Mechanical Characterization of Solid Oxide Fuel Cells and Sealants

 4-3
 presents a schematic and real joined plate specimen.
Figure 4-3: Schematic and real joined plate specimen.
 
4.2.
Microstructural characterization 
4.2.1.
Microscopy 
Selected specimens were embedded in epoxy resin and ground with SiC abrasive papers up to 
4000 grit. Subsequently, polishing was performed using diamond paste up to 0.25 μm grain size. 
The microstructure of all materials was investigated using optical microscope (CSM, Switzerland) 
and scanning electron microscope (LEO 440, Zeiss Merlin, INCAEnergy). Element analysis was 
carried out using energy-dispersive X-Ray spectroscopy (EDX, Inca, Oxford).
The porosities of the initial NiO-YSZ and the material in the reduced state were investigated. 
Porosity was graphically analyzed with the ImageAnalysis Pro® software using the planimetric 
method. The pore percentage was obtained from the ratio of the pore area to the total area of 
microstructure image. Fractography to assess fracture origins was carried out using stereo-

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Experimental 
60 
microscope (Olympus SZH10) and scanning electron microscope (LEO 440, Zeiss Merlin, 
INCAEnergy).
4.2.2
X-ray diffraction 
X-ray diffraction is an effective tool for the investigation of the phase transformations. The 
principle is based on the change of the crystal lattice parameter α. The lattice parameter depends 
on the atomic species presented in a particular material. The phase analysis in this work was 
performed by X-ray diffraction using a Siemens D5000 diffractometer, which is equipped with 
an X-ray tube with copper anode (λ=1.5418 
𝐴̇
). The step scan used Cu-Ka radiation with a step 
size 0.02° and a step time 5s.
4.3.
Mechanical characterization
4.3.1.
Fracture toughness 
Double torsion tests as an effective method to measure fracture toughness were carried out on 
various anode materials in this work. The anode materials in oxidized and reduced states were 
tested at room temperature in air and typical operation temperature (800°C) in a 4 % H
2
/Ar 
atmosphere, respectively. The temperature was monitored close to the outer specimen surface 
with a thermocouple type K. The specimens were tested in a full ceramic double-torsion (DT) 
set-up placed in an Instron 1362 machine. Initially the specimens were loaded with 1 N pre-load 
and further applied the specimen with the controlled constant displacement rates. A schematic 
image of a DT setup is shown in 
Figure