Compression Properties and Leakage Tests of Mica‐Based Seals for SOFC Stacks

Abstract

Sealing properties and compression properties of two mica‐based materials, Thermiculite 866 and Statotherm HT were measured. Thermiculite 866 was tested in two forms: as‐made and precompressed (consolidated). Sealing tests were carried out at 800 °C with simulated fuel cell anode gas. Seals were pressed to a constant thickness, which represents the conditions in fuel cell stacks. Both seals showed stable leak rates over test periods of roughly 400 h. Leak rates of Thermiculite 866 samples were found to be independent of the hydrogen overpressure within the measurement accuracy in the pressure range of 10–100 mbar(g). However, a Statotherm HT gasket tested with lower compression stress compared to Thermiculite 866 gaskets showed roughly linear dependency on the overpressure. Compression tests were carried out at room temperature and at 800 °C. Compression properties of both materials were found to strongly depend on temperature. Both materials experienced swelling when heated to 800 °C and were more ductile compared to room temperature.

Room temperature and high temperature sealing properties and compression properties of compressive gaskets made of micrometric vermiculite particles

“…The same behaviour was found for Thermiculite® commercial gaskets (Rautanen et al, 2009) for which a 6 × 10 −2 atm·cm 3 ·s −1 ·m −1 leak rate was reported in the temperature range of 25-600°C at 5 bar He, under 20 MPa. Using the same unity, for our gaskets (circumference 40.8 mm) the leak rate value equal to 2.5 × 10 −2 atm·cm 3 ·s −1 ·m −1 is comparable to the one of Thermiculite® commercial gaskets.…”

“…They contain few talc particles and can resist up to 800°C (Hoyes, 2007). Upon 100 mbar of hydrogen and a compressive stress of 4-8 MPa, the leak rate was found to be close to 1-3 · 10 − 1 atm·cm 3 ·s − 1 (Rautanen et al, 2009). Upon 15 mbar of a mixture of N 2 -H 2 (50/50 vol.)…”

“…Moreover, vermiculite can withstand temperature heating up to 800°C, without any main change in its layered structure. Due to its ability to exfoliate (separation of the layers) by thermal shock or chemical reaction, and its thermal compatibility until 800°C, vermiculite has been extensively used as material for high temperature compressive gaskets in many applications (Hoyes et al, 1998;Fergus, 2005;Batfalsky et al, 2006;Dunn et al, 2006;Hoyes, 2007;Wiener et al, 2007;Rautanen et al, 2009).…”

Post-experimental analysis of a solid oxide fuel cell stack using hybrid seals

“…Compressible seals would have required much larger compression stress to flatten the cutting burrs. Additionally, the gap clearance variation would have likely been an issue due to the limited compressibility of Thermiculite 866 [5]. There are many reasons that can lead to a variation of gap clearance in a stack, i.e.…”

“…Compressible seals composed of mica-type paper have been investigated as an alternative [5e7]. The drawback of compressive seals is that in order to achieve acceptable leak rate, a compression stress of the order of several MPa has to be applied on the stack [5]. However, it was found that the leak rate remains significantly higher compared to glass ceramic seals and that the needed level of compression and the necessary compression system becomes technically challenging for large footprint stack.…”