The effect of CaO/MgO content on properties of barium aluminosilicate sealants for solid oxide fuel cells

Abstract

Design of an appropriate sealant is crucial for reliable sealing and stable long-term operation of solid oxide fuel cells. We have investigated sealants based on barium aluminosilicate glass-ceramic modified with CaO and MgO. Focus of the research was on the 0.33BaO-0.20XO-0.33SiO2–0.05Al2O3–0.09B2O3 system, where XO is CaO, MgO, or a mixture of the two. Key properties of the system were studied, and its applicability of different compositions to sealing of high-temperature solid oxide fuel cells was investigated. Thermal properties, such as softening point and a half-ball point of the glass, coefficients of thermal expansion and adhesion to Crofer 22APU steel were of primary concern. CaO-containing sealants of this system showed much lower softening point compared to that of MgO-containing sealants. The substitution of CaO with MgO had no detectable effect on the coefficients of thermal expansion of the sealants. The coefficients of all the studied compositions were in 11.2–11.6∙10−6 1/K range. All the compositions have good adhesion to both Crofer 22 APU steel and ZrO2-based electrolyte. CaO-containing sealant was tested under operation conditions of a fuel cell stack for ten days; the seal remained hermetic for that period with no visible signs of degradation or oncoming failure of the seal.