Mechanical Characterization of Solid Oxide Fuel Cells and Sealants

particles and crystallites. An elemental mapping (in 
Figure
5-26
 
(a)
) verifies that there is no 
excessive reaction layer at the interface between sealant and steel. After 500 h annealing (
Figure
 
5-25
 (
b)
) the silver particles deformed and appeared to shrink. A respective elemental mapping 
in 
Figure 5-26
 (
b)
indicates that there is no significant change in the elemental distribution. The 
amount of dark grey crystallized phases (79 %) in annealed sealant increased significantly 
compared to the as-sintered state (46 %) (see also [65]). An additional complementary EDX 
focusing onto the interface of sealant and steel revealed a very thin oxidized steel layer (
Figure 
5-26
 
(
c)
). Also the XRD analysis of the annealed state (
Figure 
5
-
27
(
b)
) confirmed that the 
crystalline phase significantly increased after annealing, compared to as-sintered H-Ag (
Figure 
5-27 
(a)
).
a) 
b) 
Figure 5-25: Microstructure of (a) as-sintered H-Ag and (b) annealed H-Ag. 

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Results and discussion 
107 
a) 
b) 
c)
Figure 5-26: Elemental mapping of (a) as-sintered H-Ag; (b) and (c) annealed H-Ag. 

---

Results and discussion 
108 
a) 
b)
Figure 5-27: XRD patterns of (a) as-sintered H-Ag and (b) annealed state. 
(2) H-F
Figure
5-28
illustrates the microstructure of the sealant H-F after 10 h joining and 1000 h 
annealing at 850°C, respectively. The microstructure consists of white YSZ fibers and black 
pores and the residual glassy phases. In fact, the sealant material appears to consist mostly of 
residual glassy phases; crystallized phases are almost absent. Microstructure in an annealed state 
shows an apparently higher amount of crystalline phases as shown in the bright phases in 
Figure 
5-28
 (
b)
. It has also been reported that the fraction of crystallized phase is only around 8%, after 

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Results and discussion 
109 
500 h annealing treatment, the crystallization is enhanced to ~ 25% [83]. The XRD patterns 
before and after 500 h annealing are shown in 
Figure
 5-29
. 
a)
b)
Figure 5-28: SEM image of H-F sealant materials with 850°C for (a) 10 hours joining, (b) 1000 
hours annealing. 
a)

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Results and discussion 
110 
b)
Figure 5-29: XRD patterns of (a) as-sintered H-F and (b) 500 h annealed state [83]. 
(3) 7.5 B(Ba)
The microstructures of as-sintered and annealed (800°C for 800 h) sealant 7.5B(Ba) are shown in 
(b)
clearly shows 
the phases in the microstructure, where the white areas are barium silicate, the dark needle-shape 
areas are BaMa
2
Si
2
O
7
and the dark amorphous areas correspond to residual glassy phase as 
identified via complementary spot elemental analysis by EDX at CSIC, Madrid, Spain. After 800 
h annealing treatment, a slightly increased porosity related to crystallization shrinkage can be 
seen and, with respect to the phases (see(d)
), barium silicate is again visible without 
a defined stoichiometry as bright area, however, these phases seem to increase considerably in 
size and in proportion compared to the as-sintered state. Despite the increased amount of these 
barium silicate phases, the dark needle-shape phase BaMg
2
Si
2
O
7
is present as majority in the 
composition.

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Results and discussion 
111 
a) 
b)
c) 
d)