Effect of Bi₂O₃ on Thermal Properties of Barium-Free Glass-Ceramic Sealants in the CaO-MgO-B₂O₃-Al₂O₃-SiO₂ System

Abstract

Barium-free glass-ceramic sealants for the planar solid oxide fuel cell (pSOFC) have attracted considerable attention to avoid the crystallization of the high coefficient of thermal expansion (CTE) BaCrO4; reaction product at the interface between barium-containing glass-ceramic sealants and Crofer22 APU interconnect, which decreases the long-term mechanical stability of the sealant. In this study, Barium-free glass-ceramic sealants in the CaO-MgO-B2O3-Al2O3-SiO2 system with varying amounts of Bi2O3 from 0 to 10 wt. % were prepared by conventional melting and their thermal properties were investigated. The glass transition temperature (Tg), dilatometric softening temperature, and coefficient of thermal expansion (CTE) were determined by a dilatometer. The Tg, onset of crystallization (Tx) and crystallization temperature (Tc) were obtained from DTA. Results of phase analysis by X–ray diffraction of glasses after thermal treatment at 900 oC for 2 h indicated that the major phase of all glasses was diopside (MgCaSi2O6) and minor phases were åkermanite (Ca2MgSi2O7) and forsterite (Mg2SiO4). The Tg of the fabricated glasses tended to decrease with increasing Bi2O3 content while the CTE of glasses increased after the thermal treatment and was in the range of requirement for SOFC sealant.