Electrical conductivity of Y-doped CGO based materials sintered by hot press

Commercial ceria?gadolinia powders were used to prepare dense CGO (5 mol% Gd) samples, by hot press method at relatively low temperature (1000?C). To study the effect of post-sintering, further the as-sintered bodies were subjected into different thermal treatments 1100oC-1400oC. The sintered samples were characterized by impedance spectroscopy as a function of temperature in air, in order to identify each microstructural contribution to the overall electrical behaviour. Scanning electron microscopy shows that the increase in the temperature of thermal treatment leads to grain growth. Electrical properties were studied with different oxygen partial pressuresand ion blocking methods. Y2O3 (5 wt%) additions were used to seek the grain boundaries heterogeneities effectsin CGO material, prepared by hot press and subjected into post sintering thermal treatments. Electrical conductivities of CGO samples were analysed with and without Y2O3 additions.6D12-6554-B318 | Jo?o Carlos Castro Abrantesinfo:eu-repo/semantics/acceptedVersio

Optimization of low-grade tetragonal zirconia by praseodymium oxide additions

Zirconia-based materials are still the state of art electrolyte for high temperature electrochemical systems, and for non-electrochemical applications. Their purity is known to affect performance, thus requiring high-grade expensive precursors and additional concerns about contamination during high temperature processing and/or during long term applications at intermediate temperatures, as found for contamination by silica. Thus, the purpose of this work was to demonstrate the scavenging ability of praseodymium oxide to minimize or suppress the impact of contamination by silica. In the present work, one used TZP precursor powders from Tosoh and Innovnano. Starting materials of both powders contained significant fractions of monoclinic phase, coexisting with tetragonal zirconia, and yielded highly dense samples after sintering at 1450?C/2h. Praseodymium oxide and/or silicon oxide additions did not affect significantly the sintering behaviour. Additions of Pr and Si yielded co-existing tetragonal and cubic phases, as revealed by XRD and Rietveld refinements, with an impact on lattice parameters of the cubic phase. The electrical characterization showed the expected severe decrease in conductivity after the addition of silicon oxide addition and also showed that this negative impact is at least partially reverted by additions of praseodymium oxide.6D12-6554-B318 | Jo?o Carlos Castro Abrantesinfo:eu-repo/semantics/publishedVersio

Optimization of low-grade CGO transport properties for SOFC applications

Grain boundaries are frequently responsible for a poor performance of gadolinium-doped ceria-based electrolytes, due to a low ionic conductivity, orders of magnitude smaller than the bulk conductivity. Silica, the dominant impurity in many low-grade ceramics, namely, in ceria-based materials, has a detrimental effect on grain boundaries conductivity. Several previous works had explored the silica-scavenging effect. In the present work, we exploit an alternative approach using the addition of 5% (w/w) of Y2O3, as silica scavenging agent, and sintering by hot pressing at low temperature to minimize bulk dissolution of yttrium in the CGO lattice. Gadolinium-doped ceria-based powders were co-fired with additions of 1% (w/w) of silica, and silica and yttrium oxide to test the silica scavenging role of yttrium. The samples were prepared by hot press at low temperature (1000?C) and were characterized by impedance spectroscopy as a function of temperature in air, in order to de-convolute different microstructural contributions to the overall electrical behaviour. Combined information obtained from structural, microstructural, and electrical characterization allowed one to study the impact of new phases on the resulting ceria-based solid electrolytes.6D12-6554-B318 | Jo?o Carlos Castro Abrantesinfo:eu-repo/semantics/publishedVersio

Study of oxygen-ion conductivity and luminescence in the ZrO2-Nd2O3 system : impact of local heterogeneity

Stabilized fluorites and pyrochlores with different types of substitution in the (Nd2O3 ? ZrO2 system (NdZrO)) have been studied by Raman spectroscopy, X-ray diffraction, and impedance spectroscopy methods. Ionic and proton conductivity maps for 9 compositions in the NdZrO system are presented. Oxygen partial pressure measurements show a typical ionic conductor behavior, with a significantly increase of conductivity for (Nd2?xZrx)Zr2O7+x/2 (x = 1.27) fluorite and (Nd2?xZrx)Zr2O7+x/2 (x = 0.4, 0.2) pyrochlores. For the same compositions the strong luminescence was observed. Strong luminescence and high oxygenion conductivity of these solid solutions can be associated with the presence of phases with the different degree of structural disorder (tetragonal phase, fluorite) in local nanodomains in fluorite or pyrochlore matrix in the ZrO2 ? Nd2Zr2O7 region. Really, Raman spectra of (Nd2?xZrx)Zr2O7+x/2 (x = 0.5 ? 0.2) solid solutions demonstrated the fluorite + pyrochlore structural type in the short-range order. Fluorite nanodomains in pyrochlore matrix (ZrO2 ? Nd2Zr2O7 region) resulting from an order?disorder transition can only be detected at a radiation wavelength comparable to the fluorite nanodomain size. Thus, using Raman spectroscopy the broad isomorphism range in the ZrO2 ? Nd2Zr2O7 system has been shown to be nonuniform.371C-9F16-EBDE | Eduarda GomesN/

Effect of Pr3+/Pr4+ ratio on the oxygen ion transport and thermomechanical properties of the pyrochlore and fluorite phases in the ZrO2-Pr2O3 system

This paper examines the effect of the Pr3+/Pr4+ ratio on the mechanism of ionic and electronic transport in the (Pr2?xZrx)Zr2O7+x/2 (x = 0.15), Pr2Zr2O7, and Pr2(Zr2?xPrx)O7?x/2 (x = 0.1) pyrochlore phases and Pr3ZrOx with the fluorite structure and on the behavior of their thermal expansion coefficient (TEC). The solid solutions were prepared through coprecipitation followed by firing of the green compacts in air at a high temperature of 1550 ?C for 4 h. The Pr3+/Pr4+ ratio was shown to decrease in going from the (Pr2?xZrx)Zr2O7+x/2 (x = 0.15), Pr2Zr2O7, and Pr2(Zr2?xPrx)O7?x/2 (x = 0.1) pyrochlores to the Pr3ZrOx fluorite, leading to changes in the conductivity type from mixed (ionic?electronic) to electronic and in the color of the materials from beige to black and to an anomalous deviation of the TEC from linearity in fluorite Pr3ZrOx, i.e. at the highest Pr4+ content. According to impedance spectroscopy results, (Pr2?xZrx)Zr2O7+x/2 with x = 0.15 has purely oxide-ion conductivity (3 ? 10?3 S/cm at 1000 ?C) in a wide range of oxygen partial pressures: from 10?10 to 102 Pa. With increasing Pr content, p-type electronic conductivity becomes significant, reaching a maximum in fluorite Pr3ZrOx: ?0.5 S/cm at 1000 ?C. According to XPS data, all pyrochlore samples (Pr2?xZrx)Zr2O7+x/2 (x = 0.15), Pr2Zr2O7 and Pr2(Zr2?xPrx)O7?x/2 (x = 0.1) contain only Pr3+ at room temperature, whereas Pr3ZrOx contains both Pr3+ and Pr4+. The considerable deviation of the TEC of Pr3ZrOx from linearity above 500 ?C is due to partial reduction of Pr4+. The reduction process Pr4+ + e? ? Pr3+ followed by oxygen release in the range 500?1100 ?C has been identified in Pr3ZrOx by thermal analysis and mass spectrometry in a He atmosphere.371C-9F16-EBDE | Eduarda GomesN/

Evolution of oxygen-ion and proton conductivity in Ca-Doped Ln2Zr2O7 (Ln = Sm, Gd), located near pyrochlore fluorite phase boundary

Sm2-xCaxZr2O7-x/2 (x = 0, 0.05, 0.1) and Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1) mixed oxides in a pyrochlore-fluorite morphotropic phase region were prepared via the mechanical activation of oxide mixtures, followed by annealing at 1600 ?C. The structure of the solid solutions was studied by X-ray diffraction and refined by the Rietveld method, water content was determined by thermogravimetry (TG), their bulk and grain-boundary conductivity was determined by impedance spectroscopy in dry and wet air (100-900 ?C), and their total conductivity was measured as a function of oxygen partial pressure in the temperature range: 700-950 ?C. The Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) pyrochlore solid solutions, lying near the morphotropic phase boundary, have proton conductivity contribution both in the grain bulk and on grain boundaries below 600 ?C, and pure oxygen-ion conductivity above 700 ?C. The 500 ?C proton conductivity contribution of Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) is ~ 1 ? 10-4 S/cm. The fluorite-like Gd2-xCaxZr2O7-x/2 (x = 0.1) solid solution has oxygen-ion bulk conductivity in entire temperature range studied, whereas proton transport contributes to its grain-boundary conductivity below 700 ?C. As a result, of the morphotropic phase transition from pyrochlore Sm2-xCaxZr2O7-x/2 (x = 0.05, 0.1) to fluorite-like Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1), the bulk proton conductivity disappears and oxygen-ion conductivity decreases. The loss of bulk proton conductivity of Gd2-xCaxZr2O7-x/2 (x = 0.05, 0.1) can be associated with the fluorite structure formation. It is important to note that the degree of Ca substitution in such solid solutions (Ln2-xCax)Zr2O7-? (Ln = Sm, Gd) is low, x < 0.1. In both series, grain-boundary conductivity usually exceeds bulk conductivity. The high grain-boundary proton conductivity of Ln2-xCaxZr2O7-x/2 (Ln = Sm, Gd; x = 0.1) is attributable to the formation of an intergranular CaZrO3-based cubic perovskite phase doped with Sm or Gd in Zr sublattice. ? 2019 by the authors.371C-9F16-EBDE | Eduarda GomesN/

Heterogeneities in leishmania infantum infection : using skin parasite burdens to identify highly infectious dogs

Background: The relationships between heterogeneities in host infection and infectiousness (transmission to arthropod vectors) can provide important insights for disease management. Here, we quantify heterogeneities in Leishmania infantum parasite numbers in reservoir and non-reservoir host populations, and relate this to their infectiousness during natural infection. Tissue parasite number was evaluated as a potential surrogate marker of host transmission potential. Methods: Parasite numbers were measured by qPCR in bone marrow and ear skin biopsies of 82 dogs and 34 crab-eating foxes collected during a longitudinal study in Amazon Brazil, for which previous data was available on infectiousness (by xenodiagnosis) and severity of infection. Results: Parasite numbers were highly aggregated both between samples and between individuals. In dogs, total parasite abundance and relative numbers in ear skin compared to bone marrow increased with the duration and severity of infection. Infectiousness to the sandfly vector was associated with high parasite numbers; parasite number in skin was the best predictor of being infectious. Crab-eating foxes, which typically present asymptomatic infection and are non-infectious, had parasite numbers comparable to those of non-infectious dogs. Conclusions: Skin parasite number provides an indirect marker of infectiousness, and could allow targeted control particularly of highly infectious dogs

Cognitive effects of the progressive exercise test in electricians wearing personal protective equipment.

Objetivo: verificar o efeito do esfor?o f?sico sobre as fun??es cognitivas de trabalhadores eletricistas utilizando equipamento de prote??o individual (EPI). M?todos: participaram 28 eletricistas que trabalhavam na constru??o, manuten??o e opera??o de redes de distribui??o de energia. Todos do sexo masculino, sadios e aptos para a pr?tica de exerc?cios f?sicos. As fun??es cognitivas foram representadas pelo teste de rea??o simples (TRS) e pelo n?vel de vigil?ncia mental (NVM). O TRS e o NVM foram mensurados pr? e p?s- -teste m?ximo progressivo, em esteira rolante, a 27 ?C de temperatura seca e umidade relativa do ar de 64%. O teste consistiu em aumentos progressivos na velocidade e na inclina??o da esteira at? a fadiga, com utiliza??o de EPI. Resultados: a m?dia (desvio padr?o) do TRS n?o foi significativamente diferente antes, 227,8 (35,1) ms, e ap?s o exerc?cio, 220,6 (24,6) ms. O NVM foi significativamente maior ap?s o exerc?cio em todas as situa??es: frequ?ncia crescente ? 36,5 (5,1) Hz vs 39,5 (2,7) Hz, frequ?ncia decrescente ? 36,0 (5,2) vs 39,0 (3,88) Hz, e frequ?ncia geral ? 36,2 (4,9) vs 39,2 (3,1) Hz. Conclus?o: o exerc?cio progressivo m?ximo realizado com EPI n?o modificou o tempo de rea??o simples e aumentou o n?vel de vigil?ncia mental de eletricistas.Objective: to verify the effects of physical effort on the cognitive functions of electricians wearing personal protective equipment (PPE). Methods: 28 electricians participated. They worked on the construction, maintenance and operation of electrical power distribution networks. All were male, healthy and able to practice physical exercises. The cognitive functions were checked by measuring simple reaction time (SRT) and mental alertness level (MAL). SRT and MAL were measured before and after progressive maximal exercise, on a treadmill, at 27 ?C dry temperature and 64% relative humidity, wearing PPE. The test consisted of progressive increases in treadmill speed and incline, until fatigue. Results: SRT mean difference was not significantly different before ? 227.8 (35.1) ms ? and after exercising ?220.6 (24.6) ms. MAL was significantly higher after exercise in all situations: increasing frequency - 36.5 (5.1) Hz vs. 39.5 (2.7) Hz; decreasing frequency-36.0 (5.2) Hz vs. 39.0 (3.88) Hz; and general frequency 36.2 (4.9) Hz vs. 39.2 (3.1) Hz. Conclusion: progressive maximal exercise performed while wearing PPE caused no change in simple reaction time, and increased electricians? mental alertness level

Histomorphometric analysis of inflammatory response and necrosis in re-implanted central incisor of rats treated with low-level laser therapy

Low-level laser therapy is a tool employed in the management of post-operative inflammation process and in the enhancement of reparative process. The aim of the study was to perform histological evaluation of dental and periodontal ligament of rats central upper-left incisor teeth re-implanted and irradiated with low-level laser (InGaAl, 685 nm, 50 J/cm2) 15, 30, and 60 days after re-implantation. Seventy-two male rats had the central upper left incisor removed and kept for 15 min on dry gauze before replantation. Laser was irradiated over the root surface and empty alveolus prior replantation and over surrounding mucosa after the re-implantation. After histological procedures, all slices were analyzed regarding external resorption area and histological aspects. We observed an increase of root resorption (p < 0.05) in the control group compared to the laser group at 15, 30, and 60 days. These results showed that the laser groups developed less root resorption areas than the control group in all experimental periods. Additionally, histological analysis revealed less inflammatory cells and necrotic areas in laser groups