Engenharia de Materiais
URI permanente desta comunidadehttps://repositorio.fei.edu.br/handle/FEI/17
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3 resultados
Resultados da Pesquisa
- Quantification of MgO surface excess on the SnO 2 nanoparticles and relationship with nanostability and growth(2011-02-15) GOUVEA, D.; PEREIRA, G. J.; GENGEMBRE, L.; STEIL, M. C.; ROUSSEL, P.; RUBBENS, A.; HIDALGO, P.; CASTRO, R. H. R.In this work, we experimentally showed that the spontaneous segregation of MgO as surface excess in MgO doped SnO 2 nanoparticles plays an important role in the system's energetics and stability. Using X-ray fluorescence in specially treated samples, we quantitatively determined the fraction of MgO forming surface excess when doping SnO 2 with several different concentrations and established a relationship between this amount and the surface energy of the nanoparticles using the Gibbs approach. We concluded that the amount of Mg ions on the surface was directly related to the nanoparticles total free energy, in a sense that the dopant will always spontaneously distribute itself to minimize it if enough diffusion is provided. Because we were dealing with nanosized particles, the effect of MgO on the surface was particularly important and has a direct effect on the equilibrium particle size (nanoparticle stability), such that the lower the surface energy is, the smaller the particle sizes are, evidencing and quantifying the thermodynamic basis of using additives to control SnO 2 nanoparticles stability. © 2010 Elsevier B.V.
- Erratum: Quantification of MgO surface excess on the SnO 2 nanoparticles and relationship with nanostability and growth (Applied Surface Science (2011) 257 (4219-4226))(2014) Gouvea D.; Pereira G.J.; Gengembre L.; Steil M.C.; Roussel P.; Rubbens A.; Hidalgo P.; Castro R.H.R.
- Surface modification of SnO 2 nanoparticles containing Mg or Fe: Effects on sintering(2007) Castro R.H.R.; Pereira G.J.; Gouvea D.Controlling the surface chemistry of oxide systems has emerged an effective tool to obtain desirable nanostructures and macro properties. A relatively simple way to achieve this is by using dopants that are prone to segregate to the surfaces of the powders. In this work, we delineate the effect of Mg and Fe on SnO 2 nanopowders focusing on the surface modifications caused by surface segregation. The effects of increasing the temperature of calcinations are particularly addressed to evaluate the surface modifications at high temperatures. The powders were studied by infrared spectroscopy, zeta potential measurements, X-ray diffraction, and specific surface area measurements. Since sintering is a high-temperature process strongly dependent on surface characteristics, we drawn a relationship between the final densities after sintering and the surface chemistry of the doped powders. Doped SnO 2 pellets were sintered to over 95% of the theoretical density within a few seconds (fast firing) when significant surface modifications were observed. © 2006 Elsevier B.V. All rights reserved.