Tuning the thermal properties of borosilicate glass ceramic seals for solid oxide fuel cells

In this paper, a series of Sr–Ba–borosilicate glass-ceramics (10–40 mole% B2O3) were prepared to investigate the effect of borate content on the thermal properties as well as volatilization behavior. For crystallized samples with increasing borate contents, the dilatometric softening points decrease, from 702 to 660 °C, as do the coefficients of thermal expansion, from 9.5 to 7.5 × 10−6 K−1. In addition, the weight loss from these materials, in wet forming gas at 780 °C for 28 days, decreases by a factor of two as the borate content increases from 10 to 40 mole%. The borate-containing phase, SrB2O4, forms with increasing borate content. The significant improvement in stability against volatility can be attributed to the formation of SrB2O4, which is consistent with the results of thermochemical calculations. These results therefore indicate one way to design sealing compositions to use B2O3 to tailor thermal properties without sacrificing thermal stability.