Mechanical Characterization of Solid Oxide Fuel Cells and Sealants

 5-9
.
Figure 5-9:
 
SEM images of the electrolyte surface showing a) numerous micro-cracks and b) 
transgranular failure mode. 
5.1.2.7.
Fracture surface analysis 
Microstructural analyses were carried out in order to support fracture toughness analyses of 
anode substrate materials. Fracture surfaces of NiO-8YSZ (type 4) material were observed in the 
reduced state and re-oxidized state.
a) NiO-8YSZ tested at room temperature 
With respect to the failure mode, the fracture surface of NiO-8YSZ specimens indicated a mixed 
failure mode (
Figure
 5-10
). Similar findings on the failure mode of these material compositions 
have been reported in [143].

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Results and discussion 
86 
Figure 5-10: SEM images indicate a mixed mode failure of the NiO phase for a type 4 specimen.
b) NiO-8YSZ tested at 800°C 
After the 800 °C tests, SEM investigations revealed a higher amount of intergranular failure for 
NiO-8YSZ, however, it was not possible to be quantified (
Figure
 5-11
 ). This higher amount of 
intergranular failure at 800°C indicates that grain boundary fracture energy becomes lower 
compared to the fracture energy of the grains at elevated temperature. Nevertheless it can be 
concluded that, due to the small differences in values obtained at RT and elevated temperatures, 
the failure mode itself, i.e. trans- or intergranular does not permit any conclusion on the fracture 
toughness behavior.
Anode 
Anode 

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Results and discussion 
87 
Figure 5-11: SEM image revealed a mixed failure modes of NiO-8YSZ at 800°C (type 4).
 
The 
areas with white circles show transgranular failure mode examples, while intergranular mode 
examples are marked with red circles. 
c) Ni-8YSZ tested at room temperature 
In case of Ni-8YSZ, Ni particles showed pure intergranular failure (
Figure