Navegando por Autor "Medeiros, P. N."

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Effect of different starting materials on the synthesis of Ba0.8Ca0.2TiO3
(SpringerOpen, 2015-01-31) Medeiros, P. N.; Araújo, Vinícius Dantas de; Marques, Ana Paula de Azevedo; Tranquilin, Ricardo Luis; Paskocimas, Carlos Alberto; Delmonte, Maurício Roberto Bomio; Varela, José A.; Silva, Elson Longo da; Motta, Fabiana Villela da
Literature has reported the synthesis of barium calcium titanates by various synthesis methods such as solid state reaction, co-precipitation and polymer precursors. These compounds are usually obtained using calcium carbonate (CaCO3), barium carbonate (BaCO3) and titanium oxide as starting materials. This study investigated the effect of different starting reagents on the synthesis of Ba0.8Ca0.2TiO3 (BCT) by complex polymerization method (CPM). Two sets of starting precursors were used: titanium citrate, CaCO3 and BaCO3, and titanium citrate and Ba1−x Ca x CO3 solid solution precursor. Samples were crystallized at a temperature range from 400 °C to 700 °C for different time. The obtained powders were characterized by X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA), and Raman and infrared spectroscopy. The infrared spectroscopy indicated that the chelation processes of Ba, Ca, Ti and CA ions are very similar. The results showed that the use of CaCO3 and BaCO3 or Ba1−x Ca x CO3 solid solution as precursors does not affect the final properties of BCT powders obtained by CPM
Fast and simultaneous doping of Sr0.9−x−y−zCa0.1In2O4:(xEu3+, yTm3+, zTb3+) superstructure by ultrasonic spray pyrolysis
(Elsevier, 2019-09) Paskocimas, Carlos Alberto; Santiago, Anderson de Azevedo Gomes; Lovisa, Laura Ximena; Medeiros, P. N.; Li, Maximo Siu; Carreño, Neftalí Lênin Villarreal; Silva, Elson Longo da; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
In the present work, Sr0.9−x−y−zCa0.1In2O4:(xEu3+, yTm3+, zTb3+) particles were synthesized by the ultrasonic spray pyrolysis (USP) method to obtain a single-phase white phosphorus formed by six different cations in solution within the lattice (superstructure). The samples were also structurally and morphologically characterized by X-ray diffraction (XRD) techniques and by field emission scanning electron microscopy (FE-SEM). The photoluminescent behavior and the characteristics of the emitted colors were studied by the variation in the codoping of the rare earth elements. The Sr0.9Ca0.1In2O4 sample showed a near blue color emission, but all codoped samples showed emission in white with very close chromaticity coordinates to the standard white (x = 0.33 and y = 0.33). The Tm3+ → Tb3+ (ET1), Tm3+ → Eu3+ (ET2) and Tb3+ → Eu3+ (ET3) Energy Transfers were proposed and are considered necessary for adjusting and controlling the desired color properties
Influence Ca-doped SrIn2O4 powders on photoluminescence property prepared one step by ultrasonic spray pyrolysis
(Elsevier, 2018-05-30) Medeiros, P. N.; Santiago, Anderson de Azevedo Gomes; Ferreira, Erik Alexander Cunha; Li, Maximo Siu; Silva, Elson Longo da; Delmonte, Maurício Roberto Bomio; Motta, Fabiana Villela da
Crystalline Ca-doped SrIn2O4 structures were prepared by a rapid and efficient Ultrasonic Pyrolysis Spray (USP) method. The Sr1-xCaxIn2O4 (x = 0, 0.1, 0.2, 0.3, 0.4 and 1 mol %) samples were obtained by in a single step at a temperature of 1050oC for 1 min for the formation of particles. The powders were characterized by X-ray diffraction (XRD), field emission electron microscopy (SEM-FEG), optical diffuse reflectance and photoluminescence (PL) measurements. All diffraction peaks present in XRD patterns could be indexed to the orthorhombic structure and that with calcium percentage increments indicates the substitution of Ca2+ in the Sr2+ sites promotes a decrease in its lattice parameters of the structure. MEV-FEG images show that the Sr1- xCaxIn2O4 particles have a spherical predominance, with a porous surface in the form of foam for x = 0 and a surface with low roughness and low porosity with an increase in the percentage of Ca2+ ion, especially for the 1 mol % of Ca2+. The gap energy varied between 4.56 eV and 4.86 eV, being influenced by the structural modifications motivated by increase of Ca2+ ion contained in the SrIn2O4 matrix. The PL emission spectrum of the samples presents a broad band behavior with emission intensity predominant in the blue-green region, having the sample with x = 0.1 the highest PL intensity. The chromaticity coordinates were calculated for the sample based on the PL spectrum and coordinates x and y show that the samples have blue emission. Ultrasonic spray pyrolysis was an effective technique for Ca-doped SrInO4 powder production using short production times with hold great potential for photoluminescent emitters
Influence of variables on the synthesis of CoFe2O4 pigment by the complex polymerization method
(SpringerOpen, 2015-05-30) Medeiros, P. N.; Gomes, Yara Feliciano; Delmonte, Maurício Roberto Bomio; Santos, I. M. G.; Silva, M. R. S.; Paskocimas, Carlos Alberto; Li, M. S.; Motta, Fabiana Villela da
Synthetic inorganic pigments are most widely used in ceramic applications due to their excellent chemical and thermal stability and their lower toxicity to both human and environment as well. In the present work, black ceramic pigment CoFe2O4 has been synthesized by the complex polymerization method (CPM) with good chemical homogeneity. In order to study the influence of variables on the process of obtaining pigment through CPM, 2(5-2) fractional factorial design with resolution III was used. The variables studied in the mathematical modeling were: citric acid/metal concentration, pre-calcination time, calcination temperature, calcination time, and calcination rate. Powder pigments were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and UV-visible (UV-Vis) spectroscopy. Based on the results, the formation of cobalt ferrite phase (CoFe2O4) with spinel structure was verified. The color of pigments obtained showed dark shades, from black to gray. The model adjusted to the conditions proposed in this study due to the determination coefficient of 99.9% and variance (R 2) showed that all factors are significant at the confidence level of 95%

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Navegando por Autor "Medeiros, P. N."