Mechanical Characterization of Solid Oxide Fuel Cells and Sealants

3-31
. The results shown in 
Figure
 3-32
 (a)
indicate 
that the creep rate of the Ni is faster than that of 3YSZ and 8YSZ by 9 and 7 orders of magnitude, 
respectively. The similar strain rates (
Figure
3-32
 
(b)
) of porous Ni-8YSZ and porous 8YSZ 
indicated that the YSZ phase is essentially carrying most of the applied load. Experimental tests 
were carried out in the current work to verify these conclusions.

---

Literature review 
48 
Figure 3-31: Finite element mesh of reconstructed microstructures. The Ni and YSZ phases 
colored white and grey, respectively [44]. 
Figure 3-32: (a) Creep rate of Ni, 3YSZ and 8YSZ at 800°C for the relevant stress range; (b) 
volume-averaged strain in the loading direction [44]. 
If pores are present, the measured creep rate should differ from that of a theoretically dense 
material. Due to the pores the effective stress is larger than the applied stress. It has been 
reported for example in [181, 182] that the steady-state creep rate of polycrystalline ceramics 
(e.g. Li
2
O-ZnO-SiO) increases with increasing porosity.
In this work, different loading configurations were applied to assess the influence on creep 
behavior of materials, considering also porosity and Ni/YSZ composition effects.

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Literature review 
49 
3.4.6.
Mechanical properties of sealants 
3.4.6.1.
Elastic properties
During recent years glass-ceramics of the BaO-CaO-SiO
2
system were mostly used in SOFC 
stack assembling [65]. Elastic moduli of various sealant materials were investigated and 
discussed in previous studies [49, 65, 82, 83, 118]. 
Table
3-7
compiles the data along with the 
corresponding testing temperature and method.
Table 3-7: Elastic moduli of typical SOFC sealant materials. 
Glass-ceramic 
sealant 
Specimen 
Conditions 
Test method 
Elastic modulus 
(GPa) 
Ref. 
GC-9 
BaO-SiO
2
-B
2
O
3
-
Al
2
O
3
, ZrO
2
, La
2
O
3
 
Bars 
As-sintered 
4-points 
bending 
66 ± 8 
[183] 
Annealed 
68 ± 6 
plate 
As-sintered 
Ring-on-ring 
18 ± 6 
[184] 
Annealed 
19 ± 4 
H 
BaO-CaO-SiO
2
, 
doped with Al
2
O
3
, 
B
2
O
3
, V
2
O
5
, ZnO
Bars 
As-sintered 
Micro-
indentation 
RT 
72 ± 5
[83] 
Annealed 
80 ± 9