The evolution of TiO 2 nanotubular morphology, synthesized in a mixture of fluorinated ethylene glycol and glycerol electrolyte, was studied as a function of the anodization time. The samples were characterized by FEG-SEM, XRD, XPS, UV-Vis and EIS. The formation of single-or double-walled TiO 2 nanotube structure can be efficiently controlled by the anodization time. For anodization times less than 30 minutes, a compact oxide layer is formed, followed by double-walled nanotube formation up to 120 minutes and single-walled nanotubes up to 240 minutes. XPS analyses show that the samples obtained with short anodization time have a high carbon content and oxygenated surface species compared to the longer-time anodized sample; however, binding energy peaks for Ti 2p remained invariant. The performances of TiO 2 nanotubular photoelectrodes were evaluated in photoelectrochemical water splitting where TiO 2 nanotubes anodized for 120 minutes presented the best performance that was related to their optimal morphology and charge transportation.
Anodizing of ferritic stainless steel has been used for decoration purposes to obtain a barrier effect. The most commonly used electrolyte for this process is INCO (5M H<sub>2</sub>SO<sub>4</sub> + 2,5M CrO<sub>3</sub>). INCO electrolyte with glycerin addition induces the formation of ordered porous structures, because glycerin reduces the electrolyte conductivity. Ferritic stainless steel was anodized in electrolyte composed by 2M H<sub>2</sub>SO<sub>4</sub> with glycerin addition in different concentrations, without chromium oxide addition. It was observed that the addition of 90 v/v% glycerin promoted a reduction in the electrolyte conductivity, which caused an increase in the anodizing potential. The glycerin addition to the electrolyte diminished the oxide dissolution in the electrolytic solution, promoting the formation of an oxide with an ordered porous structure.
Ferritic stainless steels exhibit properties, such as good electrical conductivity, good corrosion resistance and low cost, that are beneficial for their application as interconnects in intermediate temperature solid oxide fuel cells (ITSOFC) that function at temperatures between 600°C and 800°C. However, the stainless steel corrosion resistance is attributed to the amount of Cr, which is an element that forms a chromium oxide (Cr2O3) layer, acts as an oxidation protective barrier at high temperatures, and reduces the interconnector performance due to its low electrical conductivity. In this context, the objective of this work was to obtain spinel coatings from the Fe and Ni metallic alloy thermal conversion on AISI stainless steel 430 substrate produced by electrodeposition. The morphology and microstructure of the spinel films deposited on stainless steel were characterized by SEM, EDS, XRD and adherence analysis. The results obtained showed that the films were adherent, dense and continuous along the AISI stainless steel 430 substrate surface. In addition, the heat treatment procedure effectively produced crystalline spinels ((NiFe)3O4).
Studies have been performed to improve the oxidation resistance of ferritic stainless steels at high temperatures because these materials have been proposed for the manufacture of interconnectors for solid oxide fuel cell (SOFCs) and solid oxide electrolysis cells (SOECs) operating at intermediate temperatures (IT-SOFCs). Among the coatings employed, ceramic spinel-type oxides have been the most frequently applied. In this context, Mn-Co-based coatings were deposited on ferritic stainless steel (AISI 430) in this study using a dip-coating technique. The obtained coatings were characterized with respect to their morphology by SEM, their elementary composition by EDS and their structure by XRD. It was possible to produce continuous and adherent Mn-Co-based coatings on the surface of the metallic substrates.
Estudos vêm sendo desenvolvidos para melhorar a resistência à oxidação em temperaturas elevadas do aço inoxidável ferrítico, os quais têm sido propostos para fabricação de interconectores de células a combustível do tipo óxido sólido de temperatura intermediária (IT-SOFC). Dentre os revestimentos empregados, os revestimentos cerâmicos de óxidos do tipo espinélio têm sido os mais aplicados. Nesse contexto, no presente trabalho foram obtidos revestimentos à base de Mn e Co sobre aço inoxidável ferrítico (AISI 430), utilizando a técnica de dip-coating. Os filmes obtidos foram caracterizados quanto à morfologia por MEV e quanto à composição elementar por EDS. Foi possível obter do revestimento à base de Mn e Co continuo e aderente sobre o substrato metálico.
The rapid growth in the production of biodiesel and it's primary co-product, i.e. glycerol, has become an environment concern. Currently, several processes have been developed to convert glycerol to other compounds through catalysis. Herein, nanotubular morphology of titanium dioxide (TiO 2) was obtained by electrochemical anodization and applied in photocatalytic degradation of glycerol. Nanostructured TiO 2 catalysts were obtained by anodization in glycerol-ethylene glycol electrolyte containing ammonium fluoride at 60 V for time durations of 60 and 120 minutes and crystallized through thermal treatment at 450 °C for 3 h with a heating ramp of 10 ºC min-1. The samples were characterized by FEG-SEM and XRD. The performances of TiO 2 nanotubular photoelectrodes were evaluated via glycerol photodegradation and also for comparison in photo-electrochemical water splitting. The TiO 2 nanotubes anodized for 120 minutes presented the best performance in both tests that was related to their optimal morphology and charge transportation.
Os aços inoxidáveis ferríticos apresentam características como, boa condutividade elétrica, boa resistência à corrosão e baixo custo, e uma das aplicações tem sido como interconectores em células a combustível de óxido sólido de temperatura intermediaria (ITSOFC), que operam a uma temperatura entre 600ºC a 800ºC. No entanto, a boa resistência à corrosão desta liga é atribuída à quantidade de Cr que em elevadas temperaturas forma uma película protetora de óxido de cromo (Cr2O3), prejudicando o desempenho dos interconectores. Nesse contexto, o presente trabalho tem por objetivo obter filmes de espinélios a base de Fe e Ni através da técnica de eletrodeposição. Os filmes de espinélios obtidos sobre o aço inoxidável foram caracterizados quanto à morfologia e microestrutura por MEV, EDS, DRX, e quanto à aderência. Os resultados obtidos mostraram que o filme é aderente ao substrato de aço inox AISI 430 e após tratamento térmico foi possível obter espinélios (NiFe)3O4.
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