Effects of Al2O3 on (1−x)[SrO–SiO2–B2O3]–xAl2O3 glass sealant for intermediate temperature solid oxide fuel cell

The effects of Al2O3 on (1−x)[SrO–SiO2–B2O3]–xAl2O3 (SASB, x=0, 0.02, 0.04, 0.06, 0.08, and 0.1) sealing glasses for intermediate temperature solid oxide fuel cell (SOFC) have been investigated to determine the proper amount of Al2O3 for the application of the SASB glasses to a SOFC sealant. The structural, thermal, mechanical and adhesion properties were determined by using DTA, TMA, XRD, SEM, and Raman spectroscopy. It is found that the thermal expansion coefficients of the glasses and crystallized samples are 8.0–11.0×10−6 °C−1, and ~10.0×10−6 °C−1, respectively, which are within the required values for the SOFC sealant. The change of mode population in Raman scattering analysis shows that Al2O3 acts as a network modifier. When annealed at 800 °C, the glasses with x=0 and 0.1 start to crystallize in 5 h, but the sample with x=0.6 mostly remains as a glass phase even after 50 h, and this crystallization behavior has a close relationship with adhesion properties. Comparing the cross-sectional views of SEM images between x=0 and x=0.06, the sample with x=0.06 shows homogeneous morphologies with good adhesion and clean surface boundaries between the sample and substrate. But for the x=0 case, the boundaries are not clearly defined and devitrifications with heterogeneous morphologies exist.