Energy and Nuclear Research Institute CCTM

Brazil

Energy and Nuclear Research Institute CCTM

Brazil
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Batista R.M.,Energy and Nuclear Research Institute CCTM | Muccillo E.N.S.,Energy and Nuclear Research Institute CCTM
ECS Transactions | Year: 2011

The effect of small amounts of nickel oxide on the microstructure and the electrical conductivity of zirconia-8 mol% yttria was systematically investigated by scanning electron microscopy and impedance spectroscopy techniques. Nickel carbonate was added to commercial yttria-stabilized zirconia powder, and the mixture was used to prepare green compacts. Sintering experiments were carried out at several sintering temperatures. The electrical conductivity of sintered specimens are similar for nickel oxide additions up to 1 mol% and sintering times up to 5 h. For larger sintering times, reduction of the grain boundary electrical conductivity, along with microstructure defects were observed in specimens containing the additive. Energy-dispersive spectroscopy analysis in several micro-regions of sintered specimens revealed a heterogeneous distribution of nickel. The nickel segregation phenomenon occurring with long sintering times is responsible for an additional blocking effect on the electrical conductivity of the solid electrolyte. ©The Electrochemical Society.


Batista R.M.,Energy and Nuclear Research Institute CCTM | Muccillo E.N.S.,Energy and Nuclear Research Institute CCTM
Ceramics International | Year: 2011

The effects of NiO addition on sintering yttria-stabilized zirconia were systematically studied to understand the role of the additive in the sintering process of the solid electrolyte. Specimens of 8 mol% yttria-stabilized zirconia with NiO contents up to 5.0 mol% were prepared using different Ni precursors and sintered at several dwell temperatures and holding times. Densification and microstructural features were studied by apparent density measurements and scanning electron microscopy observations, respectively. The sintering dynamic study was carried out by following the linear shrinkage of powder compacts containing 0-0.75 mol% NiO. Small (up to 1.0 mol%) NiO addition was found to improve the sinterability of yttria-stabilized zirconia. The activation energy for volume diffusion decreases with increasing NiO content, whereas the grain boundary diffusion seems to be independent on this additive. The grain growth of yttria-stabilized zirconia is found to be enhanced even for small NiO contents. © 2010 Elsevier Ltd and Techna Group S.r.l.


Batista R.M.,Energy and Nuclear Research Institute CCTM | Muccillo E.N.S.,Energy and Nuclear Research Institute CCTM
Ceramics International | Year: 2011

The effects of NiO addition on the structure and microstructure of yttria-stabilized zirconia were investigated to clarify the role of the additive in the microstructure-related electrical conductivity of the solid electrolyte. Specimens of 8 mol% yttria-stabilized zirconia with NiO contents up to 5.0 mol% were prepared using nickel oxide and trihydroxi nickel carbonate as precursors. The specimens were sintered at 1350 °C for several holding times. The evolution of the lattice parameter with NiO content was evaluated by X-ray diffraction and the microstructural features by scanning electron microscopy. Electrical conductivity was evaluated by impedance spectroscopy measurements. The solubility limit of NiO at 1350 °C was found to be 1.5 mol% by X-ray diffraction. Energy dispersive spectroscopy results revealed Ni segregation for large holding times at 1350 °C. The grain boundary conductivity was found to be influenced by Ni segregation and to decrease with increasing holding times at high temperature. © 2011 Elsevier Ltd and Techna Group S.r.l.


Souza E.C.C.,Energy and Nuclear Research Institute CCTM
Journal of Electroceramics | Year: 2013

The electrochemical behavior of a symmetrical cell, Pt/Ce 0.8Sm0.2O1.9-δ/Pt, under reducing conditions and wide temperature range (250 - 600 C) is detailed. In terms of the charge carriers transport through the electrolyte microstructure, AC impedance spectroscopy has been applied to address useful concerns about the transport properties over electrolytic and mixed conduction regimes. The impedance spectra at lower temperature and oxygen partial pressure show the electrochemical response of separated bulk and grain boundary contributions. The increase in the electronic conductivity from 250 to 400 C shows that the electrochemical reduction Ce4+/Ce3+ is as kinetic as thermodynamically favorable in the experimental conditions. In a typical Nyquist plot of an impedance diagram, until temperatures as low as 400 C, the high and low frequency arcs can be accessed and the influence of reducing atmosphere over both the components is presented. The apparent activation energy for the electronic process (ΔE) extracted from the total conductivity is 2.54 eV. Distinguished bulk (2.34 eV) and grain boundary (2.63 eV) activation energies point the latter as an energetic barrier in the redox reaction. The oxygen partial pressure dependence of individual capacitances suggests storage of electrical charge along grain boundaries which can potentially behave as a chemical capacitor. © 2013 Springer Science+Business Media New York.

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