SHIRLEY LEITE DOS REIS

SHIRLEY LEITE DOS REIS

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Electrical behavior of electric field-assisted pressureless sintered ceria-20 mol% samaria
2019 - REIS, SHIRLEY L.; CARVALHO, SABRINA G.M.; MUCCILLO, ELIANA N.S.; MUCCILLO, REGINALDO
CeO2:20 mol% Sm2O3 green ceramic pellets were sintered conventionally at 1500 C/2 h and flash sintered by applying a 200 V cm􀀀1 electric field at 800 C, 1000 C and 1200 C. The thickness shrinkage of the pellets was followed bythe specimen being positioned inside a dilatometer adapted with platinum electrodes and terminal leads connected to a power supply for application of the electric voltage. The microstructure of the surfaces of the sintered samples were observed in a scanning electron microscope. The electrical properties were evaluated by the impedance spectroscopy technique in the 5 Hz–13 MHz frequency range from 210 C to 280 C. The main results show that (i) the final shrinkage level is nearly independent of the temperature when the electric field is applied and slightly better than that of the 1500 C sintered pellet, and (ii) the bulk conductivity of the sample flash sintered at 1200 C is similar to that of the sample sintered at 1500 C. The availability of a pathway for the electric current pulse derived from the applied electric field is proposed as the reason for the achieved shrinkages. Scavenging of the grain boundaries by Joule heating is proposed as the reason for the improved oxide ion bulk conductivity.
Sintering evaluation of doped lanthanum gallate based on thermodilatometry
2019 - BATISTA, R.M.; REIS, S.L.; MUCCILLO, R.; MUCCILLO, E.N.S.
The sintering behavior of La0.9Sr0.1Ga0.8Mg0.2O3-δ oxide-ion conductor was systematically investigated by thermodilatometry. The shrinkage data obtained with heating rates of 4, 7, 10 and 12 °C min−1 were analyzed by the constant rate of heating model and by construction of the master sintering curve. Validation of the master sintering curve was carried out by measurements of density in conventionally sintered specimens. Slight anisotropy of shrinkage data was found and changes to the basic equation of density was proposed to account for this effect. Plotting the data determined by the constant rate of heating model versus density allowed an easy identification of the density range of constant activation energy. The activation energy (865 kJ mol−1) obtained from the master sintering curve correlates quite well with that (874 kJ mol−1) obtained by the constant rate of heating model.
Influence of small amounts of gallium oxide addition on ionic conductivity of La0.9Sr0.1Ga0.8Mg0.2O3-δ solid electrolyte
2018 - REIS, S.L.; MUCCILLO, E.N.S.
The effects of small amounts of gallium oxide on intragrain and intergrain conductivity of La0.9Sr0.1Ga0.8Mg0.2O3-δ are investigated by impedance spectroscopy in the 280–420 °C range. Bulk specimens with 0.5, 1.0 and 1.5 mol% gallium oxide are prepared by solid state reaction at 1350 °C. All specimens achieved relative density values higher than 95%. The additive promotes grain growth indicating solid solution formation. A small fraction of the additive remains at grain boundaries and increases the fraction of the gallium-rich, LaSrGa3O7, impurity phase. The intragrain conductivity of gallium oxide containing specimens is higher than that of the parent solid electrolyte. Similar effect is found for the intergrain conductivity, which is maximum for 1 mol% gallium oxide addition.
Influence of additives on phase stabilization of scandia-doped zirconia
2017 - MUCCILLO, ELIANA N. dos S.; GROSSO, ROBSON L.; REIS, SHIRLEY L. dos; MUCCILLO, REGINALDO
The effects of small additions of tin, zinc, calcium and boron oxides on phase composition and electrical conductivity of zirconia-10 mol% scandia were investigated. Compounds containing 1 mol% zinc, tin and calcium oxides and 1, 3 and 5 wt.% boron oxide were prepared by solid state reaction and characterized by X-ray diffraction, density measurements, scanning electron microscopy and impedance spectroscopy. Full stabilization of the cubic structure at room temperature was obtained with additions of 1 mol% calcium oxide and 2 wt.% boron oxide. Partially stabilized compounds exhibit herringbone structure, characteristic of the β- rhombohedric phase. Specimens with calcium as additive show total conductivity of 23.8 mS.cm-1 at 750ºC with activation energy of 1.13 eV. Liquid phase sintering by boron oxide addition is effective to enhance the densification of the solid electrolyte.
Ionic conductivity and microstructure of fast fired Sr- and Mg-doped lanthanum gallate
2014 - REIS, SHIRLEY L.; MUCCILLO, ELIANA N. dos S.
La0.95Sr0.1Ga0.8Mg0.2O3-d ceramic prepared by two-step sintering
2015 - REIS, SHIRLEY L. dos; MUCCILLO, ELIANA N. dos S.
Microstructure and electrical conductivity of fast fired Sr- and Mg-doped lanthanum gallate
2016 - REIS, S.L.; MUCCILLO, E.N.S.
La0.9Sr0.1Ga0.8Mg0.2O3−δ solid electrolytes were consolidated by fast firing aiming to investigate the effects of the sintering method on densification, microstructure and ionic conductivity. Powder mixtures were prepared by solid state reaction at 1250 and 1350 °C for 12 h, and fast fired at 1450 and 1500 °C temperatures for 5 and 10 min. The content of impurity phases was found to be quite low with this sintering method. Relatively high density (>90% of the theoretical value) and low porosity (<1.5%) were readily obtained for powder mixtures calcined at 1250 °C. The activation energy for conduction was approximately 1 eV. Specimens fast fired at 1450 °C for 10 min with a mean grain size of 2.26 µm reached the highest value of total ionic conductivity, 22 mS cm−1, at 600 °C.
Phase composition, densification and electrical conductivity of Lasub(0.9)Srsub(0.1)Gasub(0.8)Mgsub(0.2)Osub(3-'delta') consolidated by the two-stage sintering method
2015 - REIS, S.L.; MUCCILLO, E.N.S.
The influence of the method of sintering on densification, phase assemblage and electrical conductivity of Sr- and Mg-doped lanthanum gallate was investigated aiming to optimize the sintering process of this solid electrolyte. Powder mixtures were prepared by solid state reactions, and the sintering of green compacts was carried out by the two-stage method varying the temperature of the first stage (T1) and the isothermal temperature (T2) and time (t2) profile. The type and content of predominant impurity phases depend on specific parameters of the sintering process. In the first stage of sintering, the content of impurity phases, such as LaSrGaO4 and La4Ga2O9, decreases with increasing temperature. The relative density of sintered specimens reaches 99% whenever T1 is 1500 1C. The mean grain size varies from 1.45 to 4.9 mm. At 600 1C the electrical conductivity attains 12 mS cm 1 for T1 1400 1C and T2 1350 1C for 5 h, with activation energy of approximately 1 eV.
Two-step sintering of samaria-doped ceria
2009 - REIS, S.L.; MUCCILLO, E.N.S.
Two-step sintering of samaria-doped ceria
2010 - REIS, S.L.; MUCCILLO, E.N.S.