Glass ceramics are supposed to produce stable sealants between ceramic electrolyte and ferritic steel in planar SOFC stacks. The screen printing method is a suitable industrial process in order to produce layers with tailored height and width reproduc-ibly. An appropriate suspension was developed for this application and improved by adjusting the additive composition. This study investigates the rheological behavior of screen printing inks and the corresponding topography of the printed layers. Rotary measurements were carried out to analyse the impact of shear rates on viscosity showing shear thinning behavior. In addition, oscillatory rheometry is performed to gain information about the viscoelastic properties of the slurries and to understand the internal structure of the developed inks. The viscoelasticity and the recovery behavior after shear loading are crucial for the topography of printed films.The principal investigations are executed on solvent-based suspensions, whereby the knowledge gained is used for a transfer to water-based systems allowing a more environmentally friendly handling.

In this study precursor derived SiOC/MoSi 2 composites were evaluated with respect to their potential for the application as glow plug material. In a first step, fully dense composite materials with different fractions of electrical conductive MoSi 2 were fabricated by field-assisted sintering technique (FAST). The percolation threshold, where the electrical properties change from insulating to a suitable level of conduction depends on the microstructure, which can be controlled by the initial particle size of the used SiOC particles. It becomes principally possible to fabricate both, the insulating part and the heater material with the same MoSi 2 content and therefore without thermal mismatch. Room temperature properties, high temperature strength, oxidation and creep behaviour depend strongly on the MoSi 2 volume fraction. MoSi 2 contents beyond the percolation threshold lead to significantly enhanced creep rates. At high temperatures, reactions between SiOC and MoSi 2 can be observed, which differ at the air exposed surface and in the interior of the samples. From these findings, an upper limit for the application temperature can be derived.

Glass-ceramics are often used as sealants in solid oxide fuel cells (SOFC). But interfacing components, such as ferritic stainless steel and YSZ electrolyte, may vary in their requirements regarding sealing properties, especially in terms of thermal expansion. A bilayered glass-ceramic system was developed to overcome the mismatch in coefficients of thermal expansion (CTE) between ferritic steel and YSZ. Therefore, two different glass-ceramics with slightly different CTEs were developed, one with good bonding characteristics to the ferritic steel and the other to the YSZ electrolyte. Steel and electrolyte components were coated with a layer of their corresponding glass sealant paste and heated up to form a sandwich sample. During the heat treatment of the sealing process, the glasses are crystallized into glass-ceramics. The resulting interface between the two glass-ceramics is of special interest. Cross-sections of the sandwich samples were cut, polished and investigated using SEM. The glass-ceramics show continuous, gap-free layers and excellent bonding to both steel and YSZ. Energy release rates are measured for single and bilayered glass sealants by mechanical testing. The designed bilayered glass-ceramics fulfill the special requirements of ferritic steel and YSZ. They show excellent potential to become a new outstanding sealant for SOFCs.