AGATHA MATOS MISSO
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Artigo IPEN-doc 23829 Synthesis and characterization of CaMgSi2O6 activated by Eu2+2017 - MISSO, AGATHA M.; BRITO, HEMI F.; RODRIGUES, LUCAS C.V.; MORAIS, VINICIUS R.; YAMAGATA, CHIEKORare earth silicate based MnMgSi2O5+n (M = Ca, Sr or Ba and n=1-2) phosphors, have attracted interest of researchers due to their high efficiency as a host, excellent thermal and chemical stability and high brightness adding to their low cost. These phosphors showed great potential in various applications such as fluorescent lamps, white light emitting diodes, and display components. High temperature solid-state reactions are usually employed to synthesize those compounds. This paper proposes an alternative method of obtaining nanophosphor host based on Eu-doped CaMgSi2O6 (CMS:Eu), persistent luminescence phosphor. Sol gel technique combined to a modified molten salt method was used. The resulted powder was calcined for 3h under an atmosphere of 5% H2 and 95% Ar2. Phase identification by XRD and the measurements of photoluminescence (PL) and photoluminescence excitation (PLE) were performed. Single phased CMS:Eu with persistent luminescence characteristics was prepared.Artigo IPEN-doc 20725 Low temperature synthesis of lanthanum silicate apatite type by modified solgel process2014 - MISSO, AGATHA M.; ELIAS, DANIEL R.; SANTOS, FERNANDO dos; YAMAGATA, CHIEKORare earth silicate apatite type is a very important and promising material for application as an electrolyte in IT-SOFC (Intermediate Temperature Solid Oxide Fuel Cell). Lanthanum silicate apatite, La9.33Si6O26, exhibits high conductivity and has high efficiency, long term stability, fuel flexibility, low emissions and relatively low cost compared to yttria stabilized zirconia (YSZ), at temperatures between 600 and 800 °C. One of the problems of YSZ is its high operating temperature, which results in long starting times and problems of mechanical and chemical compatibility. The interest of investigating lanthanum silicate apatite as an electrolyte is to overcome the problems caused by high temperature operation required by YSZ electrolyte. In the present study, the sol-gel method was used to synthesize La9.33Si6O26. Initially, the reagents (sodium silicate and lanthanum nitrate) were mixed to obtain colloidal silica. Then, this gel containing lanthanum nitrate was thermally treated to allow the melting of lanthanum nitrate salt distributed on colloidal silica. The aim of this study was to verify if this method permits the formation of La9.33Si6O26 pure apatite phase, in order to obtain fine powders and uniform particles for further processing and obtaining a ceramic body.Artigo IPEN-doc 18918 Influence of the precursor concentration on the characteristics of silica powder obtained from Nasub(2)SiOsub(3) by a facile low temperature synthesis process2012 - YAMAGATA, CHIEKO; ELIAS, DANIEL R.; PAIVA, MAYARA R.S.; MISSO, AGATHA M.; MELLO CASTANHO, SONIA R.H.Artigo IPEN-doc 19079 Facile preparation of apatite-type lanthanum silicate by a new water-based sol-gel process2013 - YAMAGATA, CHIEKO; ELIAS, DANIEL R.; PAIVA, MAYARA R.S.; MISSO, AGATHA M.; CASTANHO, SONIA R.H.M.In recent years, apatite-type lanthanum silicates ([Ln10x(XO4)6O3–1.5x] (X = Si or Ge)) have been studied for use in SOFC (solid oxide fuel cells), at low temperature (600–800 8C), due to its ionic conductivity which is higher than that of YSZ (Yttrium Stabilized Zirconia) electrolyte. For this reason they are very promising materials as solid electrolyte for SOFCs. Synthesis of functional nanoparticles is a challenge in the nanotechnology. In this work, apatite-type lanthanum silicate nanoparticles were synthesized by a water-based sol–gel process, i.e., sol–gel technique followed by chemical precipitation of lanthanum hydroxide on the gel of the silica. Na2SiO3 waste solution was used as silica source. Spherical aerogel silica was prepared by acid catalyzed reaction, followed by precipitation of lanthanum hydroxide to obtain the precursor of apatite-type lanthanum silicate. Powders of apatite-type lanthanum silicate achieved from the precursor were characterized by thermal analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM) and specific surface area measurements (BET). The apatite phase was formed at 900 8C.