Thermal cycle stability of a novel glass–mica composite seal for solid oxide fuel cells: Effect of glass volume fraction and stresses

A novel glass–mica composite seal was developed based on a previously reported concept of “infiltrated” mica seals for solid oxide fuel cells. Ba–Al–Ca silicate sealing glass powder and Phlogopite mica flakes were mixed at glass volume fractions of 10–50 vol.% to make the glass–mica composite seals. The seals were leak tested for short-term thermal cycle stability as a function of glass volume fraction. Composite seals with 10 and 20 vol.% glass were also leak tested under compressive stresses from 3 to 100 psi and helium pressures of 0.2 or 2 psi. Post-mortem microstructure analyses were used to characterize the fracture (leak path) of the glass–mica composite seals and were related to the high temperature leakages. Open circuit voltage tests on dense 8YSZ electrolyte with the glass–mica composite seal showed very good thermal cycle stability over 250 cycles with minute (<1%) voltage drop.