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.

Estudos eletroquímicos localizados de grãos individuais de uma liga policristalina Cu-16%Zn-8%Al foram realizados em solução de tampão borato (pH 8,4) por meio da técnica eletroquímica com microcapilar. As orientações dos grãos, determinadas pelo método de retro-reflexão de Laue, foram predominantemente próximas à direção [110], sugerindo uma texturização da amostra. As medidas de potencial em circuito aberto mostraram que o menor potencial de estado estacionário foi observado para o grão que possui o maior número de degraus na superfície da liga. Os experimentos de voltametria cíclica sugeriram que a orientação do Cu2O segue a orientação do substrato na liga Cu-Zn-Al, enquanto que CuO cresce independentemente.

Local electrochemical studies of single grains of a polycrystalline Cu-16%Zn-8%Al alloy were investigated in borate buffer solution (pH 8.4) by means of microelectrochemical technique. The grain orientations, which were determined by the Laue back-reflection method, were predominantly close to [110] direction, suggesting that the sample was texturized. The open circuit potential measurements showed that the lower steady state potential was observed for the grain which has the highest number of steps on the alloy surface. The cyclic voltammetry experiments suggested that the orientation of Cu2O follows the substrate one in the Cu-Zn-Al alloy, while CuO grows independently.

O comportamento eletroquímico da liga Cu-9%Al-5%Ni-2%Mn em diferentes concentrações de NaCl e valores de pH foi estudado por potencial em circuito aberto (E CA), voltametria cíclica e curvas de polarização. As curvas E CA mostraram uma considerável influência da concentração de NaCl e do pH da solução nos valores de potencial de estado estacionário. Foi observado pelos perfis I/E que a variação da velocidade de varredura indicou a formação de um filme poroso de baixa condutividade o qual foi o responsável pelo aumento linear de corrente, devido à resistência da solução contida nos poros do filme. Com o intuito de investigar os produtos formados durante a varredura de potencial, o potencial foi mantido em diferentes valores de potencial aplicado dos voltamogramas cíclicos e analisado por MO, MEV e EDX. Em geral, foi observada a presença de precipitados de CuCl em potenciais aplicados iguais a 0,20; 0,85 e 0,00 V (vs. Ag/AgCl/KCl(3 mol L-1)) e somente Cu em -0,70; -1,00 e -1,35 V. Nestes últimos, uma camada de Cu foi observada na superfície da liga devido à redução de cloreto cuproso. Este filme bloqueou o aparecimento dos picos de EDX relacionados aos outros metais presentes na liga. As curvas de polarização para a liga Cu-9%Al-5%Ni-2%Mn mostraram que E CA variou conforme o pH da solução e a concentração de NaCl. Conforme a concentração de NaCl aumentou, E CA tornou-se mais negativo para os três valores de pH estudados. Os coeficientes de Tafel foram calculados das curvas de polarização e os valores foram de 60 e 120 mV década-1, para a região anódica e catódica, respectivamente.

The electrochemical behavior of Cu-9%Al-5%Ni-2%Mn alloy in different NaCl concentrantions and pHs was studied by means of open-circuit potential (E OC), cyclic voltammetry and polarization curves. The E OC curves showed a considerable influence of NaCl concentration and solution pH in the steady-state potential values. It was observed by the I/E profiles that the scan rate variation indicated the formation of a porous film of low conductivity which was the responsible by the linear increase of current due to the solution resistance contained in the film pores. In order to investigate the products formed during the potential scan, the potential was held at different values of applied potential of the cyclic voltammogram and analyzed by OM, SEM and EDS. In general, it was noticed the presence of CuCl precipitates in applied potentials equals to 0.20, 0.85 and 0.00 V (vs. Ag/AgCl/KCl(3 mol L-1)) and only Cu in -0.70, -1.00 and -1.35 V. In the latter cases, a Cu layer was observed on the alloy surface due to the cuprous chloride reduction. This film blocked the EDS peaks appearance related to the other metals present in the alloy. The polarization curves for Cu-9%Al-5%Ni-2%Mn showed that E OC varied according to the solution pH and NaCl concentration. As the NaCl concentrantion increased the E OC became more negative for the three pHs studied. The Tafel coefficients were calculated from the polarization curves and the values were 60 and 120 mV decade-1, for anodic and cathodic region, respectively.

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%.

Eletrodos de bornita foram caracterizados na presença e na ausência de Acidithiobacillus ferrooxidans, um importante microorganismo envolvido nos processos de lixiviação de metais. A presença da bactéria modificou significativamente a interface mineral/eletrólito, aumentando a taxa de corrosão, como revelado pelas análises interferométricas, AEM, ICP e EIS. A atividade bacteriana sobre o eletrodo de bornita o tornou poroso e conseqüentemente aumentaram sua área e heterogeneidade. Este comportamento foi correlacionado com a evolução dos diagramas de impedância obtidos durante o tempo do experimento. A principal diferença nestes diagramas foi a presença de uma característica indutiva (até 44 h), a qual está relacionada com a ação bacteriana sobre a dissolução do mineral e não com sua adesão. A impedância real total medida na presença da bactéria foi cerca de 10 vezes menor do que na sua ausência, devido a aceleração na dissolução do mineral, uma vez que é mantido o meio oxidante.

Bornite electrodes were characterized in the absence or in the presence of Acidithiobacillus ferrooxidans, which is an important microorganism involved in metal bioleaching processes. The presence of the bacterium modified the mineral/electrolyte interface, increasing the corrosion rate, as revealed by interferometric, AEM, ICP and EIS analyses. As a consequence of bacterial activity the electrode became porous, increasing its surface heterogeneity. This behavior was correlated with the evolution of impedance diagrams obtained during the time course of experiments. The main difference in these diagrams was the presence of an inductive feature (up to 44 h), which was related to bacterial action on the mineral dissolution, better than to its adhesion on the bornite. The total real impedance measured in presence of the bacterium was about 10 times lower than in its absence, due to the acceleration of the mineral dissolution, because an oxidant environment was maintained.

Neste trabalho procurou-se descrever detalhadamente o procedimento de preparo de um arranjo de eletrodos com geometria em forma de microdiscos (20,2 < r e < 25,7 mim) e estudar o comportamento eletroquímico desse conjunto de microeletrodos. Foram aplicadas diferentes equações descritas na literatura para a condição de estado estacionário e quase-estacionário e equações para a simulação de voltamogramas em regime estacionário. Para baixas velocidades, v <= 0,1 mV s-1, observou-se uma excelente sobreposição dos voltamogramas cíclicos experimental e simulado, entretanto, velocidades desta ordem de grandeza são pouco práticas do ponto de vista experimental. Observou-se, também para todos os microeletrodos estudados, uma transição da condição de corrente estacionária para quase-estacionária, com o aumento dos valores de v. Equações que permitem avaliar a contribuição das correntes radial e difusional, para a corrente total, ajustam-se perfeitamente as curvas I/E em todo o intervalo de raios dos eletrodos e valores de v empregados. Os voltamogramas obtidos para o arranjo de eletrodos operando na condição de curto circuito apresentou um fator de amplificação de 19 vezes, referente ao sinal obtido a partir de um único microeletrodo. Tal fator confirma a condição de ausência de sobreposição das camadas de difusão dos eletrodos e, portanto, reflete a contribuição individual de cada eletrodo para a corrente total.

In this work we are able to describe in detail the procedure to prepare an array of microelectrodes with flat disc geometry (20,2 < r e < 25,7 mum) and to study the electrochemistry behaviour of the set of microelectrodes. Different equations described in the literature for the steady state and near steady state condition and equations for voltammograms simulation in stationary regime were applied. For v= 0,1 mVs-1, it was observed an excellent overlap between experimental and simulated I / E profiles, however, v of this magnitude are no practice from na experimental point of view. For all of microelectrodes studied, it was observed a transition from the steady state to a near-steady state condition, when the scan rate was increased. The mathematical equations used to evaluate the ciclic voltammograms considering the contribution of the linear and radial diffusion to the total current fitted very well the I / E profiles. These equations also allowed a simultaneous evaluation of all electrodes of the array regarding microelectrodes individual behaviour. These results agree with voltammograms obtained for the array operating in externally short circuited condition.

Estudou-se e discutiu-se os diferentes métodos de preparação de microfios de Pt pura, Pt-Ir (20%, m/m) e Pt-Rh (10%, m/m) a serem empregados na construção dos respectivos microeletrodos. Os fios de Pt e suas ligas foram obtidos empregando fieiras com diferentes diâmetros. Em seguida foi utilizado o procedimento de desgaste eletroquímico em sal fundido (mistura NaNO3/ NaCl 14: a 320oC) para a Pt e em solução 6 molL-1 NaCN + 2 mol L-1 NaOH para a liga de Pt-Ir. Para a caracterização da interface metal-vidro e determinação dos raios geométrico e efetivo foram empregadas as microscopias óptica e eletrônica de varredura, a voltametria cíclica e a cronoamperometria. A condição de selagem foi verificada através dos gráficos da capacitância aparente Cd, corrigida considerando-se a área dos microeletrodos, e a velocidade de varredura, v.

Platinum, platinum-iridium (20 wt.%) and platinum-rhodium (10 wt.%) alloys were prepared as microwires using different methods. Microwires of Pt and its alloys with several diameters were prepared by passing wires of 1 mm of diameter through a drawplate. Afterwards, the Pt microwire was weared electrochemically in a fused salt mixture (NaNO3/NaCl: 4:1; 320°C) applying a square potential wave (1-50 Hz; 2.5 V). Microwires of Pt-Ir and Pt-Rh alloys were prepared applying a sine-shaped AC potential wave (60 Hz, 3-8 V rms), in 6 M NaCN + 2 M NaOH aqueous solution. The characterization of the interface metal-insulating material and the determination of geometric and effective radii of microelectrodes were carried out by means of optical and scanning electron microscopy, cyclic voltammetry and cronoamperometry. The Cd - v plot, where Cd is the apparent capacitance corrected by the electrode area and v the scan potential sweep was used to verify the interface metal-glass sealing conditions.