T °C - JuSER - Forschungszentrum Jülich

Summary 109
8. Summary
In the joining technology, composite materials based on glass, glass ceramics (GC)
and glass ceramic composites (GCC) become more and more important. Due to the
increasingly required multi-functionality of the sealant material (for e.g. coefficient of
expansion, flow ability, etc…), the developed sealant material used today is based on
glass ceramic composites. With these, a good adhesion of the joining components, a
good flow ability of the sealant material during the joining process and a good
electrical insulation and mechanical strength have to be achieved.
The joining process has to take place at temperatures < 900 °C. The operation
conditions of the SOFC are: 600 – 800 °C under oxidizing as well as reducing
atmospheric conditions. The present Thesis shows that, based on the use of
database and thermochemical methods, sealing materials can be swiftly adjusted to
all process and operation requirements.
In order to do this especially, with regards of the thermo-mechanical properties of the
developed sealant material (coefficient of expansion and flow ability) during the
joining process, a new concept has been designed. Joining tests have been achieved
on sandwich samples.
The starting point of this new concept is a metal/glass matrix composite where the
coefficient of expansion was controlled by dispersing a metal phase in the glass
matrix.
The newly developed concept is based on glass as a matrix and a crystalline phase
as a filler material. It is essential that the crystalline phase and the glass matrix
composition consist of the same thermodynamic co-existence area of the selected
oxide base system. Here, the glass matrix has a lower liquidus temperature
compared to the crystalline filler material, while the crystalline phase which consist of
a higher coefficient of expansion is used alone to tailor the coefficient of expansion of
the joining material. By incorporating a single crystalline phase into the selected
glass matrix, the coefficient of expansion of the sealant material matched the value of
the joined material component.
In this work and on this approach, it has been shown that by incorporating the
crystalline filler material barium silicatphase (BS) based on the system BaO-MgO-
SiO2 into the selected glass matrix consisting of the same co-existence area from the
selected oxide system, the coefficient of expansion would be tailored in the range of
9 to 15·10 -6 K -1 depending on the variation of the mass ratio of the BS-crystalline
phase.