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Lecture

Electric field assisted sintering of polycrystal ceria inside a transmission electron microscope

Wednesday (26.09.2018)
15:30 - 15:45 S1/03 - 283
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Ceramic materials play an important role in science, technology and industry, they provide a variety of applications in our modern life. The manufacturing of ceramics is always an energy-intensive and time-consuming activity, thereby researchers has been working on the optimizing of the sintering technique for decades. The electric field shows the potential to reduce the energy requirement, form specific microstructures or even modify the conductivity of grain boundaries.1 2 3 In this contribution, we aim to observe the dynamic evolution of pre-sintered ceramics and ceramic powders under the influence of external DC/AC electric field. A special focus will put on the neck formation, grain growth, pore shrinking and variation in component at grain boundary areas.


10% yttrium doped cerium dioxide (YDC10) powders was calcined to improve their sintering performance. The non-uniform particles have an average size of about 14 nm. Pre-sintered YDC10 green body with a density of ~ 60% was made in to transmission electron microscopy specimen with a thickness of less than 200 nm using focused ion beam (FIB) technique. Heating and electrical biasing experiment was performed in a FEI Titan 80-300 scanning transmission electron microscope (STEM) equipped with a monochromator and a spherical aberration corrector for the probe forming system. The lamellar specimen was heated up from 500 oC to 1200 oC with an interval of 100 oC and a heating rate of 10 oC/ min. The temperature was held for 30 min for isothermal experiments in order to determine the transition point of each sintering stages. High-angle annular dark-field (HAADF) images were acquired over both the entire specimen area and at regions where particles agglomerate. It turns out that the particles start to combine with each other at a temperature of 700oC. This process becomes faster as the temperature reaches 900oC. Afterwards, shrinkage of the entire specimen starts to be visible. From 1100 oC a rapid shrinkage is evident.


On-going in-situ experiment will put a focus on the influence of electric field on the surface diffusion. Both DC and AC electric field will be applied as electric loading at a temperature raging from 700 oC to 900 oC. Simultaneous electron energy loss spectroscopy (EELS) mapping at grain boundaries will be utilized to identify the segregation of yttrium during the sintering process.

Speaker:
Zheng Ma
Forschungszentrum Jülich GmbH
Additional Authors:
  • Dr. Lei Jin
    Forschungszentrum Jülich GmbH
  • Dr. Vadim Migunov
    Forschungszentrum Jülich GmbH
  • Chen Cao
    Forschungszentrum Jülich GmbH
  • Dr. Robert Mücke
    Forschungszentrum Jülich GmbH
  • Prof. Dr. Rafal Dunin-Borkowski
    Forschungszentrum Jülich GmbH
  • Prof. Dr. Olivier Guillon
    Forschungszentrum Jülich GmbH