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Bilayered Glass-Ceramics as Sealants for SOFCs



Author(s)

Stefanie Hauber^1,3, Svenja Dittrich^2,3, Tobias M. Walter², Bernhard Durschang¹, Karl G. Schell², Ethel C. Bucharsky², Elisabeth Reitz³,Gerhard Sextl¹ and Michael J. Hoffmann²

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DOI:10.17265/2161-6213/2019.3-4.001

1. Fraunhofer ISC, Würzburg 97082, Germany
2. Karlsruhe Institute of Technology IAM-KWT, Karlsruhe 76131, Germany
3. ElringKlinger AG, Dettingen an der Erms 72581, Germany

Glass-ceramics are often used as sealants in solid oxide fuel cells (SOFC). But interfacing components, such as ferritic stainless steel and YSZ electrolyte, may vary in their requirements regarding sealing properties, especially in terms of thermal expansion. A bilayered glass-ceramic system was developed to overcome the mismatch in coefficients of thermal expansion (CTE) between ferritic steel and YSZ. Therefore, two different glass-ceramics with slightly different CTEs were developed, one with good bonding characteristics to the ferritic steel and the other to the YSZ electrolyte. Steel and electrolyte components were coated with a layer of their corresponding glass sealant paste and heated up to form a sandwich sample. During the heat treatment of the sealing process, the glasses are crystallized into glass-ceramics. The resulting interface between the two glass-ceramics is of special interest. Cross-sections of the sandwich samples were cut, polished and investigated using SEM. The glass-ceramics show continuous, gap-free layers and excellent bonding to both steel and YSZ. Energy release rates are measured for single and bilayered glass sealants by mechanical testing. The designed bilayered glass-ceramics fulfill the special requirements of ferritic steel and YSZ. They show excellent potential to become a new outstanding sealant for SOFCs.

SOFC, bilayered glass-ceramic sealant, screen-printing, Charalambides, crystallization.