In this study, we report that effects of a filler with a high coefficient of thermal expansion on a sealant for high-temperature (750 ~850 o C) SOFC. We designed a SiO 2 -BaO-ZnO-B 2 O 3 -Al 2 O 3 glass system with a softening temperature higher than 750 o C. The properties of the glass system show not only low volumetric shrinking but also low swelling. The glass system did not create a crystal phase during along-term heat treatment. We fabricated a seal gasket with 0, 10, 15, and 20 wt% cristobalite added as filler materials with glass powder. The coefficient of thermal expansion of the seal gasket increased according to cristobalite content. During alongterm heat treatment, the leak rate decreased by about 5% after a heat treatment in an oxidizing atmosphere at 750 o C for 2000 h, also decreasing by about 6% after a heat treatment in a reducing atmosphere at 750 o C for 1000 h.
The influences of Na and K content on the crystal phase, the microstructure and the electrical property of BaTiO 3 -based thermistors was found to show typical PTC effects. The crystal phase of powder calcined at 1000 o C for 4hrs showed a single phase with BaTiO 3 , and the crystal structure was transformed from tetragonal to cubic phase according to added amounts of Na and K. In XRD results at 43 (002), (020) and (200) peaks. In sintered bodies, those calcined at 600 o C rather than at 1000 o C were dense, and for certain amounts of Na and K showed rapid decreases in grain size. In relative permittivity, the curie temperature due to the transformation of ferroelectric phase rose with added Na and K but decreased in terms of relative permittivity. In the result of the R-T curve, the sintered bodies have curie temperatures of about 140 o C and the resistivity of sintered bodies have scores of Ω·cm; the jump order of sintered bodies was shown to be more than 10 4 in powder calcined at 1000 o C.Key words PTC, Pb-free, heater, BaTiO 3 , Na and K.
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