influence of aerogel morphology and reinforcement ......1100˚c, 24h 1100˚c, 48h 1100˚c, 96h...
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InfluenceofAerogelMorphologyandReinforcementArchitectureonGasConvectioninAerogelComposites
FrancesI.Hurwitz1,MatthewMeyer2,Haiquan Guo3,RichardB.Rogers1, JeffreyDeMange4,HayleyRichardson2
1NASAGlennResearchCenter,Cleveland,OH441352UniversitiesSpaceResearchAssociation(USRA),Cleveland,OH441353OhioAerospaceInstitute,Cleveland,OH441424UniversityofToledo,Toledo,OH43606
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Background:• Aerogels are very effective insulators, primarily in
suppressing heat transfer by gas convection, but also in providing a tortuous path for solid conduction.
• Alumina and aluminosilicate aerogels can maintain mesoporous structure to temperatures of up to 1200˚C.
• These aerogels are fragile, but an be reinforced with fabrics, papers or foams to form composites in which the aerogel serves as the matrix.
Objective:Characterize gas permeability of aluminosilicate aerogels with various ceramic fabric, paper or felt reinforcements.
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AlO6 octahedra S.Brühne,Cryst.GrowthDes.,2008,8(2),pp 489–493n
Boehmite [AlO(OH)]
Synthesis Approach: Boehmite alone to form alumina aerogel; Boehmite + TEOS co-condense to form aluminosilicate.
+
TEOS
hydrogel aerogelsupercriticalCO2
P.R.Aravind,etalMicroporous andMesoporous Materials96 14–20(2006).
Introduction of silica into alumina lattice inhibits transformation to α-alumina(Hurwitz, et al., manuscript in preparation)
Si OOO
O
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1100˚C, 24h 1100˚C, 48h 1100˚C, 96h
1200˚C, 24h
As supercritically dried
Micrographs showing persistence of mesoporous structure within aluminosilicate aerogel heated at 1100 and 1200˚C.
600˚C, 24h
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CeramicReinforcement
Thickness(mm)
Density(g/cm3)Asreceived
CompositeDensity(g/cm3)
UpperUseTemperature Composition(%)
Astroquartz (503plainweave)Unsized
0.11 0.95 0.610-0.997 1070° C 99.99SiO2
Nextel440 0.3 1.0 1.09 1100-1200˚C γ-alumina +mullite +amorphousSiO2
ZYW30A
Saffil Paper 0.5,1.0 0.15(wbinder)0.125(1000C) 0.144-0.194 1600° C95-97Al2O3,3.0-5.0SiO2,
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Aerogel impregnation into woven fabrics fills crossover points between tows as well as inter-fiber spacing within tows, decreasing gas permeability.
Example shown in Astroquartz503 (plain weave)
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2-D Fabric composites
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APA-2/ aerogel composite
Density of 0.14 g/cm3, lighter than Microtherm HT (0.3428g/cm3)
Aerogel bonds to fibers; unlike commercial materials, particles do not spall. Aerogel/fiber bond achieved by heat treatment of alumina paper to remove all binders prior to sol impregnation.
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APA-1, binder removed
APA-2, no organic binder (inorganic may include Si, S, Ba, K,Ca)
Saffil paper, binder removed
Saffil paper, 1000˚C
inorganic
silica
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Fiberfrax 972AH
47-52 Al2O3, 48-53 SiO2,
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Reinforcement Massfractionaerogel
Astroquartz 0.10
Nextel440 0.05
ZYW30A 0.06
APA-2 0.37
Saffil 0.30
Fiberfrax 0.28
Quartzpapers 0.52-0.62
Quartzfelt 0.6-0.9
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Astroquartz
0
10
20
30
40
50
60
0 0.2 0.4 0.6 0.8
Airflow(C
FM/SF)
DifferentialPressure,in.H2O
Astroquartz Comparison
AQ1fabric
AQ2fabric
AQ4composite
AQ38composite
43.4
37.4
0.557 0.1530
5
10
15
20
25
30
35
40
45
50
Airflow(C
FM/SF)
Astroquartz503permeabilityat0.50in.H2O
AQ1fabric
AQ2fabric
AQ4composite
AQ38composite
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AF10withsizing (left)andwithoutsizing(right).
BF10withoutsizing BF20withoutsizing
Nextel fabrics
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13
0
50
100
150
0 0.2 0.4 0.6 0.8
Airflow(C
FM/SF)
DifferentialPressure(in.H2O)
Nextelfabrics
N440BF10w/sizingN312AF10w/sizingN312AF-10w/osizingN440BF-10w/osizingN440BF-20
52.62
1.15
31.75
0.35
11.14
0.340
10
20
30
40
50
60
70
Airflow(C
FM/SF)
ComparisonofNextelweavesw/osizingandtheircompositesat0.50in.H2O
N312nocompositeN312CompositeN440BF10nocompositeN440BF10compositeN440BF20nocompositeN440BF20composite
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14
14
0
20
40
60
80
100
120
0 0.2 0.4 0.6 0.8
Airflow(C
FM/SF)
DifferentialPressure(in.H2O)
Saffil papercomparison
.5mmpaperwithsizing
1mmpaperwithsizing
SP1151mmwithoutsizing1000C
SP1181mmwithoutsizing1000C
SP1710.5mmwithoutsizing600C
SP1621mmwithoutsizing600C
SP1611mmwithoutsizing600C
0100200300400500600700800
0 5 10 15
Airflow(C
FM/SF)
DifferentialPressure(in.H2O)
Saffil0.5mmpaperandcomposites
.5mmpaperwithsizing
SP171.5mmwithoutsizing600C
SP143.5mmcomposite1000C
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 5 10 15
Airflow(C
FM/SF)
DifferentialPressure(in.H2O)
Saffil 0.5mmcomposites
SP173.5mmcompositenopreheattreatment,600Cposttreatment1600-3.5mmcompositenopreheattreatment,noposttreatmentSP143.5mmcomposite1000C,600Cposttreatment
Note variations in scale!
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0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 2 4 6 8 10
Airflow(C
FM/SF)
Sensor1DifferentialPressure(inH2O)
APA2Comparison(0.5mmnozzle)
APA2-658paper
APA2-648Composite
APA2-653Composite
APA2-654Composite
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024681012141618
0 2 4 6 8 10
Airflow(C
FM/SF)
Sensor1DifferentialPressure,inH2O
Fiberfraxcomparison
972AHasreceived
972AH-41composite
Incorporation of aerogel provides marked reduction in permeability for both papers, but APA2 paper has much lower permeability than Fiberfraxpaper alone.
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0
10
20
30
40
50
60
70
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Airflow(C
FM/SF)
DifferentialPressure(in.H2O)
Wovenfabriccomparison
N312AF-10
Astroquartz503
N440BF-10
ZYW30A
N440BF-20
16
0
20
40
60
80
100
120
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7
Airflow(C
FM/SF)
DifferentialPressure(in.H2O)
PapercomparisonAPA2
Saffil0.5mmw/osizing
Saffil0.5mmw/sizing
Saffil1mmw/osizing
Saffil1mmw/sizing
Fiberfrax972AHasreceived
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17
40.4
52.62
31.75
11.1421.9
72.48
13.9
95.45
0
20
40
60
80
100
120
Airflow(C
FM/SF)
Comparisonofnon-compositematerialsw/osizingat0.5inwater
Astroquartz
Nextel312AF10
Nextel440BF10
Nextel440BF20
ZYW30A
Saffil1mmpaper
Fiberfrax972AH(wbinder)
APA2
Saffil 0.5mmpaperw/obinderwastoofragiletobetestedat0.50in.H2O.
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0.355
0.574
0.354 0.342
0.098
0.292
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8Airflow,CFM
/SF
Comparisonofwovenfabriccompositesat0.50in.H2O
AstroquartzComposite
N312AF10composite
N440BF10composite
N440BF20composite,noposttreatmentN440BF20composite,600C
ZYW30Acomposite
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0.066
0.15
0.260.24
0.08
0.19
0.11
0
0.05
0.1
0.15
0.2
0.25
0.3
Airflow,CFM
/SF
Comparisonofpaperandfelt/aerogelcompositesat0.50in.H2O(extrapolated)
APA2
Saffil0.5mmcomposite,1000C/600CSaffil0.5mmcomposite,none/600CSaffil0.5mmcomposite,none/noneSaffil1mmcomposite
Fiberfrax972AHcomposite
Quartzelcomposite
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Hydrophobic treatments availableUse of PTMS shows some reduction of surface area at high temperature.Some additional silica incorporation occurs; PTMS does not produce cristobalite seen with other silanes.
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050100150200250300350400450
0 400 800 1200 1600
BETsurfaceaream
2/g
Time,min
Untreated,asdriedaerogelUntreated,600C
Untreated,1000C
Untreated,1100C
Untreated,1200C
PTMS,600C
PTMS,1000C
PTMS,1100C
PTMS,1200C
cristobaliteδ,θ
21-22˚-amorphous hump
mullitemullite
mullite
X-ray Diffraction of Hydrophobic Samples Heated at 1200C, 24h
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Trades:
• Woven fabrics incorporate low fraction of aerogel, but can reduce gas permeability, reducing convective heat transfer.
• Alumina fiber provides opacification; alumina papers offer best thermal performance.
• Saffil paper contains some small silica fibers which bridge fiber cross-over points on heating to 1000˚C, stiffening paper. Aerogel composite thermal properties and permeability are comparable to APA-2. Saffilavailable as 0.5 mm paper, thinner than 1 mm APA-2, and therefore slightly more flexible.
• Fiberfrax 972AH offers highest flexibility, but slightly higher thermal conductivity and permeability and contains respirable fiber. (APA-1 and Saffil also contain small diameter fibers). Most flexible, particularly with “slip” layer.
• Quartz felts offer highest aerogel incorporation on a volume fraction basis (fiber volume fraction is low), and offer lowest density and more robust mechanical strength than many of the papers.
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Conclusions:
• In 2-D fabrics, weave architecture strongly influences permeability. Removal of organic sizing permits spreading of tows to reduce gas flow.
• Impregnation of 2-D fabrics with aerogel provides more than an order of magnitude reduction in permeability. N440 (BF20) provided lowest permeability of options tested, but is a heavy option (1.1 g/cm3).
• Ceramic papers generally offer further reduction in permeability and lighter weight than fabrics, but are more fragile mechanically, and composites of most papers are less flexible than the 2-D weaves.
• Waterproofing techniques have been developed; however, influence on permeability has not as yet been evaluated.
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