Zinc electrodes were polarized cathodically at moderate overpotentials in NaCl 0.6 M solutions under potentiostatic conditions for 7 to 17 hours at room temperature. Corrosion products were characterized by using optical microscopy, XRD, Raman microscopy, XPS, and FIB-SEM. Close to the open-circuit potential, the corrosion products were formed by simonkolleite and the electrochemical response exhibits anodic features. At more negative potentials, the current density remains cathodic throughout the polarization and the deposits on the electrode surface consist almost solely of ZnO. The soluble zinc species necessary for ZnO deposition originate from localized dissolution of the substrate in the form of pits. This effect is assigned to the strong alkalinization of the surface due to oxygen reduction. Despite developing greater surface area than bare zinc substrates, the nanostructured ZnO deposits reduced the cathodic activity.[a] Dr.

Corrosion performance of Zr-based coating on substrates obtained by zinc electrodeposition in an alkaline bath is compared to chromate coatings (Cr III and Cr VI). The "nano Zr" is a conversion coating formed by immersion in a hexafluorozirconic acid solution. Since the "nano Zr" coating is transparent, the addiction of a colorant provides color to the surface. In this case, the colorant, when applied after the conversion coating, conferred the yellow color to the surface. The coating produced improves the corrosion protection of the substrate. For this study the samples were analyzed by electrochemical impedance spectroscopy (EIS) and accelerated corrosion test in a humidity chamber. The results showed similar behaviors between the "nano Zr", colorant and the chromate (Cr III) coating. Therefore this kind of conversion coating is a promising substitute for chromate coatings. Keywords: Nano Zr; Immersion process; Electrodeposited zinc; Hexafluorozirconic alkaline solution. COMPORTAMENTO DA CORROSÃO DE UM REVESTIMENTO DE CONVERSÃO À BASE DE ZIRCÔNIO E CORANTES NO AÇO ZINCADO POR ELETRODEPOSIÇÃO ResumoNo presente estudo, avaliou-se o desempenho de revestimentos à base de zircônio e corante sobre substratos de zinco obtidos por eletrodeposição em meio alcalino, em relação aos revestimentos de cromato (CrIII e CrVI). O revestimento "nano Zr" é obtido através da imersão em solução de conversão à base de ácido hexafluorzircônio. Uma vez que o revestimento "nano Zr" é transparente, a adição de um corante proporciona cor à superfície. Neste caso, o corante, quando aplicado depois do revestimento de conversão, confere cor amarela à superfície. O revestimento produzido melhora a proteção contra a corrosão do substrato. Para este estudo ensaios de espectroscopia de impedância eletroquímica (EIS) e testes em câmara úmida foram feitos. Os resultados mostraram comportamentos semelhantes entre o "Zr nano" e corante e o revestimento cromato (CrIII). Por conseguinte, este tipo de revestimento de conversão é um promissor substituto para os revestimentos de cromatização. Palavras-chave: Nano Zr; Processo de imersão; Zinco eletrodepositado; Solução ácida de hexaflúorzircônio.

Zinc oxide (ZnO) films with nano-granular structure were deposited by radio-frequency magnetron sputtering. The absence of preferred orientation was verified by XRD. HAADF-STEM images revealed a nanoporous structure with pore and grain sizes around 10 nm. The narrowness of the pores enabled to approximate that oxygen reduction takes place at the surface of the layers. During cathodic polarization, the surface of the electrodes became rougher due to the development of nodules on the surface. The ZnO electrodes exhibit a high activity towards oxygen reduction in KOH solution (pH = 10). Rotating ring-disk electrode measurements coupled with reaction modelling allowed to quantitatively demonstrate that the direct reduction prevailed with the indirect pathway being active as well.[a] Dr.

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The degradation of sputtered columnar ZnO layers under DC polarization was studied by using electrochemical impedance spectroscopy and electron microscopy. It was found that the structure of the as-deposited ZnO film was dense at the nanoscale. An equivalent circuit model including de Levie impedance accounted for the localized propagation of microscale cracks towards the copper substrate. This generates a capacitance (C ZnO ) that represents the crack surface area in contact with the electrolyte. C ZnO is small enough not to be obscured by the double layer capacitance at the top of the layers and increases with increasingly negative potential and time. These results were compared to nanoporous ZnO layers that behave differently and exhibit a large C ZnO . The combination of in situ EIS analysis with the ex situ structural information provided by electron microscopy proved to be an efficient methodology to characterize very different microstructures of conductive coatings.

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