High temperature gas seals
View Patent ↗A flexible seal for use in a solid oxide fuel cell stack is formed from a fiber matrix with a plurality of solid particles through tape casting method. The fibers and particles are preferably ceramic and may be formed from alumina or zirconia. The seal may be formed by forming a slurry of fibers, particles, a binder and a non-aqueous solvent, tape casting the slurry, drying the tape seal, die-cutting, prior to installation in the fuel cell stack.
1. A solid oxide fuel cell stack comprising a plurality of adjoining fuel cells, wherein the fuel cells are mutually sealed in a gas-tight manner by a seal formed of:
ceramic fibres providing a matrix for retaining ceramic powder, and being capable of remaining flexible at operating temperatures of the fuel cell;
ceramic powder being disposed within the matrix, a substantial proportion of the ceramic powder having a particle size of about 5 μm in diameter;
the ceramic fibres and powder being capable of resisting sintering at operating temperatures of the fuel cell, wherein the seal is substantially free of binder and has a fired porosity between about 35% to about 60%.
2. The solid oxide fuel cell stack of claim 1 wherein the ceramic fibres and ceramic powder may be the same material or different and may comprise alumina or zirconia.
3. The solid oxide fuel cell stack of claim 2 wherein the seal has a pre-fired porosity of less than about 45%.
4. The solid oxide fuel cell stack of claim 3 wherein the seal has a pre-fired porosity of less than about 40%.
5. The solid oxide fuel cell stack of claim 4 wherein the seal has a pre-fired porosity of about 35%.
6. The solid oxide fuel cell stack of claim 1 or claims 2 to 5 which is formed by a tape casting process.
7. The solid oxide fuel cell stack of claim 6 which has a fired porosity of less than about 50% and greater than about 35%.
8. The solid oxide fuel cell stack of claim 7 which has a fired porosity of less than about 45% and greater than about 35%.
9. The solid oxide fuel cell stack of claim 8 which has a fired porosity of less than about 40% and greater than about 35%.
10. A composition for forming a gas seal against adjoining fuel cells in a solid oxide fuel cell stack comprising:
ceramic fibres providing a matrix for retaining ceramic powder, and being capable of remaining flexible at operating temperatures of the fuel cell, and in an amount between about 5% to about 40% by weight;
ceramic powder being disposed within the matrix, a substantial proportion of the ceramic powder having a particle size of about 5 μm in diameter; and in an amount between about 50% to about 90% by weight;
the ceramic fibres and powder being capable of resisting sintering at operating temperatures of the fuel cell, wherein the seal is substantially free of binder and has a fired porosity between about 35% to about 60%;
a plasticizer in an amount between about 1% to about 15% by weight;
an organic binder in an amount between about 2% to about 5% by weight;
a dispersant in an amount greater than about 1% by weight; and
a solvent.