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Degradation mechanisms of sealing glasses for SOFC

Topic

Dual atmosphere for characterisation of sealing glasses at temperatures up 1000°C with electrical loads up to 30 V

Dual atmosphere for characterisation of sealing glasses at temperatures up 1000°C with electrical loads up to 30 V

Schematic setup of air and fuel glas flow and the electrical connections of model sealings in a dual atmosphere furnace

Schematic setup of air and fuel glas flow and the electrical connections of model sealings in a dual atmosphere furnace

Specific resistance of a standard SOFC sealing glass in model sealing with Crofer22APU under varying electric load (0,7V and 30V)

Specific resistance of a standard SOFC sealing glass in model sealing with Crofer22APU under varying electric load (0,7V and 30V)

Components of ceramic high temperature fuel cells (SOFC) such as metallic interconnectors (Crofer22APU, ITM/LC, CFY) and ceramic electrolytes (ZrO2-based) are sealed by special solder glasses. The glasses have to seal the air and fuel gas containing component of a SOFC stack against each other, where additionally electrical potentials between 0,7V and 1,3V are applied across the sealing seam. At these high temperatures reactions and migration processes of ions between the glassy phase the joint materials and the environmental atmospheres occur, which in turn cause degradation processes in the sealed components. According to this the sealing glasses must fulfill high requirements, because the amorphous fraction of the partial crystalline microstructure of the sealing glass forms a highly viscous liquid what allows a high mobility of ions. Especially the interfacial regions in contact with metallic material can be the subject of unwanted reactions leading to a declined adhesion of the sealing glasses.

The degradation processes can be simulated in various experimental testing devices. A dual atmosphere furnace allows the characterization of sealing glasses in model sealings at temperatures up to 1000°C where inside the sample a reducing and outside the sample an oxidizing atmosphere prevails. Additionally electrical loads up to 30V can be applied to the samples and their electric resistance can be measured insitu during testing.