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Development and testing of sealing glasses for SOFCs based on CFY-interconnects

 
: Rost, Axel; Schilm, Jochen; Suffner, J.; Kusnezoff, Mihails; Michaelis, Alexander

Kusnezoff, Mihails (Scientific Advisory Committee) ; European Fuel Cell Forum -EFCF-:
11th European SOFC & SOE Forum 2014. Proceedings and additional information. CD-ROM : 1 - 4 July 2014, Kultur und Kongresszentrum Luzern, Lucerne, Switzerland
Luzern-Adligenswil: European Fuel Cell Forum, 2014
ISBN: 978-3-905592-16-0
Paper A1404, 10 pp.
European Solid Oxide Fuel Cell Forum (SOFC) <11, 2014, Luzern>
International Solid Oxide Fuel Cell and Electrolyser Conference <2014, Luzern>
English
Conference Paper
Fraunhofer IKTS ()

Abstract
For a reliable and safe operation of Solid Oxide Fuel Cells (SOFCs), gastight sealings with high long-term stability are required. Due to stringent demands to the sealing materials resulting from working temperatures up to 900 °C, harsh atmospheres and the need of electrical insulation, only few materials are suitable for this application. Among the different sealing concepts, still the most common used is to apply sealings with glasses or glass ceramics. Glass sealings are related to rigid joints forming chemical bonds with joined components. Therefor the thermo-physical properties of sealing material have to be adapted to these materials. This was realized by a glass forming system of BaO-SiO2-Al2O3 with additional oxides for controlling crystallization of disilicate-type phases. They are needed to adjust the coefficient of thermal expansion, the viscosity for sealing and reactivity during operation. The general aim was to develop partial crystallizing glass ceramics with residual glassy phases maintained during stack operation for relaxation of mechanical stresses. This study presents the development of sealing glasses for SOFC-stacks based on CFY-interconnects (Cr, Fe, Y) produced by PLANSEE SE. It is shown that relevant properties of the CFY-alloy such as thermal expansion and chemical compatibility are matched by adjusting the composition of the glasses. With respect to the high Cr-content of CFY the chemical compatibility of the glasses was investigated with a unique setup for in-situ measurements of the resistivity of sandwich type samples at high temperatures in a dual atmosphere under applied voltage up to 5 V. SEM investigations of interfacial reaction layers of tested samples gave valuable information for the optimization of the glass compositions. Special interest was paid to the formation of chromate-type oxides which are known to have detrimental effect on the adhesion of the sealing glasses on metallic substrates. As a consequence sealing glasses with minimized BaO-contents leading to a controlled crystallization behavior have been created. Further testing of selected BaO-containing and BaO-free glasses was performed in SOFC stacks to characterize the joining behavior under realistic conditions. Results obtained from testing of model samples and from sealed and operated CFY-stacks were in good agreement showing possibility to apply the developed methodology for ex-situ glass material development.

: http://publica.fraunhofer.de/documents/N-341441.html