Mechanical Characterization of Solid Oxide Fuel Cells and Sealants

 
B 
BaO-CaO-SiO
2
- 
Al
2
O
3
Bars 
As-sintered 
Micro-
indentation 
RT 
77 ± 3
[83] 
Annealed 
77 ± 3
Joined
As-sintered 
86 ± 3
 
 
 
H-P 
Glass H + 20 wt % 
YSZ particles 
Sintered 
bars 
As-sintered 
Micro-
indentation 
RT 
73 ± 8
[83] 
Annealed 
79 ± 6
Joined 
bars 
As-sintered 
80 ± 15
Stack 
800°C for 
1056 h 
70 ± 12
[49] 
800°C for 
19000h 
100 ± 10
Bars 
As-sintered 
Impulse 
excitation 
~ 45
[65] 
4-points 
bending 
~ 40
H-Ag 
Glass H + 20 wt % 
Ag particles
Bars 
As-sintered 
Micro-
indentation 
RT 
75 ± 5
[83] 
Annealed 
74 ± 8
An influence of testing methods the data was found in previous studies [65, 118]. Zhao at al. 
reported different elastic modulus values [65] obtained from three testing methods on so-called 

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Literature review 
50 
H-P and B sealants, as shown in 
Figure
 3-33
. The results indicated a strong influence of the local 
morphology on the indentation test. Compared to the global values determined from bending and 
impulse excitation tests, the indentation test appears to be much more sensitive to porosity and 
homogeneity of the material. For a rather dense sealants such as the B glass-ceramic (almost 
non-porous), the different testing method yielded fairly similar results, while for a porous sealant 
such as H-P and H-Ag, the disagreement was quite obvious. Chang et al. [183] also obtained 
different values of elastic modulus for their GC-9 sealant using 4-points bending and ring-on-
ring test. They associated this difference to pores and defects that were associated with different 
specimen preparation [183]. The relationship between elastic modulus and increasing 
temperature has been discussed in their work for GC-9, indicating that the elastic modulus drops 
above 700°C. For the H matrix based sealants, the temperature dependency of elastic modulus 
was also investigated, which is discussed in detail in [65].
Figure 3-33: Comparison of elastic moduli obtained using different testing methods [65]. 
3.4.6.2.
Fracture stress (Bending stress) 
The fracture stress values of sealant materials similar to that considered in the present work are 
summarized in 
Table 
3-8
. Zhao [65] used bar-shaped and joined specimens to obtain the fracture 
stress of Jülich B and H-P type sealants by using 4-points bending test. The joined specimens are 
aimed to mimic the real case in the stack, by which much lower bending fracture stresses were 
obtained than in the case of sintered bars. Also sealant thickness effects were found for joined H-

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Literature review 
51 
P sealant specimens, i.e. the facture stress decreased with increasing thickness. Plenty of 
previous work [82, 136, 183, 184] reported that crystallization shows a positive effect on fracture 
stress of partially crystallized glass-ceramic sealants, while the growth and coalescence of micro-
voids and micro-cracks during the annealing can noticeably degrade the strength such as reported 
for the GC-18 sealant [185].
Instability issues might occur at operation relevant temperatures due to viscoelastic deformation 
of the residual glass phase. Most partially crystallized glass-ceramic sealants, such as H, H-P, 
GC-9, GC-18 show a non-linear behavior close to the glass transition temperature, while fully 
crystallized sealants (such as B sealant) showed relative stable fracture stress at elevated 
temperature.
Table 3-8: The fracture strength of the typical sealant materials. 
Glass sealant 
Specimen 
Conditions 
Test method 
Temp. 
(°C) 
Fracture 
strength (MPa) 
Ref. 
H 
BaO-CaO-SiO
2
, 
doped with Al
2
O
3
, 
B
2
O
3
, V
2
O
5
, ZnO
Joined 
As-sintered 
4-point 
bending 
RT 
52 ± 1 
[83] 
800 
~1 
B 
BaO-CaO-SiO
2
- 
Al
2
O
3
Bulk bars 
As-sintered 
4-point 
bending 
RT 
91 ± 12
[83] 
800 
~ 90 
Joined
As-sintered 
RT 
25 ± 2