Phase thermal stability and low thermal stress in MgO-BaO-CaO-Al2O3-B2O3-SiO2 glass-ceramic for long-term solid oxide fuel cells

The crystallization thermal stability plays an essential role in affecting thermal stress of glass-ceramic sealant for long-term planar-type solid oxide fuel cells (SOFC) to prevent fuel leakage during operation. Due to the lack of systematic research on regulating the stable performance of glass-based sealant with the working time at operation temperature, herein, the effect of MgO on crystallization kinetics, phase stability, and thermal and mechanical properties of MgO-BaO-CaO-Al2O3-B2O3-SiO2 (MBCABS) glass-ceramic has been firstly analyzed at heat-treatment of 750 degrees C with working time of 1 similar to 1000h in this work. Subsequently, the relationship evolution of crystallization thermal stability-coefficient of thermal expansion (CTE) match-thermal stress was established by Finite Element Method (FEM). The main reasons for the decrease of CTE of MBCABS glass-ceramics with low content MgO are the precipitation of hexagonal BaAl2Si2O8 phase and the transformation of hexagonal BaAl2Si2O8 to low-CTE monoclinic BaAl2Si2O8 phase, bring about that the Von Mises thermal stress of sealant itself and interface having tripled at 1000h (more than 200 MPa) according to FEM simulation results. The thermal stable and high-CTE BaMgSiO4, Ba8Mg16Si16O56, and BaCa2Mg(SiO4)(2) phases crystallized in MBCABS glass-ceramics with high-content MgO, therefore the maximum stress at all time parameters was below 100 MPa for 1 similar to 1000h. This study was useful for identifying the optimal phase option and CTE matching of glass-based sealant for efficient and stable long-term operation of solid oxide fuel cells.