SILAS CARDOSO DOS SANTOS

SILAS CARDOSO DOS SANTOS

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Characterization of ceria powders as a continuous search for new rare-earth based materials for radiation dosimetry
2024 - 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.
Alumina crucibles from free dispersant suspensions
2024 - 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.
Effect of thulium on promotion of dose-response behaviour of yttria based rods by Electron Paramagnetic Resonance
2024 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.
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.
A glance at dysprosium oxide free powders
2023 - SANTOS, SILAS C.; RODRIGUES JUNIOR, ORLANDO; CAMPOS, LETICIA L.
Background: Dysprosium oxide (Dy2O3) gathers a set of profitable properties with a wide range of applications, including energy and astronomy. Particular characteristics directly influence the formation and features of materials by colloidal processing. The main purpose of this paper is to carry out a powder characterization of Dy2O3particles. The findings reported are worthwhile parameters to advance in the formulation of new smart materials for radiation dosimetry. Methods: Dy2O3 powders were characterized by XRD, PCS, SEM, pynometric density (ρ), FTIR, ICP, EPR, and zeta potential (ζ). Results: The powdered samples exhibited as main features a cubic C-type structure following the RE-polymorphic diagram, a mean particle size distribution with d50 of 389nm, and pynometric density of 7.94g.cm-3. The EPR spectra revealed three distinct peaks, p1, p2, and p3, with the following g values: 2.3121, 2.1565, and 2.1146. In addition, the nanoparticles presented high stability at pH 5.5 and a ζ-value of |49.7|mV. Conclusion: The powder characterization of Dy2O3 powders was reported. The results achieved in this study may be considered worthwhile parameters to advance in the formulation of Dy2O3- based materials for radiation dosimetry.
Synthesis of thulium-yttria nanoparticles with EPR response
2022 - SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L.
Approaches to form new materials for radiation dosimetry are essential to enhance quality assurance and quality improvement practices based on radiation protection concept. The present work reports a hydrothermal synthesis based on a relative low temperature and pressure to form thulium-yttria nanoparticles with electron paramagnetic resonance response. Thulium-yttria nanoparticles were prepared and characterized by XRD, SEM, PCS, and EPR. According to results, the hydrothermal method provided thulium-yttria nanoparticles with cubic C-type structure, mean particle size (d50) less than 160nm, and EPR response. The EPR spectra of powders exhibited two resonance peaks p1 and p2 recorded at 350 and 160mT, respectively. The enhancement of the EPR response of yttria by the use of thulium as a dopant provide meaningful parameters to advance in the formation of new rare earth-based materials for radiation dosimetry.
Evaluation of rare-earth sesquioxides nanoparticles as a bottom-up strategy toward the formation of functional structures
2022 - SANTOS, SILAS C. dos; RODRIGUES JUNIOR, ORLANDO; CAMPOS, LETICIA L.
Background: The strategy to form functional structures based on powder technology relies on the concept of nanoparticles characteristics. Rare-earth sesquioxides (RE2O3; RE as Y, Tm, Eu) exhibit remarkable properties, and their fields of application include energy, astronomy, environmental, medical, information technology, industry, and materials science. The purpose of this paper is to evaluate the characteristics of RE2O3 nanoparticles as a bottom-up strategy to form functional materials for radiation dosimetry. Methods: The RE2O3 nanoparticles were characterized by the following techniques: XRD, SEM, PCS, FTIR, ICP, EPR, and zeta potential. Results: All RE2O3 samples exhibited cubic C-type structure in accordance with the sesquioxide diagram, chemical composition over 99.9 %, monomodal mean particle size distribution, in which d50 value was inferior to 130 nm. Among all samples, only yttrium oxide exhibited an EPR signal, in which the most intense peak was recorded at 358mT and g 1.9701. Conclusion: Evaluating nanoparticle characteristics is extremely important by considering a bottom-up strategy to form functional materials. The RE2O3 nanoparticles exhibit promising characteristics for application in radiation dosimetry.
A glance on rare earth oxides
2021 - SANTOS, SILAS; RODRIGUES, ORLANDO; CAMPOS, LETICIA
Background: Innovation mission in material science requires new approaches to form functional materials, wherein the concept of its formation begins in nano/micro scale. Rare earth oxides with general form (RE2O3; RE from La to Lu, including Sc and Y) exhibit particular proprieties, being used in a vast field of applications with high technological content since agriculture to astronomy. Despite their applicability, there is a lack of studies on the surface chemistry of rare earth oxides. Zeta potential determination provides key parameters to form smart materials by controlling interparticle forces, as well as their evolution during processing. This paper reports a study on zeta potential with emphasis on rare earth oxide nanoparticles. A brief overview of rare earths, as well as zeta potential, including sample preparation, measurement parameters, and the most common mistakes during this evaluation are reported. Methods: A brief overview of rare earths, including zeta potential, and interparticle forces are presented. A practical study on zeta potential of rare earth oxides - RE2O3 (RE as Y, Dy, Tm, Eu, and Ce) in aqueous media is reported. Moreover, sample preparation, measurement parameters, and common mistakes during this evaluation are discussed. Results: Potential zeta values depend on particle characteristics such as size, shape, density, and surface area. Besides, the preparation of samples, which involves electrolyte concentration and time for homogenization of suspensions, is extremely valuable to get suitable results. Conclusion: Zeta potential evaluation provides key parameters to produce smart materials through which interparticle forces can be controlled. Even though zeta potential characterization is mature, investigations on rare earth oxides are very scarce. Therefore, this innovative paper is a valuable contribution to this field.
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.