Thermal Cycle Stability Of SOFC Seal Material

One of the major challenges for the commercialization of SOFC is the development of suitable sealing materials. Since the tightness was achieved by different materials and methods, researchers began to focus on the long term stability and thermal cycle performance. Thermal cycle stability of Al₂O₃ based composite seal, developed in previous work, was evaluated.Prepared by tape casting, the Al₂O₃ based composite seals have shown low leakage at various compressive load and various inlet pressures in initial firing. It is obviously observed that the leakage of the seals declined with increasing aluminum content. Leakage rate was tested during thermal cycling to evaluate the thermal cycle stability of Al₂O₃ based composite seal. During thermal cycles, leakage rates of all samples, tested at a compressive load of 0.2MPa and a inlet pressures of 3.5kPa, increase slightly but stay below 0.04 sccmï¹'cm^-1 . Thermal stability enhanced with the Al content increase. The increment of leakage rate of ACS3 sample with 30wt% Al content after 92 thermal cycles was barley to detect.The effect of Al content on thermal cycling stability involved a spherical shell structure observed in the SEM microstructure of the fractured surfaces for the post-test samples. Leak paths, in interface result in the thermal stress due to the mismatch of CET of the seal and neighboring component has been affirmed by the SEM microstructure observing of interconnect/seal/cell sandwich structure samples. The leak path, including microcracks, oxidation of interconnect, led to the leakage rate increase during thermal cycling.Samples with best performance were inducted to single cell and stack thermal cycle test. The incrassation of Al₂O₃ based composite seal, degradating the stack contact, was measured and calculated.