VINICIUS RIBAS DE MORAIS

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Novel method for the synthesis of Dy-doped yttrium disilicate phosphors
2018 - YAMAGATA, C.; LEME, D.R.; MORAIS, V.R.
Yttrium disilicate (Y2Si2O7) displays interesting structural properties because of its high refractoriness and stability in oxidizing environments. With its wide band gap and excellent thermal and chemical stability, it has been shown to be one of the most efficient host lattices for rare earth ions, which substitute Y3+ ions. When it is doped with different metallic ions, yttrium silicates exhibit attractive luminescent properties for potential applications, such as plasma displays, laser materials and high-energy phosphors. The use of solid-state reaction for yttrium disilicate synthesis shows disadvantages such as long times and temperatures of processing and formation of undesirable by-products. The objective of this work was to obtain silica (SiO2) nanoparticles by surfactant-assisted sol-gel process, using sodium silicate (Na2SiO3) as Si precursor, and its application on the synthesis of yttrium disilicate-based (Y2Si2O7) phosphors. Yttrium hydroxide was added to obtained silica nanoparticles, by precipitation from yttrium nitrate. Two precursors of yttrium disilicate were prepared: un-doped and doped with dysprosium 2,5 at %, (Y1,95Dy0,05Si2O7). The obtained powders were characterized by X-ray diffraction (XRD), to identify the polymorphic phases of yttrium disilicate, scanning electron microscopy (SEM), to observation of morphology. and luminescence spectroscopy. It was observed that ?-phase of Y2Si2O7 was obtained at 1300°C and showed sharper luminescence peaks in comparison with ?-phase. 7th International Congress on Ceramics & 62º Congresso Brasileiro de Cerâmica June 17-21, 2018, Foz do Iguaçu - PR - Brazil 626
Preparation of Dy3+-doped calcium magnesium silicate phosphors by a new synthesis method and its luminescence characterization
2018 - MORAIS, VINICIUS R. de; LEME, DANIEL de R.; YAMAGATA, CHIEKO
Recently, rare-earth doped alkaline earth silicates have been researched extensively as a new generation of afterglow phosphors. Compared with the conventional sulphide materials used for this purpose, silicates yield luminescence with longer duration time and higher bright, as well as improved chemical stability and lower cost. In the present work, Dy-doped calcium magnesium silicate phosphors were prepared by joining the methods sol-gel and co precipitation. Silica gel was obtained from sodium silicate solution. Ca, Mg and Dy hydroxides, precipitated from chloride solutions with NaOH, were added to the obtained gel. After washing for removal of Cl- ions, the product was annealed at 1000°C for 2 hours. XRD results confirmed the formation of diopside phase (CaMgSi2O6). The product was later characterized by SEM and luminescence spectroscopy.
Synthesis and characterization of bioactive ceramic in CaO-MgO-SiO2 system
2018 - LEME, D.R.; MORAIS, V.R.; RODAS, A.C.D.; HIGA, O.Z.; YAMAGATA, C.
Na2SiO3 solution and chloride solutions of calcium and magnesium were used as raw materials. HCl was added to Na2SiO3 solution resulting in gel of silica. In order to obtain a mixture of Si gel, Ca2+ and Mg2+, calcium and magnesium solutions were blended into the gel. After adding NaOH to the mixture, Ca2+ and Mg2+ ions precipitated as hydroxides. Subsequently, it was dried to attain the ceramic precursor powder, which was calcined at 900 ºC for 1h, compacted into a pellet form and sintered at 1200 ºC for 2h. The ceramic body was characterized by SEM, XRD and FTIR. In vitro test for bioactivity verification was performed in SBF. A surface deposition of hydroxyapatite on the ceramic body was observed after 3 days. The cytotoxicity test revealed that the material has cell viability above 70%, meaning that it is not toxic for the cells, according to ISO 10993-5 standard.
Novel method for the synthesis of Dy-doped yttrium disilicate phosphoros
2018 - MORAIS, V.R.; REZENDE, D.L.; YAMAGATA, C.
The complex high temperature polymorphism (Y, α, β, γ and δ structures) of yttrium disilicate (Y2Si2O7) naturally lead to relatively broad emission, originating from ions placed in different symmetry sites, for example, the replacing of Y3+ by rare earth ions. Y2Si2O7 as the host lattice shows a high thermal and chemical stability compared with other well-studied phosphors such as ZnS and CdS. When doped with different metallic ions, yttrium silicates exhibit attractive luminescent properties for potential applications, such as plasma displays, laser materials and high-energy phosphors. The sol-gel technique provides an available method to prepare ceramic powders, with higher purity and homogeneity compared to the conventional solid-state reaction of mixed oxides. In the present work, a novel sol-gel and co-precipitation combined method has been proposed for synthesis of RE3+ doped Y2Si2O7 (RE=Dy). Silica nanoparticles were obtained by surfactant-assisted sol-gel process, using sodium silicate (Na2SiO3) as precursor, and then Y3+ and Dy3+ ions were precipitated over these particles. The RE3+:Y2Si2O7 obtained product was analyzed by SEM, XRD and luminescence spectroscopy. Crystalline Y2Si2O7 was obtained at lower temperatures compared with traditional methods. The α-phase was obtained at 1100 and 1200°C, and β-phase at 1300°C. Comparing photoluminescence spectra of α and β-phases, the later showed higher intensity luminescence peaks.
Silicato de cálcio e magnésio dopado com terras raras para aplicação como material luminescente
2018 - MORAIS, V.R.; LEME, D.R.; YAMAGATA, C.
Nos últimos anos, silicatos de metais alcalinos dopados com terras raras têm sido fortemente pesquisados como uma nova geração de fósforos com persistência luminescente. Comparados com os sulfetos convencionalmente utilizados para esse fim, silicatos apresentam luminescência com maior brilho e duração, alem de maior estabilidade química e menor custo. No presente trabalho, fósforos à base de silicatos de cálcio e magnésio (CaxMgSi2O5+x), dopados com Dy3+ foram preparados pela combinação dos métodos sol-gel e coprecipitação. Géis de silica foram obtidos a partir de solução de silicato de sódio. Hidróxidos de Ca, Mg and Dy, precipitados a partir de soluções clorídricas com NaOH, foram adicionados ao gel de sílica. Após lavagem com água destilada para remoção de ions Cl-, o produto foi seco em estufa e calcinado a 1000°C por 2 horas. Os resultados de DRX confirmaram, após a calcinação, a formação da fase diopsita (CaMgSi2O6), fase adequada como host para material luminescente. No espectro de emissão observaram-se picos em 479, 496, 577 e 593 nm, que correspondem, respectivamente, as transições 4F9/2-6H15/2 e 4F9/2-6H13/2 do íon Dy3+. A morfologia do pó foi observada por MEV.
Síntese, caracterização e avaliação da bioatividade da vitrocerâmica no sistema CaO-MgO-SiO2 para engenharia de tecido ósseo
2018 - LEME, D.R.; MORAIS, V.R.; RODAS, A.C.D.; HIGA, O.Z.; MELLO-CASTANHO, S.R.H.; YAMAGATA, C.
Depois da descoberta do bioglass® por Larry Hench, os vitrocerâmicos são estudados por apresentarem bioatividade. Entre as cerâmicas utilizadas para aplicação ortopédica, a do sistema CaO-MgO-SiO2 recebe importante atenção por apresentar propriedades mecânicas melhoradas pela presença do Mg que também auxilia na integração deste material ao tecido vivo. Sabe-se que várias técnicas de síntese podem ser aplicadas na obtenção dos pós cerâmicos de CaO-MgO-SiO2, por exemplo, reação no estado sólido, spray pirólise, coprecipitação e sol-gel. Neste trabalho, gel de sílica foi obtido pelo método sol-gel por reação de catálise ácida, com HCl em solução de silicato de sódio. Em seguida, soluções clorídricas de cálcio e magnésio foram adicionadas para obter uma mistura de gel de Si, Ca2+ e Mg2+. Na mistura, adicionou-se NaOH para precipitar Ca e Mg na forma de hidróxidos. O produto foi filtrado, lavado e seco para obter o pó cerâmico precursor. Após calcinação do pó a 900ºC por 1h, este foi prensado na forma de pastilha e sinterizado a 1200ºC por 2h. O corpo cerâmico obtido foi caracterizado pelas técnicas DRX, FTIR e MEV. Os difratogramas revelaram a presença da fase cristalina diopside como majoritária. A bioatividade do material foi verificada após três dias imersa em SBF (simulated body fluid) e comprovada por FTIR e MEV. Teste de citotoxicidade confirmou viabilidade celular acima de 70%, o que segundo a norma ISO 10993-5 é sancionado como não citotóxico.