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Channeled Ni-YSZ and Co-YSZ Anodes produced from Directionally Solidified Eutectics:

Channeled Ni-YSZ and Co-YSZ Anodes produced from Directionally Solidified Eutectics: Microstructural 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.

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Channeled Ni-YSZ and Co-YSZ Anodes produced from Directionally Solidified Eutectics:

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  1. Channeled Ni-YSZ and Co-YSZ Anodes produced from Directionally Solidified Eutectics: Microstructural 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@unizar.es

  2. 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

  3. Directionally Solidified Eutectics DSE self-organized lamellar microstructure & Strong 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

  4. DIRECTIONAL SOLIDIFICATION 20 mm Directional Solidification of Eutectics Lamellar melt grown composite Conventional NiO-YSZ ceramic • Minimization of the interfacial energy • Diffusion at the solid-liquid interface

  5. 2√2p √x SV = l 31/4l • Minimization of the interfacial energy: • self-organized lamellar microstructure if vol% minority phase x> 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.

  6. Laser-Assisted directional solidification NiO-YSZ Plate laser beam heater Ceramic substrate

  7. wp vp after the NiO Ni reduction Molten zone vc wc Samples for microstructural stability experiments produced byThe Laser Floating Zone technique Ø = 1.5 mm l = 10 cm Rods • Microstructural characterization • Electronic conductivity • Hg porosimetry rod axis

  8. red. H2 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

  9. Zr - YSZ Ni [110] [100] [100] [010] [110] [001] [001] 2 Å d = 2.94% 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

  10. (111) Ni // (002)YSZ 4 types of Ni-YSZ interfaces (002) Ni // (002)YSZ [110]YSZ – [110]NiO [110]YSZ – [100]NiO [100]YSZ – [110]NiO [100]YSZ – [100]NiO Polycrystalline Ni film deposited on a (100) cubic-ZrO2 substrate by MBE

  11. AGEING?: Microstructure Treatment in 4%H2-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

  12. AGEING?: Electrical conductivity rCermet rMetal 100 mA Measurements: RT - 4 point DC - RESISTIVITY ( in mWcm) rCermet Ni Co rMetal 112±11 37 0 hours CERMET 16 6 39 110±11 300 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.

  13. 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 hours300 hours % open % theoret. % relative 14.8 23.4 63.2 16.0 23.4 68.5 (open/theoret) Diameter (µm)

  14. 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.

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

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