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.

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.

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.

The degradation of a reactive blue 4 dye in acidic solution has been compared using electrochemical reduction and oxidation at reticulated vitreous carbon electrode (RVC) and Ti/SnO2/SbOx (3%mol)/RuO2 (30%mol) electrodes and photo-Fenton method under UV irradiation. The reduction of RB4 dye at -0.6 V on RVC electrode results in 50% of color removal and up to 64% of TOC removal. The direct oxidation of RB4 dye at +1 V on RVC promotes only the oxidation of amine group and there is no color removal. On SnO2 electrode, 58% TOC was removed and the decolorization is around 100 % after 1 hour of electrolysis at 2.4 V indicating good efficiency. Best performance was obtained by photo-Fenton method that indicates 80% elimination of TOC and 100% of color removal but the method requires oxidant addition and time of rest to remove the generated residues.