Abstract: 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.

Palavras-Chave: biotechnology; europium; rare earths; dosimetry; yttrium; ceramics; processing

SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L. Bio-prototyping of europium-yttria based rods for radiation dosimetry. Materials Chemistry and Physics, v. 199, p. 557-566, 2017. DOI: 10.1016/j.matchemphys.2017.07.063. Disponível em: http://repositorio.ipen.br/handle/123456789/27875. Acesso em: $DATA.

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Abstract: The development of new dosimetric materials is essential for the safe and effective use of nuclear technology. In the present study, an eco-friendly bio-prototyping approach was developed for preparing thulium-yttria microceramics with potential applications in radiation dosimetry. Micro-powder compacts were obtained by casting colloidal thulium-yttria suspensions prepared with 20 vol% particles in thin-walled tube templates. Samples were sintered at 1600 °C for 2 h under the environmental pressure and atmosphere to obtain thulium-yttria microceramics with dimensions of 3.33 ± 0.01 mm × 2.27 ± 0.01 mm (height × diameter), as well as a cubic C-type structure, pycnometric density of 4.79 g cm−3 (95.61% theoretical density), and surface microstructure comprising hexagon-like grains bonded at the boundaries. The use of thulium as an activator of yttria greatly improved the electron paramagnetic resonance (EPR) response of the microceramics, where the main EPR peak (p1) was recorded at 351.24 mT and the g factor was 2.0046. The innovative findings obtained in this study may facilitate the production of new solid state dosimeters.

Palavras-Chave: colloids; ceramics; dosimetry; rare earths; yttrium; thulium oxides

SANTOS, S.C.; RODRIGUES JUNIOR, O.; CAMPOS, L.L. Colloidal processing of thulium-yttria microceramics. Journal of Physics and Chemistry of Solids, v. 161, p. 1-10, 2022. DOI: 10.1016/j.jpcs.2021.110420. Disponível em: http://repositorio.ipen.br/handle/123456789/32663. Acesso em: $DATA.

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Abstract: Objectives. During the last decades, several changes of paradigm have modified our view on how biomaterials' surface characteristics influence the bioresponse. After becoming aware of the role of a certain microroughness for improved cellular contact and osseointegration of dental titanium implants, the likewise important role of surface energy and wettability was increasingly strengthened. Very recently, synergistic effects of nanoscaled topographical features and hydrophilicity at the implant/bone interface have been reported. Methods. Questions arise about which surface roughness and wetting data are capable to predict the bioresponse and, ultimately, the clinical performance. Current methods and approaches applied for topographical, wetting and surface energetic analyses are highlighted. Current knowledge of possible mechanisms explaining the influence of roughness and hydrophilicity at the biological interface is presented. Results. Most marketed and experimental surfaces are based on commonly available additive or subtractive surface modifying methods such as blasting, etching or anodizing. Different height, spatial, hybrid and functional roughness parameters have been identified as possible candidates able to predict the outcome at hard and soft tissue interfaces. Likewise, hydrophilic implants have been proven to improve the initial blood contact, to support the wound healing and thereby accelerating the osseointegration. Significance. There is clear relevance for the influence of topographical and wetting characteristics on a macromolecular and cellular level at endosseous implant/biosystem interfaces. However, we are still far away from designing sophisticated implant surfaces with the best possible, selective functionality for each specific tissue or cavity interface. Firstly, because our knowledge of the respective surface related reactions is at best fragmentary. Secondly, because manufacturing of multi-scaled complex surfaces including distinct nanotopographies, wetting properties, and stable cleanliness is still a technical challenge and far away from being reproducibly transferred to implant surfaces. (C) 2017 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Palavras-Chave: biological materials; implants; dentistry; ceramics; zirconium; yttrium

MIRANDA, RANULFO B. de P.; MIRANDA JUNIOR, WALTER G.; LAZAR, DOLORES R.R.; USSUI, VALTER; MARCHI, JULIANA; CESAR, PAULO F. Effect of titania content and biomimetic coating onthe mechanical properties of the Y-TZP/TiO2 composite. Dental Materials, v. 34, n. 2, p. 238-245, 2018. DOI: 10.1016/j.dental.2017.11.003. Disponível em: http://repositorio.ipen.br/handle/123456789/28455. Acesso em: $DATA.

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Abstract: Since the first report several years ago on pressureless sintering of yttria-stabilized zirconia with several seconds at relatively low temperatures by application of an electric field, an increasing number of scientific reports have been published on sintering ion conducting, semiconducting and insulating polycrystalline electroceramics. The electric field-assisted sintering consists in applying an electric field either during heating up or under isothermal conditions at temperatures well below the ones applied during conventional sintering. Besides the lower temperatures, shorter times are required to achieve full densification without considerable grain growth, evidencing the potential of this technique for obtaining functional electroceramics with improved mechanical and electrical properties at lower costs. Even though some mechanisms have been suggested, the description of the phenomenon at the microscopic level leading to full densification with seconds remains a challenge. We report in situ electrochemical impedance spectroscopy of an ionic conductor (ZrO2: 8 mol% Y2O3), a proton conductor (BaCe0.8Zr0.1Y0.1O3-delta) and a semiconductor (SnO2: 0.5 mol% MnO2) performed during conventional and electric field-assisted sintering experiments. Attention is also directed on the description of the experimental setups and procedures and to the evaluation of microstructural details by scanning electron microscopy. The analysis of the in situ impedance spectroscopy diagrams under heating (before either conventional or electric field-assisted sintering) and under cooling (after) provides evidence of densification with pore elimination and welding of grains. Prospects for future experimental and simulation research work are outlined.

Palavras-Chave: sintering; electric fields; impedance; spectroscopy; yttrium; zirconium oxides; dilatometry; ceramics

MUCCILLO, R.; MUCCILLO, E.N.S. Electric field assisted sintering of electroceramics and in situ analysis by impedance spectroscopy. Journal of Electroceramics, v. 38, n. 1, p. 24-42, 2017. DOI: 10.1007/s10832-016-0054-x. Disponível em: http://repositorio.ipen.br/handle/123456789/27710. Acesso em: $DATA.

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Abstract: ZrO2: 3 mol % Y2O3 (3YSZ) polycrystalline pellets were sintered at 1400 C and by applying an alternating current (AC) electric field at 1000 C. An alumina sample holder with platinum wires for connecting the sample to a power supply was designed for the electric field-assisted sintering experiments. The apparent density was evaluated with the Archimedes technique, the grain size distribution by analysis of scanning electron microscopy images, and the electrical behavior by the impedance spectroscopy technique. Sintering with the application of AC electric fields to 3YSZ enhances its ionic conductivity. An explanation is proposed, based on the dissolution back to the bulk of chemical species, which are depleted at the grain boundaries, leading to an increase in the oxygen vacancy concentration. For the enhancement of the grain boundary conductivity, an explanation is given based on the diminution of the concentration of depleted chemical species, which migrate to the bulk. This migration leads to a decrease of the potential barrier of the space charge region, known to be responsible for blocking the oxide ions through the intergranular region. Moreover, the heterogeneity of the distribution of the grain sizes is ascribed to the skin effect, the tendency of the AC current density to be largest near the surface, decreasing towards the bulk.

Palavras-Chave: sintering; yttrium; yttrium oxides; zirconium oxides; impedance; spectroscopy; microstructure; grain size; ionic conductivity

CARVALHO, SABRINA G.M.; MUCCILLO, ELIANA N.S.; MUCCILLO, REGINALDO. Electrical behavior and microstructural features of electric field-assisted and conventionally sintered 3 mol % yttria-stabilized zirconia. Ceramics, v. 1, n. 1, p. 1-10, 2018. DOI: 10.3390/ceramics1010002. Disponível em: http://repositorio.ipen.br/handle/123456789/28936. Acesso em: $DATA.

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