RAFAEL MORGADO BATISTA

RAFAEL MORGADO BATISTA

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Phase transformation/stabilization and ionic conductivity in tantalum oxide co‑doped zirconia‑scandia solid electrolyte
2022 - SOUZA, J.P.; FUJIMOTO, T.G.; BATISTA, R.M.; STEIL, M.C.; MUCCILLO, R.; MUCCILLO, E.N.S.
The influence of small amounts of tantalum oxide as co-dopant on phase transformation and stabilization, microstructure and ionic conductivity of zirconia-10 mol% scandia is reported in this work. Cylindrical pellets were prepared by solid state synthesis with sintering at 1500 °C for 5 h. High relative density values (> 95%) were achieved. Reduction of the enthalpy for the cubic ⇌β-rhombohedral phase transformation was found for increasing amounts of the co-dopant. Full stabilization of the cubic structure at room temperature was obtained with only 0.45 mol% tantalum oxide addition. The ionic conductivity of sintered specimens was investigated as a function of the temperature and oxygen partial pressure by impedance spectroscopy. The fully stabilized co-doped system revealed a pure ionic conduction behavior up to 800 °C with wide electrolytic domain. In the 700–800 °C range, the ionic conductivity of co-doped specimens is similar to that of pure zirconia-scandia.
Analysis of the sintering process in gadolinia-doped ceria by thermodilatometry and correlation with microstructure evolution
2018 - BATISTA, RAFAEL M.; MUCCILLO, E.N.S.
The non-isothermal sintering process of cerium dioxide containing gadolinium sesquioxide powders within a wide range of specific surface area was investigated by dilatometry. Linear shrinkage data of powder compacts were recorded under several constant rates of heating. Dilatometry data were analyzed by two methodologies enabling to preview the relative density for any temperature/time profile, and determination of the apparent activation energy for sintering. Correlation of dilatometry results with microstructure evolution was also carried out. Remarkable differences in sintering powders with different specific surface areas were found. The apparent activation energy for sintering increases with decreasing specific surface area and, in most cases, it does not change significantly in the approximately 70-85% range of relative density.
Dilatometry analysis of the sintering process of nanostructured gadolinia-doped ceria
2016 - BATISTA, R.M.; MUCCILLO, E.N.S.
The sintering process of compacts of nanostructured gadolinia-doped ceria was investigated by dilatometry and by construction of the master sintering curve. Corrections for the thermal expansion of the experimental setup and mass loss were proposed. The aim of this work was to investigate the sintering evolution of compacts constituted by a powder material with very high specific surface area and to verify the effectiveness of the proposed corrections for generating reliable density data. Validation of the obtained results was accomplished by comparison of corrected data with density values obtained for conventionally sintered compacts. Dilatometry experiments were carried out for 3, 6, 10 and 12 C min-1 heating rates. Good convergence of relative density curves calculated from corrected shrinkage data was obtained. The determined value of the activation energy for sintering of nanostructured gadolinia- doped ceria compacts is 576 kJ mol-1.
Sintering and electrical conductivity of gadolinia-doped ceria
2016 - BATISTA, R.M.; FERREIRA, A.M.D.C.; MUCCILLO, E.N.S.
Bulk specimens of Ce0.9Gd0.1O2-delta prepared with powders within a range of specific surface area were sintered in oxidizing, inert, and reducing atmospheres. The aim of this work is to investigate the effects of the sintering atmosphere on the microstructure and grain and grain boundary conductivities of the solid electrolyte. The lattice parameter determined by Rietveld refinement is 0.5420(1) nm, and the microstrain was found negligible in the powder materials. Specimens sintered in the Ar/4 % H-2 mixture display larger average grain sizes independent on the particle size of the starting powders. The grain and grain boundary conductivities of specimens sintered under reducing atmosphere are remarkably lower than those sintered under oxidizing and inert atmospheres. The activation energy (similar to 0.90 eV) for total electrical conductivity remains unchanged with both the initial particle size and the sintering atmosphere.
Densification and grain growth of 8YSZ containing NiO
2011 - BATISTA, R.M.; MUCCILLO, E.N.S.
Structure, microstructure and electrical conductivity of 8YSZ containing NiO
2011 - BATISTA, R.M.; MUCCILLO, E.N.S.