SILAS CARDOSO DOS SANTOS
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Artigo IPEN-doc 31171 Characterization of ceria powders as a continuous search for new rare-earth based materials for radiation dosimetry2024 - SANTOS, SILAS C. dos; RODRIGUES JUNIOR, ORLANDO; CAMPOS, LETICIA L.Background: Ceria (CeO2) belongs to rare-earth series and due to its profitable properties, presents a wide commercial use such as catalysis, energy, biological, biomedical, and pharmaceutical. The features of the starting materials in the form of free powders influence notably the processing, formation, as well as characteristics of the final structures\bodies obtained by colloidal processing. This study aims to characterize CeO2 powders. The results obtained are worthwhile data to advance toward new rare-earth based materials for radiation dosimetry. Methods: CeO2 powders were evaluated by the following techniques: PCS, SEM, XRD, FT-IR, EPR, IPC, and pycnometric density (ρ). The stability of particles in aqueous solvent was evaluated by zeta potential (ζ) determination. Results: CeO2 powders exhibited cubic C-type form, Fm-3m space group, a mean particle size (d50) of 19.3 nm, and a pycnometric density (ρ) of 7.01g.cm-3. Based on the results of zeta potential determination, CeO2 powders exhibited high stability at pH 6.4 with ζ- value of |34.0|mV. Conclusion: The evaluation of CeO2 powders was reported. The results presented and discussed in this study contribute to advance in the search of new rare-earth based materials for radiation dosimetry.Artigo IPEN-doc 31170 Alumina crucibles from free dispersant suspensions2024 - SANTOS, S.C.; MARTINS, A.S.; ARAUJO, T.L.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.Background: Powder technology provides conditions to control particle-particle interactions that drive the formation of final-component/material, which also includes the crystalline structure, microstructure and features. Alumina (Al2O3) is the most studied ceramic based material due to its useful properties, disposal, competitive price, and wide technological applicability. This work aims to produce alumina crucibles with controlled size and shape from free dispensant suspensions. These crucibles will be used as containers for the synthesis of new materials for radiation dosimetry. Methods: The Al2O3 powders were characterized by XRD, SEM, PCS, and EPR. The stability of alumina particles in aqueous solvent was evaluated by zeta potential determination as a function of pH. Alumina suspensions with 30 vol% were shaped by slip casting in plaster molds, followed by sintering at 1600oC for 2 h in an air atmosphere. Alumina based crucibles were characterized by SEM and XRD. Results: ɑ-Al2O3 powders exhibited a mean particle diameter size (d50) of 983nm. Besides, the stability of particles in aqueous solvent was achieved at a range of pH from 2.0-6.0, and from 8.5-11.0. EPR spectra revealed two resonance peaks P1 and P2, with g-values of 2.0004 and 2.0022, respectively. The as-sintered ɑ-alumina based crucibles presented uniform shape and controlled size with no apparent defects. In addition, the final microstructure driven by solid-state sintering revealed a dense surface and uniform distribution of grains. Conclusion: The ɑ-Al2O3 crucibles obtained by slip casting of free dispensant alumina suspensions, followed by sintering, exhibited mechanical strength, and controlled shape and size. These crucibles will be useful labwares for the synthesis of new materials for radiation dosimetry.Artigo IPEN-doc 28522 Microstructure evolution of yttria compacts by powder technology2021 - SANTOS, SILAS C.; RODRIGUES JUNIOR, ORLANDO; CAMPOS, LETICIABackground: Innovation in ceramic materials relies on the processing of powders. Yttria, also known as yttrium oxide, belongs to the rare-earth group (RE2O3 - RE from La to Lu, including Sc and Y). Due to the great properties and end-use of RE-based materials since agriculture until astronomy, studies on processing, sintering and microstructural evolution of RE-based materials are essential to provide new materials with improved characteristics. The aim of this paper is to obtain dense compacts of yttria by powder technology, in which the effect of sintering temperature on sample's microstructure is evaluated. Methods: Yttria powders (Y2O3) were characterized by Photon Correlation Spectroscopy (PCS), X-ray Diffraction (XRD), and Scanning Electron Microscopy (SEM). Cylindrical powder compacts were produced by uniaxial compaction, followed by hydrostatic compaction. Sintered samples obtained under sintering temperatures from 1350 to 1550ºC were evaluated by SEM, XRD, apparent density, and true density. Results: Cubic C-type yttria powders exhibited a mean particle size (d50) of 1.6μm, and morphology like acicular. Powder compacts (diameter x height) of 9.57mm ± 0.01 x 1.53mm ± 0.01 presented mean apparent density of 53.69% (based on free powder density). Sintered samples at 1550ºC exhibited the most densification, 65.0% related to the green density and 91.0% related to theoretical density, respectively. Conclusion: Yttria cylindrical compacts with dense microstructure, and symmetric dimensions were formed by powder technology from powders with a mean particle size of 6.51μm, by compaction methods (uniaxial and hydrostatic), followed by sintering. The most densification of samples was achieved by the sintering condition of 1550ºC for 2h, providing samples with a theoretical density of 91%. These results provide useful subsidies to advance toward full densification of yttria-based materials.Artigo IPEN-doc 25214 Synthesis, processing, and electron paramagnetic resonance response of Y1.98Eu0.02O3 micro rods2018 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.Innovating dosimetric materials, which includes design and development of new dosimetric materials based on rare earth oxides, is challenging. Yttrium oxide (Y2O3) is one of the most important sesquioxides and presents crystal characteristics that enable doping with rare earth ions, making it a promising material for radiation dosimetry. This paper reports on the development and measurement of Electron Paramagnetic Resonance (EPR) signal response for Y1.98Eu0.02O3 micro rods that have undergone facile low-pressure hydrothermal synthesis and bio-prototyping. Assynthesized powders with narrow sub-micrometer particle size distribution with d50 of 584 nm exhibited a reactive surface, which led to the formation of stable aqueous suspensions by controlling the surface charge density of particles through alkaline pH adjustment. Ceramic samples with dense microstructure were formed by sintering at 1600 ºC for 4h at ambient atmosphere. Y1.98Eu0.02O3 micro rods were irradiated using a 60Co source with doses from 1 to 100 kGy, and EPR spectra were measured at room temperature in X-band microwave frequencies. Sintered samples exhibited linearity of the main EPR signal response from 10 Gy to 10 kGy. Supralinearity was observed for higher doses, which is possibly ascribed to formation of more defects. Using europium as a dopant enhanced the EPR signal of yttrium rods remarkably, due to 4f–4f transitions of the Eu3+ ion. These innovative findings make europium-doped yttrium oxide a promising material for radiation dosimetry.