Artigos
URI permanente para esta coleçãohttps://repositorio.fei.edu.br/handle/FEI/795
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- Surface segregation and consequent so2 sensor response in SnO2-NiO(2005-08-09) HIDALGO, P.; CASTRO, R. H. R.; COELHO, A. V. C.; GOUVEA, D.Many studies have been carried out concerning the development of SO 2 sensors to detect and avoid its health prejudicial effects. However, there is still a lack of reliable, high-speed-response sensors that work at room temperature. In this work, the segregation of Ni in the SnO 2-NiO system is used to obtain a rapid SO2 sensor response. Segregation and its structure consequences were studied by electron dispersive spectroscopy, infrared spectroscopy, and high-resolution transmission electron microscopy in nanopowders of SnO2-NiO with different compositions prepared by a polymeric precursor method. The sensor activity of SnO2-1 mol % Ni was studied and a linear calibration curve was formed with a maximum limit response of 32 ppm SO2. © 2005 American Chemical Society.
- Interface excess and polymorphic stability of nanosized zirconia-magnesia(2008-05-27) Castro R.H.R.; Marcos P.J.B.; Lorriaux A.; Steil M.C.; Gengembre L.; Roussel P.; Gouvea D.Controlling the phase stability of ZrO2 nanoparticles is of major importance in the development of new ZrO2-based nanotechnologies. Because of the fact that in nanoparticles the surface accounts for a larger fraction of the total atoms, the relative phase stability can be controlled throughout the surface composition, which can be tuned by surface excess of one of the components of the system. The objective of this work is to delineate a relationship between surface excess (or solid solution of MgO relative to ZrO2 and the polymorphic stability of (ZrO2) 1-x-(MgO)x nanopowders, where 0.0 ≤ x ≤ 0.6. The nanopowders were prepared by a liquid precursor method at 500 °C and characterized by N2 adsorption (BET), X-ray diffraction (XRD), X-Ray photoelectron spectroscopy (XPS), and Raman spectroscopy. For pure ZrO 2 samples, both tetragonal and monoclinic polymorphs were detected, as expected considering the literature. For MgO molar fractions varying from 0.05 to 0.10, extensive solid solution could not be detected, and a ZrO 2 surface energy reduction, caused by Mg surface excess detected by XPS, promoted tetragonal polymorph thermodynamic stabilization with relation to monoclinic. For MgO molar fractions higher than 0.10 and up to 0.40, Mg solid solution could be detected and induced cubic phase stabilization. MgO periclase was observed only at x = 0.6. A discussion based on the relationship between the surface excess, surface energy, and polymorph stability is presented. © 2008 American Chemical Society.