SILAS CARDOSO DOS SANTOS

SILAS CARDOSO DOS SANTOS

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Advances in colloidal processing of rare earth particles
2018 - SANTOS, SILAS C.; RODRIGUES, ORLANDO; CAMPOS, LETICIA L.
Abstract: Background: New insights into materials science provide development of smart nano/micro structured materials for advanced applications. Rare earth includes a set of chemical elements (from La to Lu, including Sc and Y) with unique properties, the use of which is evidenced by luminescence applications. Colloidal processing offers great possibilities to obtain smart materials by controlling inter-particle forces, as well as their evolution during ceramic processing. The present article reports a review on colloidal processing with emphasis on rare earth powders. A general view about rare earths properties, including scientific investigations and applications are also presented. Methods: General view on rare earth sources, classification, properties, studies, and applications are reported. Besides, a review on colloidal processing covering particle characteristics, inter- particle forces, dispersion methods, rheology of suspensions, shaping process, drying-sintering stage, and microstructure formation is reported. Results: Yttria is the most used rare earth oxide in phosphors applications (70%). Synthesis routes imply on powder properties. Particle characteristics as size, shape, density, and surface area are important parameters for colloidal processing. The control of inter- particle forces by zeta potential evaluation and using dispersion methods provide conditions to prepare stable suspensions. Consolidation of colloidal particles into a desired shape depends on both viscosity and rheological behavior of suspensions. Drying-sintering conditions are effective on microstructure formation and component characteristics. Bio-prototyping is a low cost method, which provides components with complex shape and cellular architecture. Conclusion: Rare earths exhibit remarkable properties, being applied in diverse technological end-use. Colloidal processing provides opportunities to form smart materials since synthesis of colloids until development of complex ceramic components by shaping methods and thermal treatment. Even though colloidal processing is quite mature, investigations on rare earths involving inter- particle forces, shaping, drying-sintering stage, and microstructure formation are very scarce.
Bio-prototyping of europium-yttria based rods for radiation dosimetry
2017 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.
The application of solid state dosimeters in radiation protection has grown significantly as consequence of advances in the development of dosimetric materials using rare earths. The conception of new dosimetric materials concerns synthesis methods, which control the evolution of material structure, including further processing steps as, shaping, drying, and sintering. The present study reports a full bio-prototyping approach to produce europium doped yttria rods with potential application in radiation dosimetry. Ceramic particles synthesized by hydrothermal route were characterized by Photon Correlation Spectroscopy (PCS), X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM). The effect of europium on promoting electronic defects in yttria host was evaluated by Electron Paramagnetic Resonance (EPR). Low pressure hydrothermal synthesis led to formation of rounded particles with mean diameter of 410 nm. Aqueous suspensions with 20 vol% of particles prepared at pH 10, and 0.2 wt% binder exhibited apparent viscosity of 213 mPa s, being suitable for bio-prototyping of rods. Sintering of shaped samples at 1600 degrees C for 4 h provided formation of dense ceramic rods. Europium-yttria rods containing 5 at.% Eu exhibited the most intense EPR response.
Processing, microstructure and thermoluminescence response of biomorphic yttrium oxide ceramics
2016 - SANTOS, S.C.; YAMAGATA, C.; CAMPOS, L.L.; MELLO-CASTANHO, S.R.H.
The present work reports a fast-direct bio-prototyping process using Luffa Cylindrica vegetable sponge to produce biomorphic yttrium oxide ceramics with reticulated-porous architecture and thermoluminescence response. Processing parameters as rheology of yttrium oxide suspensions, bio-template surface treatment and thermal decomposition of bio-template were investigated. Shear thinning suspensions of 30 vol% yttrium oxide with apparent viscosity of 243mPa.s provided a successful impregnation of samples, whereby bio-templates with smooth ceramic layer and hierarchical reticulated architecture were formed. By thermal treatment at 1600 degrees C for 2 h biomorphic yttrium oxide ceramics with porous microstructure and TL response at 150 degrees C and lambda=550 nm were produced. The proposed fast direct bio-prototyping process is suitable for the production of ceramic components with complex shape and demonstrates potential for general applicability to any bio-template. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Processing and thermoluminescent response of porous biomorphic dysprosium doped yttrium disilicate burner
2016 - SANTOS, S.C.; YAMAGATA, C.; CAMPOS, L.L.; MELLO CASTANHO, S.R.H.
Rheological behaviour of yttria aqueous suspensions for impregnation method
2010 - SANTOS, S.C.; YAMAGATA, C.; MELLO CASTANHO, S.R.H.
Yttrium disilicate stability in aqueous medium
2013 - SANTOS, S.C.; ACCHAR, W.; SILVA, A.C.; YAMAGATA, C.; MELLO CASTANHO, S.R.H.
Caracterização físico-química de pôs de oxido de ítrio
2008 - SANTOS, S.C.; MELLO CASTANHO, S.R.H.
A ítria (Y2O3) é utilizada em diversas aplicações tecnológicas, tais como fósforos para displays, lasers de estado sólido, televisores de alta definição, displays de plasma, tubos de raios catódicos, também como estabilizante estrutural da zircônia (ZrO2) e aditivo de sinterização para diversos materiais cerâmicos covalentes. O conhecimento de suas características físico-químicas e propriedades microestruturais fornecem importantes subsídios para um adequado processamento e controle dos produtos finais à base de óxido de ítrio. Este trabalho avalia as características físico-químicas dos pós de ítria comercial, comparando-se as características antes e após moagem em moinho atritor, utilizando-se as técnicas de difração de raios X (DRX), microscopia eletrônica de varredura (MEV), determinação da área de superfície específica (BET), entre outras. Os pós moídos por 3 horas apresentaram os melhores resultados.
Morphology evolution of yttria porous ceramics during replica processing
2011 - SANTOS, S.C.; SILVA, A.C.; MELLO CASTANHO, S.R.H.
Processamento coloidal de componentes ceramicos para queimadores de gas
2010 - SANTOS, SILAS C. dos
A ítria vem sendo muito utilizada como material luminescente e estrutural resistente a altas temperaturas, devido às suas excelentes características ópticas e refratárias. No processamento coloidal da ítria, o controle da estabilidade da suspensão consiste em uma importante etapa quando se objetiva produzir componentes reprodutivos, com densidade controlada, microestrutura homogênea e estabilidade estrutural. Desta maneira, os estudos envolvendo o comportamento de superfície, as condições de estabilidade das suspensões e o comportamento frente às condições de conformação (fluxo), fornecem importantes subsídios para controle dos processos na fabricação de componentes cerâmicos para queimadores de gás. Neste sentido, realizaram-se estudos sobre o comportamento de superfície, de estabilidade e reológico de suspensões aquosas de ítria e do concentrado de terras raras contendo ítria a fim de adequá-las para o processo de conformação por impregnação, onde foram testados diferentes materiais orgânicos como matrizes de réplica, para a confecção de membranas porosas para queimadores de gás. Neste estudo foram avaliados os parâmetros como: pH do meio, concentrações de dispersante, sólidos e ligante na estabilidade e no comportamento ao fluxo das suspensões cerâmicas, e também os aspectos dos distintos materiais orgânicos selecionados como matrizes de réplica para impregnação com as suspensões cerâmicas otimizadas. Os resultados obtidos indicam que se pode confeccionar membranas cerâmicas porosas pelo método de réplica a partir das suspensões aquosas de ítria e do concentrado de terras raras contendo ítria, utilizando-se pH alcalino, polieletrólito aniônico e uma tela mista de nylon-algodão como matriz de réplica.