A designed compositional series of 22 devitrifiable glasses for sealing solid oxide fuel cell components was studied. Candidate oxides were selected on the basis of chemical compatibility with the fuel cell environment. The influence of each component on viscosity, thermal expansion, and crystallization were evaluated through systematic addition to a base composition. The most promising results were achieved within the system
BaO–SrO–normalB2normalO3–Al2normalO3–Ta2normalO5–SiO2
. Additions of
SrO
and
BaO
maximize the thermal expansion of the bulk glass, achieving a coefficient of thermal expansion ranging from 10.8 to
13.9ppm∕K
(200–500°C)
. Devitrification of the glasses yielded similar thermal expansion coefficients ranging from 10.7 to
14.4ppm∕K
. The addition of
Al2normalO3
and
Ta2normalO5
allows a critical sealing viscosity to be achieved at
900°C
in a glass with just
6mol%
of
normalB2normalO3
. Five promising candidate sealing glasses have been identified.
In experimental whiteware coatings comprised of zircon pigment and multi-oxide silicate glass frits that incorporated ZrO 2 , the quantity, size, and morphology of zircon that precipitated during "fast-firing" were mainly dependent upon the ZnO, SrO, and Al 2 O 3 :alkali levels. In these frits, little or no zircon pigment dissolution occurred, and zircon crystallization was nearly complete by 1000°C. Microstructures of the coatings were consistent over a range of peak firing temperatures from 1000°to 1100°C. Fritted ZnO in these coatings stimulated zircon crystallization and produced high opacity. Replacing ZnO with SrO in the same frits prevented zircon from precipitating and resulted in transparent coatings. In frits without ZrO 2 , significant zircon pigment dissolution and crystallization of calcium-based silicates occurred during firing. In these unstable coatings, crystallization and dissolution increased from 1000°to 1100°C and produced a range of microstructures. Raising the Al 2 O 3 :alkali ratio caused frits with ZrO 2 to precipitate more zircon, and frits without ZrO 2 to form less of the calcium-based silicates and dissolve less pigment.
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