New glass-ceramic sealants for SOFCs application: characterization and compatibility with interconnects

New barium-free glass-ceramic sealants were designed, characterised and tested in SOFC relevant conditions. Differential Thermal Analysis (DTA) and Hot Stage Microscopy (HSM) were used to investigate their sintering and crystallization behaviour. Thermal analyses have been carried out on glass powders with different particle sizes, at different heating rates, in order to evaluate the activation energy for the crystallization. The wetting and sealing behavior of the glass-ceramics on bare, pre-oxidised and Mn-Co based spinel-coated stainless steel has been examined. The joining process was optimised by considering the influence of glass particle size on the slurry paste formulation and on the sintering behaviour. Coated steel/glass-ceramic/uncoated steel joined samples were tested at 800°C up to 3500 hrs in air. Joined samples were also submitted to dual atmosphere tests (air and Ar/H2) with and without the effect of electrical potentials. SEM-EDS post-mortem analyses were carried out to understand the thermal behaviour and to investigate on degradation processes at the glass-ceramic/steel interface. The compatibility between the glass-ceramic sealants and the stainless steel (bare, pre-oxidised and coated) after tests in air and dual atmosphere is reviewed and discussed.