The Development of Thermally Stable Sealing Glass in the BaO–B2O3–SiO2 System for Planar SOFC Applications

Abstract

The purpose of the present paper is to study the influence of glass composition on the thermal stability in the SiO2–B2O3–BaO system, and three glasses were consequently investigated. Although Glass A has a coefficient of thermal expansion (CTE) that shows the best match with those of anode and electrolyte materials of solid oxide fuel cells (SOFCs), the thermal stability of Glass A is quite poor, where after being heat treated at 800°C for only 8h, the CTE of the glass increased more than 24%. The change of the CTE value was mainly attributed to the fast crystallization that formed high CTE value phases such as BaB2O4 and Ba2Si3O8. In order to improve the thermal stability, BaO in Glass A was replaced by B2O3 (Glass B) and SiO2 (Glass C). It was found that the decrease in the BaO content improved the thermal stability of the resultant glasses. Glass B showed less than 8% change of the CTE during annealing time at 800°C, while Glass C exhibited superior long-term thermal stability, where the change of the CTE was within the equipment detection limit after being heat treated for 300h at 800°C. The good thermal stability of Glass C was believed to be due to the formation of a more compact glass network after the substitution as compared with that of Glass A. The good thermal stability makes Glass C attractive to be used as the sealing material for SOFC applications.