Navegando por Autor "Vieira, Fagner Ticiano Gomes"
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Artigo The influence of temperature on the color of TiO2:Cr pigments(Elsevier, 2009-05-06) Vieira, Fagner Ticiano Gomes; Melo, Danniely Silva; Lima, Severino Jackson Guedes de; Silva, Elson Longo da; Paskocimas, Carlos Alberto; Silva Júnior, Wilson; Souza, Antonio Gouveia de; Santos, Iêda Maria Garcia dosTiO2:Cr brown pigments were prepared via a polymeric precursor derived from the Pechini method. The pigments were analyzed by infrared spectroscopy, X-ray diffraction, ultraviolet–vis spectroscopy, and colorimetry. The increase of the calcination temperature from 700 to 1000 8C led to a decrease in the L* values, corresponding to darkening of the pigments. The pigments obtained in this work are darker than those produced by a solid-state reaction method reported before. The change in the pigment color is due to the anatase–rutile phase transition, which leads to a shift in the charge transfer bond (Ti4+$O2 ) due to a change in the crystal field around the chromophore ions. Moreover, the oxidation state of chromium was observed to change, and this also alters the color of the pigmentsArtigo Thermogravimetric and UV–vis spectroscopic studies of chromium redox reactions in rutile pigments(Springer, 2009-06-24) Vieira, Fagner Ticiano Gomes; Souza, Soraia C.; Oliveira, A. L. M.; Lima, Severino Jackson Guedes; Silva, Elson Longo da; Paskocimas, Carlos Alberto; Soledade, Luiz Edmundo Bastos; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dosIn this study undoped and Cr, Sb or Mo doped TiO2 were synthesized by polymeric precursor method and characterized by X-ray diffraction, UV–VIS spectroscopy, infrared spectroscopy and thermogravimetry (TG). The TG curves showed a continuous mass loss assigned to the hydroxyl elimination and Cr6? reduction. Doped TiO2 samples showed a higher mass loss assigned to water and gas elimination at lower temperatures. In these doped materials a decrease in the anatase–rutile phase transition temperature was observed. After calcination at 1,000 C, rutile was obtained as a single phase material without the presence of Cr6?