Cobalt containing crystallizing glass seals for solid oxide fuel cells - A new strategy for strong adherence to metals and high thermal expansion

Powdered glasses based on the systems BaO/CoO/SiO2 and BaO/ZnO/CoO/SiO2 with small additions of ZrO2, La2O3 and B2O3 were investigated with respect to their sintering and crystallization behavior. They could be fully densified by viscous flow and during subsequent crystallization BaSi2O5 and Ba(ZnxCo2−x)Si2O7 or BaCo2Si2O7 were formed. The CTEs (100-800 °C) of crystallized samples were 14.0-14.6 × 10−6 K−1. Sealing experiments with Nicrofer© alloy showed strong adherence of the crystallized glass. Aluminum from the alloy is oxidized and forms an alumina layer or interconnected structures inside the metal. Cobalt oxide as a component of the glass is reduced to the metal and occurs as approximately spherical particles near the Nicrofer© alloy. The number of cobalt particles increases with increasing sealing temperature. During fracture of sealed Nicrofer© plates, the crack runs through the glass and not through the interface metal/crystallized glass.