Mechanical Characterization of Solid Oxide Fuel Cells and Sealants

---

Mechanical Characterization of Solid Oxide
Fuel Cells and Sealants
 
Mechanische Charakterisierung
von Hochtemperaturbrennstoffzellen und Dichtungssytemen 
Von der Fakultät für Maschinenwesen der Rheinisch-Westfälischen Technischen Hochschule 
Aachen zur Erlangung des akademischen Grades einer Doktorin der Ingenieurwissenschaften 
genehmigte Dissertation
vorgelegt von 
Jianping Wei
Berichter: Univ.-Prof. Dr.-Ing. Lorenz Singheiser 
Univ.-Prof. Dr.-Ing. Tilmann Beck 
Tag der mündlichen Prüfung: 05. 09. 2016 
„Diese Dissertation ist auf den Internetseiten der Universitätsbibliothek online verfügbar.“ 

---

Abstract 
Solid oxide fuel cells (SOFCs) have a high application potential due to the evolved demands in a 
global energy network. Characterization of thermo-mechanical aspects, in particular elastic, 
fracture and creep behavior of sealants and anode substrates, is essential to warrant reliable 
production and operation of planar SOFCs. In this respect, several mechanical parameters have 
been determined and analyzed to get insight into the mechanical behavior and possible issues for 
joining, thermal cycling and long term reliability of SOFC stacks and systems.
For anode substrates, facture toughness and creep behavior as major mechanical aspects were 
studied. In this respect, the room and elevated temperature fracture toughness of two typical 
anode substrate variants (NiO-3YSZ and NiO-8YSZ) were characterized in oxidized and reduced 
state, some selected tests were concluded for a re-oxidized state. Elevated temperature creep 
studies concentrated on Ni-8YSZ composites with different porosities, where different loading 
configurations have been compared to assess effects of compressive and tensile stresses. The 
interpretation and analysis of the data were based on analytical and finite element analysis. 
Leakage of sealants will lead to a malfunction of the entire system, hence the structural integrity 
of sealants is crucial for a reliable operation of SOFC stacks and systems. In particular, Ag 
particle and YSZ fiber reinforced sealants, based on a glass matrix material developed in Jülich, 
were studied in stack operation relevant as-sintered and annealed state. Sealants supplied by 
Ceramics and Glass Institute (CSIC, Madrid, Spain) were also characterized and compared. 
Work concentrated on characterization of fracture stress at elevated temperatures on specimens 
mainly in a head-to-head geometry and complementary torsion tests to investigate the shear 
strength. The results of mechanical analysis were supported by advanced microstructural 
characterization and fractography to gain insight into annealing and filler reinforcement effects.

---