nickel and graphite were potentiostatically co-deposited using a nickel-graphite composite counter electrode (HCE) with tunable-friability. Graphite electrodes were produced at densities of 0.920, 1.026 and 1.188 g/cm³, and their suitability for constitution into HCE was assessed. The surface area of the nickel component was varied from 100% to about 60% and 30 %, and combined with the graphite electrode, to form HCE, designated as triplet, doublet and singlet, respectively. Deposition was done for about 8 hours in 1 M NiSO4, using the different HCE constitutions, an Ag/AgCl reference electrode and a custom deposition head which served as working electrode. The mechanism of graphite electrode unraveling was observed to be the formation of oxygen and CO2, due to oxidation reactions at HCE. The graphite electrode with a density of 0.920 g/cm³ was selected for HCE, due to its extensive surface porosity, a characteristic determined as favorable to the mechanism of electrode unraveling. Co-deposition of graphite with nickel was observed to increase as the nickel surface area was reduced from triplet to singlet. SEM micrographs show partially and fully embedded graphite particles in the nickel matrix, while the presence of nickel and graphite was affirmed. http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042019000500003&lng=en&nrm=iso&tlng=en The corrosion inhibition of zinc coated steel sheets immersed in 3.5% NaCl with sulfisoxazole (SSZ) has been reported by weight loss, potentiodynamic polarization, electrochemical impedance spectroscopy, hydrogen permeation studies and quantum mechanical studies. All these techniques indicate that SSZ significantly inhibits zinc coated steel corrosion in a 3.5% NaCl medium. Polarization studies confirmed that the inhibition mode follows a mixed type. The adsorption of the compounds onto the zinc coated steel surface obeyed Langmuir adsorption isotherm. http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042019000500004&lng=en&nrm=iso&tlng=en The aim of our studies was to show the effect of the addition of tin to aluminum in a solution of sodium chloride (NaCl 3%), by weight, as well as the influence of the alloy immersion time on its corrosion resistance. To do this, we have used, as electrochemical techniques, potentiodynamic polarization and electrochemical impedance spectroscopy and, as metallurgical techniques, hardness parameters and optical microscopy performed on the alloys made of pure aluminum (99.99%) and pure tin (99.99%). The obtained results show that the addition of tin enhances aluminum electrochemical activation, as well as the spontaneous formation of an oxide layer containing Al2O3, which then protects the metal from further corrosion. During all that process, the alloy immersion in 3% NaCl acts by promoting tin's attack and the alloy's corrosion. http://scielo.pt/scielo.php?script=sci_arttext&pid=S0872-19042019000500005&lng=en&nrm=iso&tlng=en The aim of this study was to produce an inexpensive and easy to implement electrochemical sensor. The synthesis of a composite from poly (vinyl alcohol) and natural clay enabled to obtain a material with interesting properties, in view of the results achieved from thermal analysis and transmission electron microscopy. The layer film of natural poly (vinyl alcohol) clays was used to modify the glassy carbon electrode of which electrochemical response was good in the presence of gallic acid in a phosphate buffer solution. The mechanism of electro-oxidation reaction was proposed, and the pH effect has been approached in order to confirm the reaction mechanism. The concentration linearly increased with the oxidation current peak, with a regression coefficient of 0.989 and a detection limit of 1.005 µM (S/N=3). The method thus proposed is satisfactory for the determination of gallic acid in a solution.