Degradation of Sealing Glasses for SOFC under Electrical Load and Dual Atmosphere
A. Rost, J. Schilm, M. Kusnezoff, A. Michaelis
Fraunhofer Institute for Ceramic Technologies and Systems, Winterbergstrasse 28, 01277 Dresden, Germany
received January 12, 2012, received in revised form March 2, 2012, accepted March 22, 2012
Vol.3, No.2, Pages 69-80 DOI: 10.4416/JCST2012-00002
For reliable operation of planar solid oxide fuel cells (SOFC), long-term stability of the sealing materials, including gas tightness and bonding to the joined materials, is essential. Failures induced by thermal cycling, slight stack deformation or degradation of the sealing material can lead to leakages and undesired combustion of fuel gas, causing hot spots and severe damage of stacks or whole systems. Suitable partially crystallizing SOFC sealing glasses are presented and characterized in terms of their softening properties, viscosity, thermal expansion and crystallization behaviour. However, it is not sufficient to characterize these internal properties. For reliable long-term operation, structural changes of sealing glasses and particularly reactions between interconnector materials and sealing glasses have to be considered. Therefore model sealings are tested in dual atmospheres with applied voltage. The resistivities of these arrangements were monitored continuously and changes in the microstructure of the joints were investigated after testing. The results are discussed in terms of the devolution of resistivity of model sealings at high temperatures and the microstructures of the sealing glasses and the glass-to-metal interfaces. After the identification of critical glass components, the development of enhanced sealing glasses with improved degradation properties is demonstrated and shown for one composition.
Crystallization, degradation, sanbornite, sealing glasses, SOFC
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