Bonded compliant seals

In bonded compliant seals, a thin stamped foil is bonded to both sealing surfaces as shown in Fig. 5.10. A number of high-temperature alloys can be potential candidates for the foil membrane if they satisfy the following criteria. 

10 Foil-based bonded compliant seal (Weil 2006) 

Durafoil (22-Cr/7-Al/0.1-La + Ce/Fe) is a commercially used bonded foil as it satisfies the above-mentioned properties. The bonded compliant seals are non-sliding and metal foils endow a higher degree of geometric deformation. Under modest thermomechanical loading, the foil is deformed and may return to its original shape when the load is removed. 

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The various options for sealing and joining the ceramic and metal components in pSOFCs can be broadly classified into one of three categories rigid bonded seals, compressive seals, and bonded compliant seals. As outiined in Table 11.2, rigid... 

Bonded compliant seals Sealant bonds to adjacent pSOFC components and plastically deforms at room temperature and above... 

Weil, K.S. and Koeppel, B.J. (2008) Thermal stress analysis of the planar SOFC bonded compliant seal design. Int.J. Hydrogen Energy, 33, 3976-3990. 

Jiang, T.L. and Chen, M.H. (2009) Thermal-stress analyses of an operating planar solid oxide fuel cell with the bonded compliant seal design. Int. J. Hydrogen Energy, 34, 8223-8234. 

The joint region in compliant seals can be plastically deformed above room temperatures, which lessens the thermal stresses caused due to CTE mismatch. This category of sealants includes metallic components and hence is electrically conducting. In addition to this, the cell bowing and non-uniformities in the gas distribution are potential problems. Brazing and bonded compliant seals fall in this category and are discussed in Sects. 5.3.2.1 and 5.3.2.2. 

In the same year, Weil et al. [13] introduced a sealing concept for planar SOFCs. The finite element method (FEM) was used to aid in scaling up a bonded compliant sealant design to a 120 x 120 mm component. The stresses of the cell, foil, brazes, and frame were calculated and compared with experimental fracture and yield stress results. A quarter symmetrical model was used. The commercial software AN SYS was utilized. The tensile stress of the component was predicted, considering thermal cycling from elevated temperature to room temperature. The materials used were mentioned, but no properties were given. Regarding the structural analysis boundary conditions and the failure criteria employed, material models were not depicted. 

Bonded seals can be rigid or compliant. A hermetic seal is achieved through adhesive forces between the seal material and both surfaces against which the seal is to work. Naturally, the seal material must have good adhesive properties (good wettability of the material to be sealed). 

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