A new methodology using gas-diffusion microextraction (GDME) was developed for the analysis of volatile corrosion inhibitors (VCIs). The evaluation of the inhibition efficiency and corrosion rate (ν) was performed by NaCl deliquescence tests and correlated with measurements of polarization resistance (Rp) obtained from electrochemical impedance spectroscopy (EIS) analysis and with the pH resulting from the atmosphere of the inhibitor (pHGDME). The correlation obtained between n and pHGDME indicates that the higher the value of pHGDME the lower the corrosion rate. The Raman spectra of steel was used to monitor in situ adsorption of VCI and the surface modifications caused by the inhibitors. The scanning electron microscopy (SEM) images corroborate the data of ν, both indicating that the cyclohexylamine vapor showed the best corrosion resistance performance.

The construction of gold electrodes using 3 kinds of gold recordable compact discs (CDtrodes) and characterization by electrochemical and spectroscopic techniques are herein reported. Following a surface pretreatment in 0.5 mol L-1 sulfuric acid (H2SO4), the electrochemical experiments were performed in the presence of redox couple ferro/ferricyanide [Fe(CN)6]3-/4-. The immobilization of an oligopeptide bio-inspired by acetylcholinesterase onto the CDtrode was also evaluated. Surface characterization was done by cyclic voltammetry, electrochemical impedance spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy and atomic force microscopy. CDtrodes are known to be of low cost, fast and simple construction. They are suitable for immobilizing biological molecules and could be used as disposable transducer for the construction of biosensors.

This study evaluates the interaction of volatile corrosion inhibitors (VCIs) of the amino group with the zinc or zinc oxide surface by means of computational calculations using density functional theory (DFT) and comparing with experimental methods such as electrochemical impedance spectroscopy (EIS) and wet chamber tests. The application of these methods allowed indicating the most promising VCI and understanding its mechanism of action. Thus, after the vaporization of VCI molecules, they condense on the surface and form a protective film or a film with oxidizing characteristic, thereby preventing the corrosive action of the chemical species present in the environment.

A influência do etanol, ácido sulfúrico e cloreto na resistência à corrosão do aço 316L foi investigada por meio de curvas de polarização e medidas de espectroscopia de impedância eletroquímica. No intervalo estudado, o potencial de corrosão do aço foi independente das concentrações de H2SO4 e NaCl em solução aquosa. Por outro lado, em solução contendo 65% (m/m) de etanol e 35% (m/m) de água, os potencias de corrosão foram mais altos do que os observados em solução aquosa. Além disso, o potencial de corrosão do aço foi alterado pela adição de H2SO4 e NaCl em solução. Em soluções com e sem etanol, mais 0,35% (m/m) de NaCl, a presença de 1% (m/m) de H2SO4 inibiu o aparecimento de corrosão puntiforme.

The influence of ethanol, sulfuric acid and chloride on the corrosion resistance of 316L stainless steel was investigated by means of polarization curves and electrochemical impedance spectroscopy measurements. Over the studied range, the steel corrosion potential was independent of H2SO4 and NaCl concentrations in aqueous solution. On the other hand, in solution containing 65 wt.% ethanol and 35 wt.% water, the corrosion potentials were higher than those obtained in aqueous solution. Besides, the steel corrosion potential was affected by the addition of H2SO4 and NaCl in solution. In solutions with and without ethanol, plus 0.35 wt.% NaCl, the presence of 1 wt.% H2SO4 inhibited the appearance of pitting corrosion.

Silver containing heavy metal oxide glasses and glass ceramics of the system WO3-SbPO4-PbO-AgCl with different AgCl contents have been prepared and their thermal, structural and optical properties characterized. Glass ceramics containing metallic silver nanoparticles have been prepared by annealing glass samples at temperatures above the glass transition and analyzed by transmission electron microscopy and energy dispersive X-ray microanalysis. The presence of the metallic clusters has been also confirmed by the observation of a surface plasmon resonance band in the visible range. Cyclic voltammetric measurements indicated the presence of metallic silver into the glasses, even before to perform the thermal treatment.

The use of carbon paste electrodes (CPE) of mineral sulfides can be useful for electrochemical studies to overcome problems by using massive ones. Using CPE-chalcopyrite some variables were electrochemically evaluated. These variables were: (i) the atmosphere of preparation (air or argon) of CPE and elapsed time till its use; (ii) scan rate for voltammetric measurements and (iii) chalcopyrite concentration in the CPE. Based on cyclic voltammetry, open-circuit potential and electrochemical impedance results the recommendations are: oxygen-free atmosphere to prepare and kept the CPE until around two ours, scan rates from 10 to 40 mV s-1, and chalcopyrite concentrations > 20%.

A influência da concentração de Al nas transformações de fase em ligas de Cu-Al-Ag foi estudada por análise térmica diferencial clássica (ATD), microscopia óptica (MO) e difratometria de raios X (DRX). Os resultados indicaram que o aumento no teor de Al e a presença de Ag diminuem a velocidade da reação de decomposição da fase <FONT FACE=Symbol>b</font>1 e contribuem para o aumento da temperatura desta transição, diminuindo assim o intervalo de estabilidade da fase perlítica, resultante da reação de decomposição.

The influence of the Al content on the phase transformations in Cu-Al-Ag alloys was studied by classical differential thermal analysis (DTA), optical microscopy (OM) and X-ray diffractometry (XRD). The results indicated that the increase in the Al content and the presence of Ag decrease the rate of the <FONT FACE=Symbol>b</font>1 phase decomposition reaction and contribute for the raise of this transition temperature, thus decreasing the stability range of the perlitic phase resulted from the b1 decomposition reaction.

CoFe films were electrodeposited on platinum and copper from an acidic sulfate bath. The deposits surface morphology was analyzed using SEM and composition was determined by XPS. For deposition potentials lower than -0.80 V (SCE), the anodic stripping voltammogram showed a complex anodic current peak evidencing the complexity of the deposition process. Analysis of the deposition current transient curves showed that the nature of the substrate influenced the kinetic of the process: it was observed an instantaneous nucleation on Pt and a progressive nucleation on Cu. Pure cobalt and cobalt-iron films formed on Pt and on Cu presented binding energies for Co2p3/2 signal corresponding to cobalt oxide, while the Fe2p3/2 signal is related to metallic iron. The corresponding metallic cobalt was observed for the Co2p3/2 signal with binding energy of about 778.0 eV.

Cyclic voltammetry and surface analysis techniques (EDX microanalysis, mapping of elements and SEM images) have been used to study the solid state reactions of Ir in blank solution or Hg(I)-containing solution. The studies in KNO3/HNO3 solution permit to suggest the formation of a thin oxide layer film deposited in the substrate. The RCV process exhibits the decrease of capacitive current associated to the substrate surface restructuring. The electro deposition of Hg occurs initially in UPD condition from Hg(I)-containing solution, C Hg(I) = 3.51x10-7 mol L-1. The electro deposition of bulk mercury occurs from Hg(I)-containing solution, C Hg(I) = 3.51x10-5 mol L-1. It was observed the deposition of Hg in the substrate in open circuit for all employed conditions.

Cyclic voltammetry and controlled potential electrolysis, and other analytical techniques were used to study the reactions of mercury with iridium oxides formed by repetitive cyclic voltammetry (RCV) or by controlled potential electrolysis (CPE) on pure iridium substrate. The oxides were formed in a Hg(I)-containing solution. The SEM images, XPS spectra and CV obtained after the RCV treatment showed a more attacked surface with less mercury on the Ir. On the contrary, the SEM images, XPS spectra and the CV for the electrode prepared by CPE indicated a less attacked surface with more Hg. The oxides formed when the CPE condition was applied inhibited the UPD of mercury.