New Compliant glass seal development at PNNL · 2014. 7. 28. · Compliant glass seal development...
Transcript of New Compliant glass seal development at PNNL · 2014. 7. 28. · Compliant glass seal development...
Compliant glass seal developmentat PNNL
12th SECA Workshop, Pittsburgh, PA, July 26-28, 2011
Y-S Matt Chou, E. Thomsen, J-P Choi, W. Voldrich,
and J. W. Stevenson
Introduction and objectives
Experimental: materials and test fixture
Q1: chemical compatibility study with YSZ coating
Q2: electrical stability under 0.8V loading
Q3: volatility evaluation in dual environment
Q4: validation in stack test fixture
This work is funded by US DOE SECA Core Technology Program
Compliant versus refractory sealing glass
2
Compliant sealing glass
0.00E+00
2.00E-03
4.00E-03
6.00E-03
8.00E-03
1.00E-02
1.20E-02
0 200 400 600 800 1000
stra
intemperature (oC)
YSO1 glass
Refractory sealing glass
Advantage: Disadvantage:
Low stress or relaxation, healing? metal-stable, narrow T window,
Wetting, volatile, reactive/corrosive?
Data provided by ORNL
850h aged
s = E a T
Crack healing
Commonly observed in glass at elevated temperatures.
3 mechanisms proposed: diffusion-driven thermal healing, adhesion from intermolecular forces, and chemical reaction at crack-tip
3
SCN-1 indented @ 2 kg Fired to 700oC held for 6min
Objectives
To conduct a comprehensive study of a commercial
compliant sealing glass in terms of thermal, chemical,
electrical, physical, and mechanical stability in SOFC
environments.
To apply compliant glass in stack test fixture for
validation.
4
Experimental: sample preparation
5
1. Thickness of spacer rings ~220 mm
2. SCN-1 glass mixed with ESL450 binder to form paste
AISI441
PEN
YSZ spacer ringsglass
Machined groove design
Spacer ring design
6
Experimental: stability and high-temp leak test
6
PEN cell or bilayer (1.4”f)
Al2O3 pipe
porous Al2O3 support
Inconel600 load block
(2”x2”) with incoming and
outgoing tubing
SCN-1 orAg/mica hybrid seal
with known leak rate
or plain Ag foils
Load (~12 psi)
He/H2 inHe/H2 out or to
pressure sensor
Compliant glass
Corrugated Ni-mesh
to mimic some
contact load
Al-SS441 (2”x2”x0.06”
with a central hole)
ZrO2 or mica ring
spacer
Microstructure of YSZ and Al2O3 coated SS441
7
Fe
Cr
Al
Zr
Q1: chemical compatibility with YSZ and Al2O3coated SS441 in dual environment at 750oC
8
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0 200 400 600 800 1,000
Leak
Ra
te (s
ccm
/cm
)
Time (Hours) @ 750oC
Test #35 Zirconia Coated 441 with machined groove SCN-1 sealed at 800°C/2hr leak rate
@ 750°C in 5% H2 perimeter sealed with Ag
0.2psi
0.5psi
1psi
0.00
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0.09
0.10
0 2 4 6 8 10 12
Leak
Ra
te (s
ccm
/cm
)
# deep thermal cycle
Test #35 Zirconia Coated 441 with machined groove SCN-1 sealed at 800°C/2hr leak rate
@ 750°C in 5% H2 perimeter sealed with Ag
0.2psi
0.5psi
1psi
Leak test during isothermal ageing Leak test during thermal cycling
SCN-1 glass showed good thermal and thermal cycle stability at 700, 750,and 800oC
Post-mortem analysis: glass/YSZ electrolyte interface near air side
9
Zr Si
KNa Ba
Post-mortem analysis: glass/YSZ coating interface near air side
10
SS441
Fe
Cr
Zr
Si
K
Na
Minimal crystallization during pure thermal cycling
11
800oC 20 cycles 750oC 20 cycles
Ceramic bi-layer
Ceramic bi-layer
Aluminized-441Aluminized-441
More crystallization during isothermal ageing
12
800oC/1000h plus 10 cycles 750oC/1000h plus 10 cycles
Ceramic bi-layer
Ceramic bi-layer
More crystallization during isothermal ageing
13
700oC/1000h plus 10 cycles: Ba-silicate and K-Al silicate
oxide mole%
Al2O3 1.84
BaO 3.57
CaO 3.96
Fe2O3 0.09
K2O 7.07
MgO 1.03
Na2O 7.83
TiO2 0.45
ZnO 0.01
ZrO2 0.01
Li2O 0.05
B2O3 0.03
SiO2 74.06
Alu
min
ized-4
41
Cera
mic
bi-la
yer
14
Q2: Electrical stability test
14
VV
VV
resistor
SS441
SS441
Inconel
Al2
O3
5%H2 in
+
+
-
-
sense
sense
out
out
+
+
-
-
sense
sense
out
Hybrid mica
SCN glassPower supply
And sensor
load
5%H2 out
15
Chemical compositions
15
SCN-1 glass Refractory glass
YSO77
oxide mole%
Y2O3 6.00
BaO 6.00
SrO 42.50
B2O3 10.00
SiO2 35.50
oxide mole%
Al2O3 1.84
BaO 3.57
CaO 3.96
Fe2O3 0.09
K2O 7.07
MgO 1.03
Na2O 7.83
TiO2 0.45
ZnO 0.01
ZrO2 0.01
Li2O 0.05
B2O3 0.03
SiO2 74.06
Alkali ions (Na+ and K+) are major charge carriers for conductivity in silicate glasses
Two concerns: liquid glassy phases, and alkali effect
16
Comparison of crystallized glass (YSO75) and less crystallized glass (G18) with as-received crofer
16
YSO75 @0.7V & 20%H2O, 2.7%H2/Ar (t<432hrs), 80%H2 (t>432hrs)
power outage @ ~700 h
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
0 200 400 600 800 1000 1200
hrs at elevated temperatures
oh
m-m
G18 @830oC
YSO75 @ 850oC20%H2O, 2.7%H2/Ar
20%H2O, pure H2
G18 (less crystallized compared to refractory glass) showed rapid decrease
In resistivity, suggesting dissolution/diffusion of metal ions from crofer22APU
17
Electrical stability with YSZ coated Aluminized SS441
17
Tested with flowing 5%H2 (~3%H2O) and a DC load of 0.8V across glass
Stable apparent resistivity (calculated by ohm x area/thickness neglecting coating
contribution) indicates coatings remain intact (compatible) with SCN-1 glass.
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
0 200 400 600 800 1000
resi
stiv
ity,
oh
m-m
hours
stability of YSZ coated aluminized SS441
800C
750C
700C
Microstructure of 800oC/1000h electrically tested sample with YSZ coating
18
YS
Z-4
41
YS
Z-4
41
glass
Chemical compatible with YSZ coating
19
No reaction and segregation of alkalis at interfaces under DC loading
SiZr
K
NaAl
electrical stability with plain SS441
20
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
1.E+06
0 100 200 300 400 500
Ap
pa
ren
t re
sist
ivit
y, o
hm
-m
hrs
SCN glass with as-received SS441 @0.8V 800C
750C
700C
Presence of Fe in SCN-1 glass
21
spot # O Na Mg Al Si K Ca Ti Cr Mn Fe Ba
1 67.09 26.46 0.35 4.90 1.20
2 65.41 13.52 0.84 19.43 0.51 0.29
3 66.89 0.63 0.25 1.55 27.67 1.92 0.14 0.14 0.53 0.29
4 64.84 2.24 0.61 1.54 24.90 3.32 0.86 0.70 1.00
5 65.83 0.95 0.31 1.28 28.26 2.04 0.37 0.10 0.38 0.48
6 64.44 2.43 0.69 1.25 24.84 3.17 1.23 0.15 0.50 1.31
12
34 (Fe=0.7%)
5
6 (Fe=0.5%)
Fe at%=0.06% SCN-1
22
Electrical stability with Aluminized SS441
22
1.00E+01
1.00E+02
1.00E+03
1.00E+04
1.00E+05
1.00E+06
0 100 200 300 400 500
resi
stiv
ity,
oh
m-m
hrs
SCN with aluminized SS441 @0.8V
800C
750C
700C
Tested with flowing 5%H2 (~3%H2O) and a DC load of 0.8V across glass
Stable apparent resistivity indicates coatings remain intact (compatible) with SCN-
1 glass.
Q3: volatility issue
23
Weight loss vs. time data provided by ORNL of SCN-1 pellets at 800oC in
stagnant air or flowing steam
Linear volatility rate (R) was averaged for 5000h (steam) or 10000h (air)
Test cond.
800oC
Avg. volatility
(g/mm2-hr)
Total wt. loss (%)
in 40,000h
YSZ-air 6.33x10-9 1.7
YSZ-steam 9.90x10-10 0.3
Al2O3-air 8.04x10-9 2.1
Al2O3-steam 1.08x10-9 0.3
Total weight loss %
= (R*L*T*40,000*100)/(r*L*T*W)
Q4: evaluate glass in stack test fixtures-thermal cycle stability
Objectives: thermal cycle stability, containment/spreading issue, and volatile species interaction in base-line stability for 1000h
Reasonable consistent OCV at 800oC (1.040 V) theoretical 1.048V over 10 deep thermal cycles (~50oC to 800oC in 3h, 800oC/3h, 18h to ~50oC).
24
0.7
0.8
0.9
1.0
1.1
0 50 100 150 200 250
OC
V, V
hrs
225H2, 225N2, 800 air, 31oC H2O
Q4: evaluate glass in stack test fixtures-containment/spreading issue
25
WF
PENFuel side
air side
glassFuel side Air side
glass
glass
Summary and conclusion
Compliant SCN-1 glass was evaluated comprehensively in thermal
cycles stability, thermal stability, and chemical compatibility with
candidate SOFC materials.
The glass demonstrated very good thermal cycle and thermal stability
with constant leak rate.
Interfacial characterization showed minimum reaction at YSZ
electrolyte and YSZ coating interfaces.
Electrical stability test under DC load indicated insulating nature of the
glass and no segregation of alkalis. Crystallization was similar as
1000h stability test without DC loading.
Volatility estimation indicated minimal glass loss in 40,000h operation.
Preliminary evaluation in stack test fixture showed good thermal cycle
stability without containment/spreading issue.
26
Future work
Optimize YSZ coating in terms of thickness with collaboration with modeling to stress minimization.
Evaluate stability (1000h) in stack test fixtures at various temperatures with emphasis on interaction of volatile species with active SOFC components.
Modify processing and sealing conditions to eliminate large pore formation.
Collaborate with modeling to predict microstructure evolution effect on compliance, thermal and physical properties.
Continue evaluating the spreading/containment issue, and predict the life-time flow under differential pressure.
Design new window frame for robust sealing.
27