Navegando por Autor "Souza, Iedo A."
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Artigo Structural and spectroscopic characterization of Al2−x Cr x O3 powders obtained by polymeric precursor method(Springer, 2007-03-21) Cava, Sérgio; Benincá, Renata; Tebcherani, Sérgio Mazurek; Souza, Iedo A.; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Varela, José A.Al2O3 and Al2−xCrxO3 (x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy (reflectance spectra and CIEL∗a∗b∗ color data). The obtained results allow to identify the γ -Al2O3 to α-Al2O3 phase transition. The single-phase α-Al2O3 powder was obtained after heat treatment at 1050 ◦C for 2 h. The results show that the green to red color transition and ruby luminescence lines observed for the powders of Al2−xCrxO3 are related to the γ to α-Al2O3 phase transition and the temperature and time range for such transition depends on the chromium contentArtigo Structural characterization of phase transition of Al2O3 nanopowders obtained by polymeric precursor method(Elsevier, 2007-06-15) Cava, Sérgio; Tebcherani, Sérgio Mazurek; Souza, Iedo A.; Pianaro, Sidnei Antônio; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Varela, José A.Nanocrystalline Al2O3powders have been synthesized by the polymeric precursor method. A study of the evolution of crystalline phases of obtained powders was accomplished through X-ray diffraction, micro-Raman spectroscopy and refinement of the structures through the Rietveld method. The results obtained allow the identification of three steps on the -Al2O3 to -Al2O3 phase transition. The single-phase -Al2O3 powder was obtained after heat-treatment at 1050 ◦ C for 2 h. A study of the morphology of the particles was accomplished through measures of crystallite size, specific surface area and transmission electronic microscopy. The particle size is closely related to -Al2O3 to -Al2O3 phase transition