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

摘要

Powdered glasses based on the systems BaO/CoO/SiO_2 and BaO/ZnO/CoO/SiO_2 with small additions of ZrO_2, La_2O_3 and B_2O_3 were investigated with respect to their sintering and crystallization behavior. They could be fully densified by viscous flow and during subsequent crystallization BaSi_2O_5 and Ba(Zn_xCo_(2-x))Si_2O_7 or BaCo_2Si_2O_7 were formed. The CTEs (100-800 ℃) 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.