Navegando por Autor "Figueiredo, Filipe M. L."
Agora exibindo 1 - 2 de 2
- Resultados por página
- Opções de Ordenação
Artigo Effect of composition on the structural development and electrical conductivity of NiO-GDC composites obtained by one-step synthesis(Elsevier, 2017-08) Nascimento, Rubens Maribondo do; Grilo, João Paulo de Freitas; Moura, Caroline Gomes; Macedo, Daniel Araújo de; Rajesh, Surendran; Figueiredo, Filipe M. L.; Marques, Fernando M. B.NiO-C0.9Gd0.1O1.95 (NiO-GDC) composites obtained using a chemical route (one-step synthesis) were characterized by thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and impedance spectroscopy (between 300 and 650 °C in air). Rietveld refinement of XRD data indicated that synthesized powders are ultrafine and the crystallite size of the GDC phase decreases with increasing NiO content. The relative density of sintered samples is influenced by the NiO content, but easily brought to values above 95% after sintering at 1450–1500 °C. NiO-GDC composites exhibited homogeneous phase distribution and grain size often lower than 1 μm. With 30–40 wt% NiO this phase dominates the overall electrical conductivity of NiO-GDC. The combination of grain size, conductivity and microstructural characteristics shows the efficacy of the adopted processing route to obtain high quality Ni-GDC cermet precursorsArtigo Electrical properties of lanthanum silicate apatite electrolytes prepared by an innovative chemical route(Electrochemical Society, 2014-09-29) Martinelli, Antonio Eduardo; Macedo, Graziele Lopes; Macedo, Daniel Araújo de; Rajesh, Surendran; Figueiredo, Filipe M. L.; Marques, Fernando M. B.; Nascimento, Rubens Maribondo doThis work reports the synthesis of apatite-type lanthanum silicate powders with nominal composition La10Si6O27 by an innovative chemical route which combines co-precipitation and sol-gel approaches. The herein proposed synthetic procedure is advantageous in reducing energy consumption and processing time, key elements to decrease the total manufacturing cost. The asprepared powder was calcined between 500 and 900 °C. Structure of the calcined powders, characterized by X-ray diffraction (XRD) and Rietveld refinement, indicated the formation of apatite crystalline lanthanum silicate with minor amount of L2O3 at 900 °C. The apatite powder was further analyzed by scanning electron microscopy (SEM). The effect of sintering temperature, ranging from 1400 to 1450 °C, on the electrical properties was investigated by impedance spectroscopy. Electrical measurements were recorded in the 400 – 800 °C temperature range. The lanthanum silicate electrolyte sintered at 1450 °C exhibited total electrical conductivity (σ700 ºC = 2.12 x 10-3 S.cm-1) comparable with samples from literature prepared by sol-gel and freeze drying methods and sintered at 1500 °C. The results in the present study demonstrate that the co-precipitation method combined with a solgel approach is a promising alternative route to synthesize lanthanum silicate powders