Sin ttulo de diapositiva

1
Channeled Ni-YSZ and Co-YSZ Anodes produced from
Directionally Solidified Eutectics Microstructura
l Stability M. A. Laguna-Bercero, A. Larrea,
R. I. Merino, J. I. Peña and V. M.
Orera Instituto de Ciencia de Materiales de
Aragón, C.S.I.C. U. Zaragoza c/ María de Luna
3, E-50.018 Spain
Presenting author alarrea_at_unizar.es
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Outline

• Introduction
• Material preparation
• Directional solidification of eutectics
• Cermet properties
• Composition Microstructure
• Ni-YSZ interfaces
• Stability of the cermet microstructure
• Ageing experiments
• - Summary

• SEM TEM
• Electrical conductivity
• Hg porosimetry

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Directionally Solidified Eutectics
DSE self-organized lamellar microstructure Stro
ng interphase bonding
YSZ electrolyte deposited by MOCVD on a Ni-YSZ
channeled cermet
Channeled Ni-YSZ cermet
YSZ
Ni
pore
Fracture of a Ni-YSZ channeled cermet
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Directional Solidification of Eutectics
Lamellar melt grown composite
Conventional NiO-YSZ ceramic

• Minimization of the interfacial energy
• Diffusion at the solid-liquid interface

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• Minimization of the interfacial energy
• self-organized lamellar microstructure if vol
  minority phase xgt 28
• NiO-YSZ (x 0.43)
• CoO-YSZ (x 0.39)
• low energy interfaces (strong bonding)

SV 2/l
l

• Diffusion at the solid-liquid interface
• lamellar thickness controlled by the growth rate
• l2 R 117 mm2 mm/h (NiO-CaSZ)1
• l2 R 116 mm2 mm/h (CoO-YSZ)2

L
b
a
l
1 R.I. Merino et al. Recent Res. Devel. Mat. Sci.
4 (2003) 1-24. 2 J-i Echigoya and S. Hayashi, J.
Crystal Growth 129 (1993) 699-705.
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Laser-Assisted directional solidification
NiO-YSZ Plate
laser beam
heater
Ceramic substrate
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Samples for microstructural stability experiments
produced by The Laser Floating Zone technique
Ø 1.5 mm l 10 cm
Rods

• Microstructural characterization
• Electronic conductivity
• Hg porosimetry

rod axis
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Microstructure YSZ channels porous metal
channels
Ni-YSZ 45.6 YSZ 54.4 porous-Ni
41 vol pore 59 vol metal
75 NiO 25 8YSZ (mol)
(CTE a 10.8 x 10-6 K-1)
43 vol pore 57 vol metal
Co-YSZ 40.7 YSZ 59.3 porous Co
80 CoO 20 8YSZ (mol)
(CTE a 10.7 x 10-6 K-1)
YSZ
pore
Co
Ni-YSZ, fracture
Co-YSZ, polished cross section
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Matching (002) Ni // (002)YSZ
Christensen Carter, J. Chem. Phys. 114 (2001)
5816.
J. I. Beltrán et al., Phys. Rev B 68 (2003)
075401.
Works of separation from ab initio DFT
calculations WZr/N i 5014 mJ/m2 WO/Ni 5743
mJ/m2
sep
sep
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4 types of Ni-YSZ interfaces
(002) Ni // (002)YSZ
110YSZ 110NiO
110YSZ 100NiO
100YSZ 110NiO
100YSZ 100NiO
Polycrystalline Ni film deposited on a (100)
cubic-ZrO2 substrate by MBE
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AGEING? Microstructure
Treatment in 4H2-N2 at 900 ºC The lamellar
microstructure and the low energy interfaces
between metal and YSZ ensure a good
microstructural stability of the cermets SEM
TEM No microstructural evolution during the
treatment
Ni-YSZ 300 h
Ni-YSZ 0 h
Co-YSZ 300 h
Co-YSZ 0 h
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AGEING? Electrical conductivity
Measurements RT - 4 point DC -
RESISTIVITY (? in mWcm)
rCermet
Ni
Co
rMetal
11211
37
0 hours
CERMET
16
6
39
11011
300 hours
-
-
6.84
6.24
METAL Bulk
256
0 h
Ni-YSZ
-
-
37
286
1
300 h
833
0 h
-
Ni-YSZ
-
122
2
1041
300 h
1 Simwonis, D., Tietz, F. Stöver, D., Solid
State Ionics, 2000, 132, 241-251. 2
Skartmousos, D., Tsoga, A., Noumidis, A.
Nikolopoulos, P., Solid State Ionics, 2000, 135,
439-444.
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AGEING? Hg porosimetry
PORE SIZE DISTRIBUTION
Co-YSZ
Cermet porosity
0 hours 300 hourss
open theoret. relative
15.2 26.2 58.0
13.8 26.2 52.3
(open/theoret)
Ni-YSZ
0 hours 300 hours
open theoret. relative
14.8 23.4 63.2
16.0 23.4 68.5
(open/theoret)
Diameter (µm)
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Summary

• Channelled Ni-YSZ and Co-YSZ cermets for use in
  SOFC
• Alternating channels (400 nm wide) of YSZ and
  porous metal
• Strong Ni-YSZ interfacial bonding
• The lamellar microstructure and the strong
  bonding between the YSZ and the metal prevent the
  coarsening of the metal particles in working
  conditions
• After 300 h in 4 H2-N2 at 900 ºC
• No microstructural evolution in SEM TEM
  observations.
• No drop in electronic conductivity.
• No significant pore evolution.

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Acknowledgments

• Ministerio de Ciencia y Tecnología (Spain),
• Project MAT2003-1182.
• I3P Program, financed by the European Union.