A barium-free glass-ceramic SOFC sealant composition. Part B: In-situ crystallization study by high-temperature microscopy

Optimized barium-free, of composition 56.9SiO 2 –5.1CaO–9.0Al 2 O 3 –9.2B 2 O 3 –12.6SrO–2.7K 2 O–2.5Na 2 O–2.0ZrO 2 (SCABS), viscous sealants were successfully tested against SOFC electrolytes and interconnect materials for up to 960 h. This glass exhibit glass transition temperature near 678°C, a Littleton temperature close to 845°C, which corresponds to a viscosity of 10 7.6 dPa.s, and a thermal expansion coefficient of 8.0 × 10 -6 °C -1 . Direct observation of surface crystallization by HT-ESEM for 144 h at 850°C shows that multiphase assemblies of crystals are formed, and their growth velocity is of the order of 17 µm/day. When this glass is brought into contact with a K41 alloy for 960 h at 850°C, the interface area affected is of the order of 2 to 3 µm on the glass side. This area consists mainly of a continuous layer of chromium oxide. In addition, 60 to 65% of the glass volume is crystallized. This potentially confers good mechanical properties on the seal at high temperatures and may make it possible to adapt the seal to the stresses applied to the fuel cell.