SILAS CARDOSO DOS SANTOS

SILAS CARDOSO DOS SANTOS

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Correlation between zeta potential and electron paramagnetic resonance of thulium, europium co-doped yttria based suspensions
2024 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.
The formation of advanced ceramic components with homogeneous microstructure and functional characteristics demands a suitable control of particle dispersion. Thus, the characterization of particle stability as immersed in a liquid medium is important. The present paper reports an approach to evaluate the stability of europium, thulium co-doped yttria (YET) nanoparticles by a correlation between zeta potential and Electron Paramagnetic Resonance (EPR) techniques. Based on results, YET suspensions exhibited high stability apart from pH 10, while their isoelectric point presented a slight variation from pHIEP 8.5 to 9.2 according to thulium content 0 and 2 at.%, respectively. The peak-to-peak amplitude of EPR spectra of the YET suspensions increased as pH shifted toward alkaline condition, following zeta potential curves features. The present achievements are very useful parameters to form stable suspensions based on rare-earth oxides and to advance toward new materials for radiation dosimetry.
Building up europium thulium co-doped yttria nanoparticles with electron paramagnetic resonance response by colloidal synthesis
2023 - SANTOS, SILAS C. dos; RODRIGUES JR., ORLANDO; CAMPOS, LETICIA L.
In the radiation dosimetry field the research for new materials is a continuos demand with the aim to provide highly improvement procedures where ionizing radiation is used. Considering this challenge, the present work reports the colloidal synthesis of europium-thulium-co-doped yttria powders (YET) and evaluates the dopants effect on the promotion of EPR response of yttria. The powdered compositions prepared with up to 2at.%Tm and 2at.%Eu (at.%, atomic percentage) were evaluate by XRD, PCS, SEM, and EPR. Based on the results, the proposed synthesis method provided ceramic powders with cubic C-type form and mean particle size (d50) less than 160nm. The most significant EPR dose-response was noticed for the powdered composition prepared with 0.5at. %Tm (YET0.5) as irradiated with 5kGy (60Co). These findings are key parameters to advance toward the formation of new materials for radiation dosimetry.
Microstructure evolution of yttria compacts by powder technology
2021 - SANTOS, SILAS C.; RODRIGUES JUNIOR, ORLANDO; CAMPOS, LETICIA
Background: 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.
EPR response of yttria micro rods activated by europium
2018 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.
Rare earth (RE) materials present excellent properties, which importance is recognized worldwide. Innovation approaches in energy, medicine, communication, transportation, militarism, and radiation dosimetry consist in RE based materials. As yttrium oxide (Y2O3) exhibits intrinsic lattice characteristics that enable doping with others RE elements (Y2O3:RE), new materials with promising characteristics can be developed. This work aims to evaluate EPR response of europium-yttria (Y2O3:Eu) rods obtained by bio-prototyping. Ceramic rods containing up to 10 at.%Eu were irradiated with gamma doses from 0.001 to 150 kGy and evaluated by Electron Paramagnetic Resonance (EPR) at room temperature with X-band EPR. Based on results, Y2O3:Eu rods with 2 at.%Eu exhibited the most significant response, in which linear behavior arose from 0.001 up to 50 kGy. Fading and thermal annealing evaluations revealed that 2 at%.Eu improved dosimetric characteristics of yttria remarkably. These innovative findings afford that Y2O3:Eu is a promising material for radiation dosimetry.
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.