Alumina–silica glass–ceramic sealants for tubular solid oxide fuel cells

In this work, we synthesized the glasses of the SiO2–Al2O3–CaO–Na2O–MgO–K2O–B2O3–Y2O3 system and investigated their thermal properties under changes in the ratios between the components in both modifying (MgO/CaO) and glass-forming (SiO2/B2O3) oxides. In addition, the effects of crystallization on both the properties of sealants and their behaviour at the boundary with ceramic yttria-stabilized zirconia (YSZ) electrolyte have been studied. X-ray diffraction analysis was used to determine the phase composition of the glasses both after quenching, dilatometric measurements and sealing of the glasses with the YSZ ceramic support. The thermal expansion coefficients (CTEs) found for the glasses and glass–ceramics are shown to be in good agreement with those of other cell components. The sealing temperatures of these materials are found to be lower than the operating temperature limit of the interconnector alloy. It is shown that Mg-rich glasses exhibit higher resistance to interaction with Cr compared to other compositions under study. The scanning electron microscopy and energy dispersive spectroscopy studies have confirmed the formation of gas-tight connections by the sealants under investigation. The glass demonstrating the highest stability in contact with the Crofer22APU alloy has been tested as a sealant for a tubular cell. This material is established to ensure a tight connection without cracks during operation at 850 °C for 250 h. The materials are thus found to be promising candidates for use as sealants for solid oxide fuel cells (SOFCs).