Scielo RSS <![CDATA[Portugaliae Electrochimica Acta]]> vol. 26 num. 2 lang. pt <![CDATA[SciELO Logo]]> <![CDATA[<b>Voltammetry of Mercury(II) Based on an Organo-Clay Modified Graphite Electrode</b>]]> Organo-clay complex of ligand-hexadecyltrimethylammonium with montmorillonite was made for the purpose of application as a preconcentration agent in a chemically modified carbon paste electrode for determination of mercury (II) in aqueous solution. It was found out that the adsorption of Hg(II) by organo-clay complex is independent of the pH of the solution. It was also found out that the adsorption of the remaining metals Cd(II), Pb(II), Cu(II), Zn(II), and Ni(II) was dependent on the changes in pH solutions and increased when it varies from 1 to 8. The resultant material was characterized by cyclic and differential pulse anodic voltammetry using a modified graphite paste electrode in different supporting electrolytes. The mercury response was evaluated with respect to pH, electrode composition, preconcentration time, mercury concentration, possible interferences and other variables.<hr/>Argila organo complexada de ligante-hexadeciltrimetilammonium com montmorillonite foi preparada com a finalidade de aplicação como um agente de préconcentração em um eléctrodo de pasta de carbono quimicamente modificado para determinação de mercúrio (II) em solução aquosa. A adsorção de Hg(II) através de complexo da argila organo modificada foi independente do pH da solução. A adsorção dos metais restantes Cd(II), Pb(II), Cu(II), Zn(II), e Ni(II) foi dependente de mudanças do pH das soluções e aumentou quando ele varia de 1 a 8. O material resultante foi caracterizado por voltametria cíclica e de pulso diferencial anódico empregando um eletrodo modificado de pasta de grafite em diferentes eletrólitos de suporte. A resposta do mercúrio foi avaliada relativamente ao pH, composição de eléctrodo, tempo de préconcentração, concentração de mercúrio, possíveis interferentes e outras variáveis. <![CDATA[<b>Cobalt and Molybdate Ions Effects on the Passivation of Iron Based FeCoC Ternary Alloys, in non Deaerated Solution of 10 <sup>-3</sup> M NaHCO<sub>3</sub> + 10<sup>-3</sup> M Na<sub>2</sub>SO<sub>4</sub>, at 25 °C</b>]]> In the present paper, the electrochemical behaviour of four based iron FeCoC ternary alloys was studied in non deaerated solution of 10-3 M NaHCO3 + 10-3 M Na 2SO4, at 25 °C, and compared to that of pure iron and cobalt. The inhibition effect of sodium molybdate has also been considered for different concentrations. It was noted that the oxygen oxidizes the FeCoC ternary alloys except that with the most important cobalt content. For this reason, a potentiodynamic polarisation was carried out at different temperatures (25, 35, 45 and 55°C) in which the current growth versus temperature indicates really that molybdate oxidizes this alloy. <![CDATA[<b>Studies on the Inhibitive Effect of Exudate Gum from <i>Dacroydes edulis</i> on the Acid Corrosion of Aluminium</b>]]> The inhibitive effect of exudate gum from Dacroydes edulis in the corrosion of aluminium in HCl solutions was studied using weight loss and thermometric methods at 30-60 ºC. The results reveal that the exudate gum acts as an inhibitor for corrosion of aluminium in HCl solution. The inhibition efficiency increases with an increase in the concentration of the exudate gum but decreases with increase in temperature. The Temkim adsorption isotherm was tested for its fit to the experimental data. The result confirms that the corrosion inhibition of the exudate gum from DE is attributed to the adsorption of molecules of phytochemicals present in the exudate gum on the surface of the metal. The free energies and equilibrium constant for the adsorption process were determined. A mechanism of physical adsorption is proposed. <![CDATA[<b>Pyrazole Derivatives as Corrosion Inhibitors for Steel in Hydrochloric Acid</b>]]> The effect of 1-{[benzyl-(2-cyano-ethyl)-amino]-methyl}-5-methyl-1H-pyrazole-3-carboxylic acid methyl ester (P1) and 1-{[benzyl-(2-cyano-ethyl)-amino]-methyl}-5-methyl-1H-pyrazole-3-carboxylic acid ethyl ester (P2) was evaluated as corrosion inhibitors of steel in molar hydrochloric using weight loss measurements and electrochemical polarisation. The results obtained reveal that those compounds reduce the corrosion rate. The inhibiting action increases with the concentration of pyrazole compounds to attain 98.5 % at the 10-3 M of (P2). The increase in temperature leads to a decrease in the inhibition efficiency of the compounds in the temperature range 308 - 353 K. The adsorption isotherm of inhibitors on the steel has been determined. The thermodynamic data of activation and adsorption are determined. <![CDATA[<b>Corrosion Inhibition Efficiency of 3-Hydroxy-2-Methylquinazoline-4-one on Mild Steel in 1 M H<sub>2</sub> SO<sub>4 </sub>and 1 M HCl Acid at Different Temperatures</b>]]> The influence of 3-hydroxy-2-methylquinazoline -4-one on the corrosion inhibition of mild steel in 1 M HCl and 1 M H2SO4 has been studied using weight loss, and galvanostatic polarization studies. Result obtained reveals that this organic compound is a very good inhibitor and its inhibition efficiency increases with increasing its concentration to attain 92% at 1000 ppm at 25 ºC. The potentiodynamic polarization study indicates that this compound acts as a mixed type corrosion inhibitor. The rate of corrosion of mild steel rapidly increases with temperature over the temperature range of 25 ºC to 55 ºC, both in absence and presence of the inhibitor. Thermodynamic parameter for adsorption process has been calculated using the Langmuir’s adsorption isotherm. <![CDATA[<b>Effects of Magnesium Sulfate Attack on Ordinary Portland Cement (OPC) Mortars</b>]]> The chemical and mineralogical compositions in Ordinary Portland Cement (OPC) were determined and cement which is low of C3A is more easily exposed to sulfate environment. The relation between physical strength of mortars sized 150 ´ 150 ´ 150 mm and the effects of different concentrations of sulfate solutions, SO4(2-) (1%, 3% and 5%) for 3, 14 and 28 days was found to be that stronger the sulphate concentrations, the greater the sulfate attack, but in a weaker concentration situation, the attack was more efficient as the comparable damaged being achieved with smaller amount of sulphate. The morphological studies were observed under scanning electron microscope (SEM) and the distribution of the main component, including Mg2+ and SO4(2-) ions, was analysed by Energy Dispersive X-Ray Analyzer (EDS) to observe the cracks and reactions.