Lanthanum chromites (LaCrO 3 ) are the main materials used as interconnect for solid oxide fuel cells. However, there are several difficulties involved in the processing of these materials. The objective of this work is to investigate and to characterize the relationships between microstructural development process and the electro-thermal-mechanical behavior of earth-alkaline metals doped lanthanum chromites-based ceramics. Calcium and strontium doped lanthanum chromites-based ceramic powders were produced by solution-based method from respective metallic nitrates. Samples were prepared by pressing and sintering procedures. The phase composition was evaluated by X-ray diffraction and densification level by Archimedes method. The microstructural characterization was made by scanning electron microscopy, energy dispersive X-ray spectroscopy and thermal analysis techniques. Electrical tests were used to evaluate the electrical conductivity of the samples, and thermal expansion coefficient was determined by dilatometric measurements. The obtained experimental results corroborate the literature comments concerning the difficulty of lanthanum chromite-based ceramics with high densification level and evidence the great influence of the nature of the dopants on the sintering mechanism and the microstructural and electric characteristics of the produced ceramics. The best ones results, in terms of densification and homogeneity characteristics, had been gotten through multiple doping with calcium and strontium, and in sintering temperature conditions lower that the normally considered to pure or mono-doped lanthanum chromite-based ceramics.
Controlling surface wettability of ceramic electrical insulators is one of the proposed alternatives to avoid undesired electrical events when these devices are installed in polluted environments. In this sense, the application of super‐hydrophobic nanostructured coatings has recently been proposed due to its high water repellency and possibility of surface self‐cleaning. In this present study, coatings based on polysiloxane, alumina trihydrate (ATH), and several types of silica (SiO2) were developed using a spray‐coating method. Contact angle (CA), sliding angle (SA), thermogravimetric analysis, transmission electron microscopy, scanning electron microscopy (SEM), atomic force microscopy, and inclined plane test (IPT) were applied to characterize fillers and coatings. The results showed that a high quantity of nanoparticles is necessary to achieve superhydrophobicity. The type of silica significantly affected the surface wettability leading to CA from 107 to 160° and SA from 3 to 90°. SEM analysis showed that coatings with hydrophilic silica present a more pronounced topography with microstructured aggregates. The resistance of superhydrophobic coatings to leakage current development was also dependent on type and amount of silica. The superhydrophobic coating with PDMS treated with silica had the best performance during the IPT showing fewer peaks and less accumulated electrical charge.
Pós cerâmicos foram produzidos através da técnica de precipitação a partir de soluções coloidais de compostos metálicos. Sais de zinco foram utilizados sob a forma de cloreto, nitrato e acetato de zinco. Investigou-se a influência do tipo de ânion do sal precursor sobre as características das cerâmicas produzidas. Análise térmica e difração de raios-X foram empregadas na caracterização dos pós obtidos. Microscopia eletrônica de varredura, espectroscopia de raios-X por dispersão de energia, determinação do grau de densificação dos compactos cerâmicos e caracterização elétrica foram utilizadas para avaliar a influência do tipo de ânion do sal precursor sobre as características elétricas e microestruturais das cerâmicas varistoras produzidas. Conclui-se que as cerâmicas produzidas utilizando-se o acetato de zinco como precursor principal apresentaram características de sinterabilidade superiores àquelas das cerâmicas produzidas com o uso de nitrato ou de cloreto de zinco, o que se refletiu em seu melhor desempenho como varistor.
RESUMOEste trabalho tem por objetivo verificar a adequabilidade do uso de concentrados de óxidos de terras-raras (COTR) para a fabricação de varistores à base de óxido de zinco. COTR e misturas produzidas em laboratório foram utilizados na fabricação de varistores à base de óxido de zinco (ZnO) segundo o método cerâmico. Análises granulométricas, térmicas, química por fluorescência de raios-X e de fases por difração de raios-X foram empregadas na caracterização dos COTR. A caracterização microestrutural dos varistores produzidos foi feita a partir dos resultados de microscopia eletrônica de varredura, espectroscopia de raios-X por dispersão de energia e densimetria, e a caracterização elétrica teve por base os dados de tensão-corrente e tensão-capacitância. Os resultados obtidos mostram que existem perspectivas para a utilização de COTR na fabricação de cerâmicas varistoras à base de ZnO, as quais dependem, essencialmente, da natureza das impurezas ou do grau de refino químico dos COTR empregados. Varistores com coeficientes de não-linearidade entre 12 e 40 foram obtidos, alguns com valores de corrente de fuga comparáveis àqueles característicos de varistores comerciais.Palavras chaves: Cerâmicas varistoras, eletrocerâmicas, óxidos de terras-raras.
Characterization and Utilization Prospects of Rare-earth Oxides Concentrated to Zinc Oxide-based Varistor Ceramics Manufacturing
ABSTRACTThis work has for objective to verify the adequateness of the use of rare-earth oxides concentrated to zinc oxide-based varistor ceramics manufacturing. Rare-earth oxides concentrated and mixtures produced in laboratory had been used in the manufacture of zinc oxide-based varistors in accord to conventional ceramic method. Granulometric and thermal analysis, besides X-ray diffraction and fluorescence analysis were used in the characterization of the rare-earth oxides concentrated powders. SEM-EDS analysis and density analysis were used in the microstructural characterization and the electrical characterization was made from voltage-current and voltage-capacitance data. The results obtained show that there are good prospects for the use of rare-earth oxides concentrated in zinc oxide-based varistor ceramics manufacturing, which depend essentially on the nature of the impurities present or on the chemical refine level of the rareearth oxides concentrated used. Varistor ceramics with non-linearity coefficient between 12 and 40 were obtained, some presenting leakage current values comparable to those presented by commercial varistors.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.