Abstract:
The purpose of this study was to investigate suitable sealing materials that prevent gas leakage in solid oxide fuel stack. Ceramic adhesives such as cerabond 516, 571, 569, 575, 584, 586, 645N, 685, 835 and 3062 that have the coefficients of thermal expansion close to that of solid oxide fuel cells component, ceramic - glass composite seals (consisting of Pyrex glass, ceramic powder of YSZ electrolyte and sodium aluminate additive) and composite seal using ceramic - glass composites with ceramic fiber 650 were selected in this paper. This study was concentrated on bonding between ferritic stainless steel and YSZ pellet, chemical compatibility in both oxidizing and reducing atmospheres, apparent porosity, coefficient of thermal expansion, thermal cycles, and gas leakage at 800 °c using He gradient pressure at 2 psig and dead load at 25 psi. It was found that the selected ceramic adhesives were not suitable as sealing because they had high leakage rate ≈ 0.5 cm³ / min . cm corresponding to the high apparent porosity. The ceramic - glass composites had detrimental phase cristobalite after the first thermal cycle (12 hrs) contributed to crack in seal although the gas leakage rate was low ≈ 10⁻⁴ cm³ / min . cm after the third thermal cycle (36 hrs). A composite seal containing ceramic fiber seemed promising from the low gas leakage rate ≈ 10⁻⁴ cm³ / min . cm after the third thermal cycle without deteriorating the cell components.