Navegando por Autor "Rajesh, Surendran"

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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 precursors
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 do
This 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
One-step synthesis and microstructure of CuO-SDC composites
(FapUNIFESP (SciELO), 2017-03) Nascimento, Rubens Maribondo do; Firmino, Hellen Cristina Torrano; Araújo, A. J. M.; Dutra, Ricardo P. S.; Rajesh, Surendran; Macedo, Daniel Araújo de
An in situ one step synthesis route based on the polymeric precursor method was used to produce dual phase CuO-samaria doped ceria (SDC) nanocomposite powders. This chemical route allowed to obtain composite powders with reduced particle size and uniform distribution of Cu, Ce and Sm elements. The particulate material was characterized by powder X-ray diffraction (XRD) combined with Rietveld refinement. CuO-SDC sintered in air between 950 to 1050 °C and subsequently reduced to Cu-SDC cermets were further characterized by XRD and scanning electron microscopy. The open porosity was measured using the Archimedes’ principle. Suitable microstructures for both charge transfer and mass transport processes (30 to 45% porosity) were attained in Cu-SDC cermets previously fired at 1000 to 1050 °C. Overall results indicated that CuO-SDC composites and Cu-SDC cermets with potential application as anodes for solid oxide fuel cells (SOFCs) can be obtained by microstructural design. An anode supported half-cell was prepared by co-pressing and co-firing gadolinia doped ceria (CGO) and the herein synthesized CuO-SDC nanocomposite powder
One-step synthesis of composite electrolytes of Eu-doped ceria and alkali metal carbonates
(Elsevier, 2013-12-13) Nascimento, Rubens Maribondo do; Rajesh, Surendran; Macedo, Daniel Araújo de; Souza, Graziele Lopes de; Figueiredo, Filipe Miguel Henriques Lebre Ramos; Marques, Fernando M. B.
Europium-doped ceria (EDC, Ce0.9Eu0.1O2 d)/alkaline carbonate (LNC, (Li,Na)2CO3) composite ceramics prepared through a one-step citrate-based route were analyzed by powder X-ray diffraction, infrared and laser Raman spectroscopies as well as scanning and transmission electron microscopy. The electrochemical behavior of the electrolyte material was studied by impedance spectroscopy in air, CO2 and N2 þ H2 (90/10 vol%, respectively) gas mixtures, in the temperature range 300e600 C. The sub micrometric and even nanosized ceramic particles appeared as merged inside the mixed carbonates, with modest grain to grain necking. The EDC/LNC composite electrolytes showed a conductivity of 0.27 S cm 1 at 600 C in air, amongst the best ever reported, exceeding the usual requirements for fuel cell applications
Synthesis and properties of CuO-doped Ce0.9Gd0.1O2 δ electrolytes for SOFCs
(Elsevier, 2015-04) Lima, Chrystian G.M.; Santos, Thamyscira H.; Grilo, João Paulo de Freitas; Dutra, Ricardo P.S.; Nascimento, Rubens Maribondo do; Rajesh, Surendran; Fonseca, Fábio C.; Macedo, Daniel Araújo de
The effects of copper oxide (CuO) addition on the crystal structure, densification and microstructure of Gd-doped ceria (Ce0.9Gd0.1O2 δ, CGO) synthesized by the polymeric precursor method have been studied. Ce0.9 xGd0.1CuxO2 δ (0rxr0.01) precursor powders were calcined at 600 1C for 1 h and the phase formation was studied by powder X-ray diffraction combined with Rietveld refinement analysis. Relative density measurements and microstructural analysis were performed on pellets sintered in the temperature range 1000–1100 1C in air. The effect of CuO as a sintering aid becomes more visible when its content is in the 0.5–1 mol% range where the relative densities are found to be 98% for sintering temperature as low as 1000 1C. A remarkable reduction (up to 500 1C) in the sintering temperature for 1 mol% CuO-doped CGO ceramics is observed together with the formation of a dissolved phase of Gd2O3–CeO2–CuO. Ce0.89Gd0.1Cu0.01 yO2 δ sintered at 1000 1C shows total electrical conductivity of 15.5 mS cm 1 at 600 1C slightly higher than Ce0.9Gd0.1O2 δ sintered at 1500 1C (12.4 mS cm 1).

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Navegando por Autor "Rajesh, Surendran"