Stabilität und Kompatibilität des keramischen Interkonnektors der Hochtemperatur-Brennstoffzelle SOFC

Solid oxide fuel cells are operated at temperatures from 1073 K to 1273 K due to the use of ceramic materials as solid electrolyte. In view of the high temperatures and the required long operating times of at least 40000 hours particularly great demands are made on the stability and chemical compatibility of the materials used. The aim of the present work is to conduct relevant studies of the ceramic LaCrO$_{3}$ - based interconnect in order to provide a contribution to its further development. Moreover, these studies contribute towards a better understanding of the mechanisms which can lead to a deterioration of the function of SOFC modules. Apart from the investigation of the defect thermodynamics, the influence of the formation of defects on the mechanical properties of the partially substituted materials based on lanthanum chromite is studied in more detail. The kinetics of defect formation complements the spectrum of these studies. The chemical interactions between the materials used in the SOFC were studied under the conditions prevailing during cell operation. The formation of phases was determined by X-ray diffraction analysis. Ca-containing lanthanum-chromite specimens of different composition currently considered as candidate materials for the ceramic interconnect were prepared and characterized. For comparison, two material grades produced for technical application were incorporated in the investigation programme. These were the ceramic interconnect materials La$_{0.80}$Sr$_{0.20}$Cr$_{0.97}$V$_{0,03}$O$_{3-\delta}$ and LaCr$_{0.78}$Mg$_{0.05}$Al$_{0.16}$O$_{3-\delta}$. Equilibrium constants for the formation of oxygen vacancies in the above-mentioned lanthanum chromites were determined by thermogravimetry. The parameters for establishing disorder equilibria in the Ca-doped specimens resulted from kinetic measurements which were also performed with the aid of the thermobalance set up. The mechanical studies tonfirm an increase in fracture toughness, strength and Young's modulus with diminishing oxygen partial pressure, i.e. increasing amount of oxygen vacancies