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 Spain *Presenting author:

- Introduction - Material preparation Directional solidification of eutectics - Cermet properties Composition & Microstructure Ni-YSZ interfaces - Stability of the cermet microstructure Ageing experiments - Summary Outline SEM & TEM Electrical conductivity Hg porosimetry

Channeled Ni-YSZ cermet Directionally Solidified Eutectics DSE self-organized lamellar microstructure & Strong interphase bonding YSZ electrolyte deposited by MOCVD on a Ni-YSZ channeled cermet Fracture of a Ni-YSZ channeled cermet YSZ Ni pore

DIRECTIONAL SOLIDIFICATION Directional Solidification of Eutectics Conventional NiO-YSZ ceramic Lamellar melt grown composite  Minimization of the interfacial energy  Diffusion at the solid- liquid interface 20  m

 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)  Diffusion at the solid-liquid interface: lamellar thickness controlled by the growth rate  R = 117  m 2 mm/h (NiO-CaSZ) 1 2 R = 116  m 2 mm/h (CoO-YSZ) 2 S V = 2/ 2√2  S V = 3 1/4 √x 1 R.I. Merino et al. Recent Res. Devel. Mat. Sci. 4 (2003) J-i Echigoya and S. Hayashi, J. Crystal Growth 129 (1993)  L

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

Rods Samples for microstructural stability experiments produced by Samples for microstructural stability experiments produced by The Laser Floating Zone technique pp cc vcvc vpvp Molten zone Ø = 1.5 mm l = 10 cm after the NiO Ni reduction Microstructural characterization Electronic conductivity Hg porosimetry rod axis

(CTE:  = 10.8 x K -1 ) Microstructure: YSZ channels & porous metal channels red. H 2 Co-YSZ: 40.7 YSZ porous Co 75 NiO – 25 8YSZ (mol%) 80 CoO – 20 8YSZ (mol%) Ni-YSZ: 45.6 YSZ porous-Ni 43% vol pore 57% vol metal 41% vol pore 59% vol metal Ni-YSZ, fractureCo-YSZ, polished cross section (CTE:  = 10.7 x K -1 ) Co YSZ pore

Matching (002) Ni // (002)YSZ Christensen & Carter, J. Chem. Phys. 114 (2001) Works of separation from ab initio DFT calculations: W Zr/N i = 5014 mJ/m 2 W O/Ni = 5743 mJ/m 2 J. I. Beltrán et al., Phys. Rev B 68 (2003) Å [110] [001] [100] [110] Zr - YSZ  = 2.94% [100] [001] [010] Ni sep

(002) Ni // (002)YSZ 4 types of Ni-YSZ interfaces (111) Ni // (002)YSZ [110]YSZ – [110]NiO [100]YSZ – [110]NiO [110]YSZ – [100]NiO [100]YSZ – [100]NiO Polycrystalline Ni film deposited on a (100) cubic-ZrO 2 substrate by MBE

Ni-YSZ 0 h Co-YSZ 300 h Ni-YSZ 300 h Co-YSZ 0 h AGEING?: Microstructure Treatment in 4%H 2 -N 2 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

Measurements: RT - 4 point DC - [1] Simwonis, D., Tietz, F. & Stöver, D., Solid State Ionics, 2000, 132, [2] Skartmousos, D., Tsoga, A., Noumidis, A. & Nikolopoulos, P., Solid State Ionics, 2000, 135, Ni Co CERMET Ni-YSZ [1] [2] RESISTIVITY (  in  cm) 112± METAL Bulk  Cermet  Metal ± hours 300 hours 0 h 300 h h 1041 AGEING?: Electrical conductivity 100 mA  Cermet  Metal

0 hours 300 hourss 0 hours 300 hours PORE SIZE DISTRIBUTION (open/theoret) AGEING?: Hg porosimetry Co-YSZ Ni-YSZ % open % theoret. % relative % open % theoret. % relative Diameter (µm) Cermet porosity

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% H 2 -N 2 at 900 ºC  No microstructural evolution in SEM & TEM observations.  No drop in electronic conductivity.  No significant pore evolution. Summary

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