Thermal cycling stability of novel hexagonal boron nitride (h-BN)/glass compressive seals for planar intermediate temperature solid oxide fuel cells.

The novel h-BN/glass compressive seals were investigated for use in solid oxide fuel cell. The glass was mixed with h-BN powders to obtain composite materials using tape casting technique. Leakage rates were measured below 0.012 sccm/cm under input gas pressure of 6.8 kPa. Seals containing 40% by weight glass showed excellent thermal cycle and long-term operation stability. The leakage rates were reduced by more than half after ten thermal cycles under different input gas pressure. Also, the leakage rates gradually decreased to 0.008 sccm/cm under input gas pressure of 20.4 kPa at 750 °C during 208 h, and then remained stable. These observations can be explained by liquid B 2 O 3 films having gradually formed on the h-BN surface. Boron oxidation effectively improved bondage for both interface and interior particles. This phenomenon was interpreted by seals' microstructure analyses and transmission electron microscopy. Finally, an evolution model is proposed to explain the process. • h-BN/glass compressive seals exhibit excellent thermal cycling stability. • The leakage rate decreases to stable 0.008 sccm/cm after 208 h at 750 °C. • A core-shell structure model is proposed to explain reduced low leakage rate. [ABSTRACT FROM AUTHOR]