Crystallization kinetics of a solid oxide fuel cell seal glass by differential thermal analysis

Abstract

Crystallization kinetics of a barium–calcium aluminosilicate glass (BCAS), a sealant material for planar solid oxide fuel cells (SOFC), have been investigated by differential thermal analysis (DTA). From variation of DTA peak maximum temperature with heating rate, the activation energy for glass crystallization was calculated to be 259 kJ/mol using a kinetic model. Development of crystalline phases on thermal treatments of the glass at various temperatures has been followed by powder X-ray diffraction. Microstructure and chemical composition of the crystalline phases were investigated by scanning electron microscopy and energy dispersive spectroscopic (EDS) analysis. BaSiO 3 and hexacelsian (BaAl 2Si 2O 8) were the primary crystalline phases whereas monoclinic celsian (BaAl 2Si 2O 8) and (Ba x Ca y )SiO 4 were also detected as minor phases. Needle-shaped BaSiO 3 crystals are formed first, followed by the formation of other phases at longer times of heat treatments. The glass does not fully crystallize even after long-term heat treatments at 750–900 °C. Devitrification of the glass seal over a long period of time during operation of the SOFC would generate thermal stresses in the seal and may have adverse effects on its mechanical performance. This may lead to cracking of the seal, resulting in mixing of the fuel and the oxidant gases.