High Temperature Glass-ceramic Seals for SOFC Applications

A novel borosilicate glass, gc9, with the main compositions of BaO-Al2O3-B2O3-SiO2 and other minor additives, has been developed by INER as a high temperature seal for solid oxide fuel cell (SOFC) stacks. The glass transition temperature (T-g) and softening temperature (T-s) of gc9 glass are 652 degrees C and 745 degrees C, respectively. Its average coefficient of thermal expansion (CTE) is about 11.0 ppm/degrees C (RT similar to 800 degrees C), which is compatible with that of interconnect and MEA of a SOFC stack. Additionally, a proper balance of sealant properties, such as its viscosity and shrinkage behavior at different temperatures, is essential to have a successful sealing for a SOFC stack. The viscosity evolution and shrinkage amount of a gc9 glass powder pellet at elevated temperatures were measured using a high temperature parallel plate viscometer. Under an external loading of 0.080 MPa, the minimum viscosity, viscosity reflection point, and shrinkage percentage are 10(8) Pa.s, 806 degrees C, and 64%, respectively.