Novel Compressive Mica Seals with Metallic Interlayers for Solid Oxide Fuel Cell Applications

A novel hybrid compressive mica seal was developed that showed an exceptionally low leak rate of ～8.9 × 10^?4 sccm/cm (standard cubic centimeters per minute per unit leak length of seal) at 800°C and a compressive stress of 100 psi, about 740 times lower than that of the conventional compressive mica seals (6.6 × 10^?1 sccm/cm), at a pressure gradient of 2 psi. The hybrid compressive mica seals were composed of two compliant metallic layers and a mica layer. Three commercially available micas were tested in this study. All showed substantial improvements in reducing the leak rates by using the hybrid design. The best results were obtained using muscovite single-crystal mica and 125 μm silver layers. Using the paper form of muscovite and phlogopite mica, the leak rates were still far superior (～1 × 10^?1 sccm/cm) compared with mica without the compliant silver layer (about 6–9 sccm/cm). The microstructure of the mica was examined before and after the 800°C leak tests. These results are compared with results for hybrid seals using glass interlayers. In addition, an explanation for the substantial reduction of the leak rates is proposed, and the application of the hybrid compressive mica seals in planar SOFC stacks is briefly addressed.