NATALIA KONDO MONTEIRO
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Artigo IPEN-doc 24469 Low temperature synthesis and properties of gadolinium-doped cerium oxide nanoparticles2017 - MACHADO, M.F.S.; MORAES, L.P.R.; MONTEIRO, N.K.; ESPOSITO, V.; FLORIO, D.Z. de; MARANI, D.; FONSECA, F.C.Gadolinium-doped cerium oxide (GDC) is an attractive ceramic material for solid oxide fuel cells (SOFCs) both as the electrolyte and in composite electrodes operating at low and intermediate temperatures. GDC exhibits high oxygen ion conductivity at a wide range of temperatures and displays a high resistance to carbon deposition when hydrocarbons are used as fuels. However, an inconvenience of ceria-based oxides is the high sintering temperature needed to obtain a fully dense ceramic body. In this study, a green chemistry route for the synthesis of 10 mol% GDC nanoparticles is proposed. The aqueous precipitation method starts from the nitrates of both cerium and gadolinium and uses excess hexamethylenetetramine (HMT) to produce crystalline GDC at 80 ºC. Such a low temperature synthesis provides control over particle size and sinterability of the material at low temperatures.Artigo IPEN-doc 23095 Optimization of spin-coated electrodes for electrolyte-supported solid oxide fuel cells2017 - NOBREGA, SHAYENNE D. da; MONTEIRO, NATALIA K.; TABUTI, FRANCISCO; FLORIO, DANIEL Z. de; FONSECA, FABIO C.Electrodes for electrolyte-supported solid oxide fuel cells (SOFC’s) were fabricated by spin coating. Strontium- doped lanthanum manganite (LSM) cathode and nickel yttria-stabilized zirconia cermet anodes were synthesized and processed for enhanced deposition conditions. The influence of electrode microstructural parameters was investigated by a systematic experimental procedure aiming at optimized electrochemical performance of single cells. Polarization curves showed a strong dependence on both electrode thickness and sintering temperature. By a systematic control of such parameters, the performance of single cells was significantly enhanced due to decreasing of polarization resistance from 26 Ω cm² to 0.6 Ω cm² at 800°C. The results showed that spin-coated electrodes can be optimized for fast and cost effective fabrication of SOFCs.Resumo IPEN-doc 23724 Low temperature synthesis of gadolinium-doped cerium oxide nanoparticles2016 - MORAES, LETICIA P.R. de; MONTEIRO, NATALIA K.; MACHADO, MARINA F. de; ESPOSITO, VINCENZO; FLORIO, DANIEL Z. de; MARANI, DEBORA; FONSECA, FABIO C.In this study, a green chemistry route for the synthesis of gadolinium-doped ceria (GDC) nanoparticles is reported. The aqueous based reflux method uses nitrates of both ceria and gadolinium and hexamethylenetetramine as starting materials to produce GDC at 80 ºC. As-produced powders were found to be crystalline fluoritetype structure GDC before any heat treatment, with crystallite size ≤ 10 nm, as inferred by X-rays diffraction analyses. Energy dispersive X-ray spectroscopy data revealed that GDC powders, with gadolinium concentration in the 0 - 20 mol% range, have composition close to the nominal values, within the experimental error. Thermogravimetric analyses (TG) evidenced that main mass loss (~7%) occurs at < 400 °C. Sintering behavior was studied by dilatometry of cylindrical pellets pressed using both as-produced and calcined (400 °C for 1 hour in air) powders. The retraction profile of the as-produced samples resembles the TG data, showing plateaus that correspond to the observed mass loss events. On the other hand, sintering of calcined samples exhibited onset of shrinkage at T ~ 600 °C and a continuous retraction up to 1400°C (~17% total retraction). The experimental results indicate that the synthesis method results in GDC with good properties for application in electrochemical devices, such as fuel cells and solardriven thermochemical reactors.