Navegando por Autor "Gouveia, Deiby Santos"
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Artigo Color and structural analysis of CoxZn7−xSb2O12 pigments(Elsevier, 2006-11-09) Gouveia, Deiby Santos; Soledade, Luiz Edmundo Bastos; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dosThe polymeric precursor method was successfully used to synthesize CoxZn7−xSb2O12 (x = 0–7) powders. Pigments were evaluated using colorimetry, X-ray diffraction, UV–vis and infrared spectroscopy. The optical band gap values vary with the Co2+ substitution. These results suggest that the concomitant presence of Co and Zn in the spinel lattice leads to the rupture of the Végard law, as well as other properties of the studied system, such as unit cell volume. The Co-richer samples display a higher absorbance than the Co-lean samples. The high absorption of the Co7Sb2O12 sample at most of the visible region makes this compound a candidate for a black pigment. It was shown that color depends on the site where the chromophore ion is located, in agreement with the ligand field theory.Artigo Thermal study of CoxZn7-xSb2O12 spinel obtained by pechini method using different alcohols(Springer, 2004-02) Gouveia, Deiby Santos; Rosenhaim, R.; Maurera, M. A. M. A. de; Lima, Severino Jackson Guedes; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dosWith the aim of obtaining materials with applications in pigments, CoxZn7–xSb2O12 spinels were synthesized using the Pechini method. This method consists in the formation of a polymeric net, where the metallic cations are homogeneously distributed. In this work, two types of alcohol (ethyl glycol and ethylene glycol) were used for the synthesis of a zinc antimoniate spinel, CoxZn7–xSb2O12 (x=0–7). The materials were characterized by termogravimetry (TG) and differential thermal analysis (DTA). TG results indicated a decrease in total mass loss when cobalt was added to the solution substituting zinc, for samples prepared using the two different alcohols. Decomposition temperatures, obtained by TG and DTA, presented a decreasing behavior as cobalt was added to the material. In relation to the alcohols, all results indicated a better polymerization of the resin when ethylene glycol was used, being the most indicated one for cation immobilization. X-ray diffraction did not show differences between the two alcohols – both presented the spinel phase (Co, Zn)2.33Sb0.67O4. Samples with higher quantity of cobalt also presented ilmenite phase (Co, Zn)Sb2O6