Bilayered Glass-Ceramics as Sealants for SOFCs

Glass-ceramics are often used as sealants in solid oxide fuel cells (SOFC). But interfacing components, such as ferriticstainless steel and YSZ electrolyte, may vary in their requirements regarding sealing properties, especially in terms of thermalexpansion. 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 goodbonding characteristics to the ferritic steel and the other to the YSZ electrolyte. Steel and electrolyte components were coated with alayer of their corresponding glass sealant paste and heated up to form a sandwich sample. During the heat treatment of the sealingprocess, 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 sealantsby mechanical testing. The designed bilayered glass-ceramics fulfill the special requirements of ferritic steel and YSZ. They showexcellent potential to become a new outstanding sealant for SOFCs.