Efeito da Gália como aditivo de sinterização em eletrólitos cerâmicos à base de céria sintetizados pelo método de complexação de cátions
Fuel cells are considered one of the most promising ways of converting electrical energy due to its high yield and by using hydrogen (as fuel) which is considered one of the most important source of clean energy for the future. Rare earths doped ceria has been widely investigated as an altern...
Sábháilte in:
| Príomhchruthaitheoir: | |
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| Rannpháirtithe: | |
| Formáid: | doctoralThesis |
| Teanga: | por |
| Foilsithe / Cruthaithe: |
Universidade Federal do Rio Grande do Norte
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| Ábhair: | |
| Rochtain ar líne: | https://repositorio.ufrn.br/jspui/handle/123456789/12851 |
| Clibeanna: |
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| Achoimre: | Fuel cells are considered one of the most promising ways of converting electrical
energy due to its high yield and by using hydrogen (as fuel) which is considered one of
the most important source of clean energy for the future. Rare earths doped ceria has
been widely investigated as an alternative material for the electrolyte of solid oxide fuel
cells (SOFCs) due to its high ionic conductivity at low operating temperatures compared
with the traditional electrolytes based on stabilized zirconia. This work investigates the
effect of gallium oxide (Gallia) as a sintering aid in Eu doped ceria ceramic electrolytes
since this effect has already been investigated for Gd, Sm and Y doped ceria
electrolytes. The desired goal with the use of a sintering aid is to reduce the sintering
temperature aiming to produce dense ceramics. In this study we investigated the effects
on densification, microstructure and ionic conduction caused by different molar fraction
of the dopants europium (10, 15 and 20%) and gallium oxide (0.3, 0.6 and 0.9%) in
samples sintered at 1300, 1350 and 1450
0
C. Samaria (10 and 20%) doped ceria samples
sintered between 1350 and 1450 °C were used as reference. Samples were synthesized
using the cation complexation method. The ceramics powders were characterized by
XRF, XRD and SEM, while the sintered samples were investigated by its relative
density, SEM and impedance spectroscopy. It was showed that gallia contents up to
0.6% act as excellent sintering aids in Eu doped ceria. Above this aid content, gallia
addition does not promote significant increase in density of the ceramics. In Ga free
samples the larger densification were accomplished with Eu 15% molar, effect
expressed in the microstructure with higher grain growth although reduced and
surrounded by many open pores. Relative densities greater than 95 % were obtained by
sintering between 1300 and 1350 °C against the usual range 1500 - 1600
0
C. Samples
containing 10% of Sm and 0.9% of Ga reached 96% of theoretical density by sintering
at 1350
0
C for 3h, a gain compared to 97% achieved with 20% of Sm and 1% of Ga co-doped cerias sintered at 1450
0
C for 24 h as described in the literature. It is found that
the addition of gallia in the Eu doped ceria has a positive effect on the grain
conductivity and a negative one in the grain boundary conductivity resulting in a small
decrease in the total conductivity which will not compromise its application as sintering
aids in ceria based electrolytes. Typical total conductivity values at 600 and 700 °C,
around 10 and 30 mS.cm
-1
respectively were reached in this study. Samples with 15% of
Eu and 0.9 % of Ga sintered at 1300 and 1350 °C showed relative densities greater than
96% and total conductivity (measured at 700 °C) between 20 and 33 mS.cm
-1
. The
simultaneous sintering of the electrolyte with the anode is one of the goals of research in
materials for SOFCs. The results obtained in this study suggest that dense Eu and Ga
co-doped ceria electrolytes with good ionic conductivity can be sintered simultaneously
with the anode at temperatures below 1350 °C, the usual temperature for firing porous
anode materials |
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