Mechanical properties of tape cast nickel-based anode materials for solid oxide fuel cells before and after reduction in hydrogen
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The processing of solid oxide fuel cells (SOFCs) often involves co-sintering of multi-layered stacks. In the case of SOFCs incorporating Ni-based anodes, hydrogen reduction of the anode usually takes place during the first service cycle of operation or conditioning. Initial reduction causes changes in the chemistry, microstructure and properties of the Ni-based anode material, which in turn induce mechanical stresses in the cell. In this study the elastic moduli, biaxial strength and fracture toughness of unreduced (NiO-YSZ) and reduced (Ni-YSZ) anode were determined as functions of porosity. Elastic properties were determined by impulse excitation at ambient temperature. Biaxial strength and fracture toughness were determined at ambient temperature by the ring-on-ring and double torsion test methods, respectively. It was found that the mechanical properties of unreduced and reduced Ni-based anode materials depend strongly on porosity. Property-porosity trends were found to be in good agreement with prediction of the minimum solid area model. Results presented in this study show that the elastic moduli and biaxial strength of the Ni-based anode material decreases after reduction in hydrogen while fracture toughness increases after reduction due to formation of ductile Ni-metal phase. Published by Elsevier Ltd on behalf of Acta Materialia Inc.