Navegando por Autor "Souza, Antônio Gouveia de"

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Black and green pigments based on chromium–cobalt spinels
(Elsevier, 2011-09-15) Eliziário, Sayonara A.; Andrade, Jeferson M. de; Lima, Severino Jackson Guedes; Paskocimas, Carlos Alberto; Soledade, Luiz Edmundo Bastos; Hammer, Peter; Silva, Elson Longo da; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dos
Chromium and cobalt oxides are widely used in the manufacture of industrial pigments. In this work, the Co(Co2−xCrx)O4 powders with different chromium concentrations (x = 0, 0.25 and 1) were synthesized by the polymeric precursor method, heat treatment between 600 and 1000 °C. These powders were characterized by X-ray diffraction, infrared spectroscopy, colorimetry, UV–vis absorption and X-ray photoelectron spectroscopies. Even with the addition of chromium, the XRD patterns revealed that all powders crystallize in a single spinel cubic structure. The spinels with higher cobalt amount, Co(CoCr)O4 and Co(Co1.75Cr0.25)O4, displayed a dark color, without the Co3+ reduction observed in Co3O4 between 900 and 950 °C. The spinel with higher chromium amount, CoCr2O4, was green. The colors were directly related to the occupation of tetrahedral and octahedral sites by the chromophores, as well as to the different oxidation states of chromium and cobalt. The different optical band gap values estimated from UV–vis spectra suggested the existence of intermediary energy levels within the band gap. X-ray photoelectron spectroscopy confirmed an increasing presence of Co(III) and a decreasing amount of Cr(VI) with cobalt enrichment
Ceramic crucibles: a new alternative for melting of PbO–BiO1.5–GaO1.5 glasses
(Elsevier, 2002-07-10) Santos, Ieda Maria Garcia dos; Moreira, Rafael Carlos Martins; Souza, Antônio Gouveia de; Lebullenger, Ronan; Hernandes, Antônio Carlos; Leite, Edson Roberto; Paskocimas, Carlos Alberto; Silva, Elson Longo da
PbO–Bi2O3–Ga2O3 glasses present interesting properties such as good transmission in the mid-infrared region, high magnetic Verdet constant and non-linear properties. The processing of these heavy-metal-oxide (HMO) glasses is limited by the high corrosive nature of the melt, even in relation to noble metal crucibles. In this work, three kinds of ceramic crucibles (alumina, tin oxide and zirconia) were tested for melting HMO glasses. The main physical properties of the prepared glasses, such as the characteristic temperatures, optical transmission were studied in function of the crucible nature, time/temperature melting parameters. The incorporation of crucible material in the glasses was determined by ICP and atomic absorption. Themaximumglass contamination fromthe crucible was 2.9, 1.6 and 3.6mol% forAl2O3, SnO2 and ZrO2 crucibles, respectively, whenmelting was done at 900 C/240min, for zirconia crucibles and at 1000 C/60 min, for the other two crucibles. The evolution of the physical properties was discussed as a function of contamination degree
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 dos
The 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.
Efeito da adição de rejeito na redução de coração negro em cerâmicas vermelhas
(ABCERAM, 2005) Santos, Ieda Maria Garcia dos; Silva, J. M.; Trindade, M. F. S.; Soledade, Luiz Edmundo Bastos; Souza, Antônio Gouveia de; Paskocimas, Carlos Alberto; Silva, Elson Longo da
Um dos problemas que afeta a indústria cerâmica é a elevada perda de produtos acabados, decorrente do próprio processamento, levando a trincas e peças fora de conformidade. Deste modo, é necessário o reaproveitamento desses resíduos, como forma de reduzir o impacto ambiental. Neste trabalho, os resíduos de duas indústrias de cerâmica vermelha foram moídos e adicionados à própria massa, levando, também, a um ganho econômico. As porcentagens variaram de 10% a 30%, em peso. As peças foram conformadas por extrusão e sinterizadas a 950 ºC e 1000 ºC. Os resultados obtidos mostram que a adição levou a uma melhoria nas propriedades das amostras, pois diminuem a possibilidade de ocorrência de coração negro, levando a peças mais uniformes e menos porosas.
Effect of the modifier ion on the properties of MgFe2O4 and ZnFe2O4 pigments
(Springer, 2007-03-07) Xavier, Camila S.; Candeia, R. A.; Bernardi, M. I. B; Lima, S. J. G.; Silva, Elson Longo da; Paskocimas, Carlos Alberto; Soledade, Luiz Edmundo Bastos; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dos
Magnesium and zinc ferrites have been prepared by the polymeric precursor method. The organic material decomposition was studied by thermogravimetry (TG) and differential thermal analysis (DTA). The variation of crystalline phases and particle morphology with calcination temperature were investigated using X-ray diffraction (XRD) and scanning electronic microscopy (SEM), respectively. The colors of the ferrites were evaluated using colorimetry. Magnesium ferrite crystallizes above 800°C, presenting a yellow-orange color with a reflectance peak at the 600–650 nm range, while zinc ferrite crystallizes at 600°C, with a reflectance peak between 650–700 nm, corresponding to the red-brick color
Influence of doping on the preferential growth of α-MoO3
(Elsevier, 2008-07-14) Pereira, Luiza G.; Soledade, Luiz Edmundo Bastos; Ferreira, Jailson M.; Lima, Severino Jackson Guedes; Fernandes Júnior, Valter José; Araújo, Antônio Souza de; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Santos, Maria Rita de Cássia; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dos
MoO3 is a lamellar material with applications in different areas, as solid lubricants, catalysis, solar cells, etc. In the present work, MoO3 powders, synthesized by the polymeric precursor method, were doped with nickel or cobalt. The powder precursors were characterized by TG/DTA. After calcination between 500 and 700 ◦C, the samples were characterized by X-ray diffraction, infrared and Raman spectroscopy and scanning electron microscopy. -MoO3 was obtained after calcination at low temperatures. With the temperature increase, -MoO3 is observed, with a preferential growth of the (0 2k 0) planes, when the material is doped and calcined at 700 ◦C. Doping with nickel increases five times the preferential growth. As a consequence, plate-like particles are observed
Influence of the network former on the properties of magnesium spinels
(Springer, 2007-03-07) Silva, Márcia R. S.; Miranda, Lydianne C. de O.; Santos, Maria Rita de Cássia; Lima, Severino Jackson Guedes; Soledade, Luiz Edmundo Bastos; Silva, Elson Longo da; Paskocimas, Carlos Alberto; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dos
Undoped and/or doped with 1 mol% of Co2+ Mg2TiO4 andMg2SnO4 powders were synthesized by the polymeric precursor method. The influence of the network former (Sn4+ or Ti4+) on the thermal, structural and optical properties was investigated. The recorded mass losses are due to the escape of water and adsorbed gases and to the elimination of the organic matter. Mg2TiO4 crystallizes at lower temperatures and also presents more ordered structure with a smaller unit call and having more intense green color than Mg2SnO4 has
O papel dos modificadores de rede na produção da fotoluminescência no CaWO4
(ABCERAM, 2004-01) Ciaco, F. R. C.; Pontes, F. M.; Pinheiro, C. D.; Leite, Edson Roberto; Lázaro, S. R. de; Varela, José A.; Pizani, Paulo Sérgio; Paskocimas, Carlos Alberto; Souza, Antônio Gouveia de; Silva, Elson Longo da
Discutiu-se a fotoluminescência para o tungstato de cálcio amorfo, observada à temperatura ambiente. Verificou-se que há concordância entre os resultados experimentais e teóricos. Neste trabalho foram simuladas as estruturas cristalinas e amorfas do tungstato de cálcio (CaWO4), comparando-se as respectivas estruturas eletrônicas. Os resultados dos cálculos teóricos indicam a formação de novos níveis de energia na banda de valência e de condução do amorfo. Estes níveis eletrônicos extras são os responsáveis pela formação da cauda na curva do espectro de absorção. Correspondentemente, medidas experimentais de absorção óptica mostraram a presença da cauda, com relação ao espectro do cristalino. Desta forma, pode-se interpretar a formação da cauda, como sendo associada aos defeitos promovidos na estrutura desordenada do material amorfo
Photoluminescence in the CaxSr1 xWO4 system at room temperature
(Elsevier, 2008-08) Pôrto, S. L.; Silva, Elson Longo da; Pizani, Paulo Sérgio; Boschi, Tania M.; Simões, Luis Gustavo Pagotto; Lima, Severino Jackson Guedes; Ferreira, Jailson M.; Soledade, Luiz Edmundo Bastos; Espinoza, J. W. M.; Santos, Maria Rita de Cássia; Maurera, Maria Aldeiza M. A.; Paskocimas, Carlos Alberto; Santos, Ieda Maria Garcia dos; Souza, Antônio Gouveia de
In this work, a study was undertaken about the structural and photoluminescent properties, at room temperature, of powder samples from the CaxSr1 xWO4 (x ¼ 0–1.0) system, synthesized by a soft chemical method and heat treated between 400 and 700 1C. The material was characterized using Infrared, UV–vis and Raman spectroscopy and XRD. The most intense PL emission was obtained for the sample calcined at 600 1C, which is neither highly disordered (400–500 1C), nor completely ordered (700 1C). Corroborating the role of disorder in the PL phenomenon, the most intense PL response was not observed for pure CaWO4 or SrWO4, but for Ca0.6Sr0.4WO4. The PL emission spectra could be separated into two Gaussian curves. The lower wavelength peak is placed around 530 nm, and the higher wavelength peak at about 690 nm. Similar results were reported in the literature for both CaWO4 and SrWO4
Planejamento experimental aplicado à otimização de massas cerâmicas contendo matérias-primas naturais
(ABCERAM, 2007) Albuquerque, F. R.; Santos, Ieda Maria Garcia dos; Lima, Severino Jackson Guedes; Santos, Maria Rita de Cássia; Soledade, Luiz Edmundo Bastos; Souza, Antônio Gouveia de; Martinelli, Antonio Eduardo
A otimização da composição é uma etapa de fundamental importância no processamento cerâmico. Neste trabalho, planejamento experimental foi aplicado a fim de se avaliar a relação entre propriedade e a composição de um sistema obtido a partir de matérias-primas naturais extraídas no Pegmatito do Seridó, na região fronteiriça RN-PB. Para o estudo do sistema ternário foram combinadas variáveis de processo (temperatura: 1100 e 1200 oC; patamar de calcinação: 0 e 2 h), com a utilização de planejamento de misturas, de acordo com o planejamento simplex centróide. Os percentuais mínimos de cada componente na mistura foram de 10% v/v. Foram avaliadas as propriedades reológicas de suspensões aquosas das misturas com 50% v/v, otimizadas com PAA-Na. Determinou-se a porosidade aparente e massa específica aparente, além da retração de queima. A composição mineralógica das peças cerâmicas obtidas a 1200oC foi basicamente mulita e quartzo. O estudo permitiu especificar a região de composição que leva à maior densidade após sinterização, com um número relativamente pequeno de amostras
Preparação de tunsgstatos cerâmicos do tipo scheelita com propriedades luminescentes
(Universidade Federal do Rio Grande do Norte, 2002) Maurera, Maria Aldeiza Meireles Almeida; Souza, Antônio Gouveia de; Silva, Elson Longo da; http://lattes.cnpq.br/9848311210578810; Melo, Dulce Maria de Araújo; http://lattes.cnpq.br/3318871716111536; http://lattes.cnpq.br/7481128465396350; http://lattes.cnpq.br/9447499731344673; Fernandes Junior, Valter José; http://lattes.cnpq.br/1595902438130772
O desenvolvimento de materiais com propriedades ópticas é de grande importância tecnológica. Na forma cristalina, tungstatos de fórmula AWO4 (A= Ca, Sr, Ba e Pb) é um isolante com um largo gap de energia e de interesse comercial devido a sua atrativa propriedade luminescente. Nesse trabalho foi identificada a fotoluminescência desses materiais no estado desordenado. Os compostos foram sintetizados a baixa temperatura como filmes finos e pós. Para deposição dos filmes foi usado “spin-coating” sobre diferentes substratos. As condições de deposição foram otimizadas em substrato de vidro. Os filmes foram tratados a temperaturas entre 200 e 600 °C e os pós entre 300 e 700 °C. Utilizouse as técnicas de difração de raios X, microscopia de força atómica, espectroscopia de absorção na região do infravermelho e raman para caracterização das fases. Foi verificada a formação de material monofásico de estrutura tetragonal tipo scheelita. A caracterização óptica dos filmes por meio de espectroscopia na região UV-Visível, mostrou que os filmes cristalinos apresentam um gap de energia maior que os filmes amorfos. Isto se deve, provavelmente ao aparecimento de defeitos na estrutura desordenada que provoca absorções ópticas em energias inferiores à do gap do material cristalino. Estudos da fototuminescência em função do tempo e da temperatura de calcinação, bem como da moagem, mostraram que essa emissão está presente quando o sistema encontra-se em estado desordenado e não é proveniente de resíduos orgânicos eventualmente da queima inicial.
Synthesis and thermal characterization of zirconium titanate pigments
(Springer, 2004-02) Costa, C. E. F.; Crispim, Samara C. L.; Lima, Severino Jackson Guedes; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Fernandes Júnior, Valter José; Araújo, Antônio Souza de; Santos, Ieda Maria Garcia dos; Souza, Antônio Gouveia de
The objective of this work was to obtain modern pigments based on zirconium titanate doped with nickel and cobalt using polymeric precursor method. Thermal evolution of ZrTiO4 phase was determined. After primary calcination, the material still exhibits two thermal composition events. Calcination was done between 500 and 1000°C, to morphological and structural characterization. Surface area decreased exponentially with temperature increase, while crystallite size increased. ZTCo and ZTNi pigments were applied on ceramic tiles and the good quality of the pigment was observed
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 dos
With 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
Thermal transformations of tile clay before and after kaolin addition
(Springer, 2004-02) Albuquerque, F. R.; Parente, B.; Lima, Severino Jackson Guedes; Paskocimas, Carlos Alberto; Silva, Elson Longo da; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dos; Fernandes Júnior, Valter José
The use of clays for ceramic filter processing may reduce its cost, leading to different applications, as water treatment. In this work, a low cost tile clay mixed with kaolin, for use in ceramic filters, were evaluated. Mineralogical and thermal changes occurring during sintering were characterized by differential thermal analysis, thermogravimetry, thermomechanical analysis and X-ray diffraction. An increase in the initial melting temperature of samples due to kaolin addition was observed. Mullite formation in kaolin was observed by DTA and in other samples by XRD. TMA analysis permitted the observation of pre-sintering step, around 850°C. This step is difficult to observe in other types of analysis
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 dos
In 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?
Yellow ZnxNi1−xWO4 pigments obtained using a polymeric precursor method
(Elsevier, 2007-05-25) Oliveira, André Luiz M. de; Ferreira, Jailson M.; Silva, Maria Rita de Cássia; Braga, Glauco Soares; Soledade, Luiz Edmundo Bastos; Aldeiza, M. A. Maurera Maria; Paskocimas, Carlos Alberto; Lima, Severino Jackson Guedes; Silva, Elson Longo da; Souza, Antônio Gouveia de; Santos, Ieda Maria Garcia dos
New tungstate-based ceramic pigments, displaying ZnxNi1 xWO4 stoichiometry, were obtained at low temperature using a polymeric precursor method. The powder precursors were milled in an attritor mill in an alcoholic medium and heat treated for 12 h, yielding homogeneous and crystalline powder pigments. Characterization (TG/DTA, XRD, IR and colorimetry) showed that mass loss increased with increasing Zn contents. Despite the presence of secondary phases and impurities, the wolframite phase was present in all samples. IR analysis revealed bands related to MeeO and [WO6]6 group stretching was observed. The intensity of the yellow color of the pigments increased with increasing amount of nickel

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Navegando por Autor "Souza, Antônio Gouveia de"