T °C - JuSER - Forschungszentrum Jülich

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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.

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