Glenn Research Center at Lewis Field

NANO-CASTED METAL OXIDE AEROGELS

AS DUAL PURPOSE STRUCTURAL COMPONENTS

FOR SPACE EXPLORATION

Eve F. Fabrizio, Ph.D.

NASA Glenn Research Center

Materials Division/Polymer Branch

Brookpark, OH

2003-2004

Glenn Research Center at Lewis Field

Motivation For Research

Conductive

Magnetic

Light Emitters

•Electrical Conduits

•Sensors

Ultralightweight Strong

Structural components

Dual Purpose Materials

Metal Oxide Nano-casted

Aerogels

Glenn Research Center at Lewis Field

Overview

• Preparation of Metal Oxide Aerogels:

– Overall process and chemical reactions

• Characterization

– IR: Hydroxyl content vs. Carbonate content

– TGA: Thermal Stability, Phase Transitions

– DSC: Phase Transitions

– UV-VIS and Photoluminescence

– Surface Analysis: Area

– Skeletal Density

• Crosslinking Chemistries

Glenn Research Center at Lewis Field

Aerogels

nonporous

primary

particles

(<1 nm; dense silica)

mesopores

channels to

micropores

porous

secondary

particles

(density ~ 1/2 silica)

~5-10 nm

• Properties

– Low density (0.05-

0.5 g/cc)

– High porosity

– High surface area

(300-1000 m2/g)

• Uses

– Poor thermal conductors; Good insulators (see

picture)

– Good electrical insulators; SiO2-low dielectric <2

– Good electrical conductors; RuOx, VOx

– Photophysical properties; optics

– Sensors; Optical, Magnetic and Electronic

– Catalysts; High surface area increases

efficiency of reactions

Scanning Electron Microscopy

Silicon Dioxide Aerogel

Glenn Research Center at Lewis Field

MOx Aerogels Prepared

Gelled and Tested Attempted; No Gellation

Rare-Earth

Aerogels:

Focus

of this Study

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Silicon Dioxide Aerogels: Chemistry

Note: Same chemistry was used to prepare vanadium oxide aerogels.

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Silicon Dioxide Aerogels: Structure

O

Si

O

O Si

O

O

O

Si O Si O

OO

Si

O

Si

O

O

O

O

SiHO

SiHO

SiHO

OH

OHOH

OHSi

OHSi

OHSi

HO

HO

HO

OO O

Oparticle

particle

interparticle neck-zone

NC

O

NC

O

H[-O(CH2)4O2C(CH2)4CO-]n(CH2)3CH2O-H

poly(1,4-butylene adipate), diol end-capped

N

O

O

Structure of Silica:

Polyurethane chemistry:

carbamate

polyurethane

Desmodur N-3200poly(hexamethylene diisocyanate)

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Titanium Oxide Aerogels: Chemistry

Catalyst: HCl

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Overall Process for Preparing

Transition Metal Oxide Aerogels

aged gel

Native Silica Aerogels Silica / di-ISO Composites

MeOH /

Water

NH OH

sol

15 min

gel

aging

(48 h)

gel

aged gel

washed with

EtOH

and then

acetone

several

wash cycles

(2 days)

supercritical

drying (CO )

Native silica

aerogel monolith

sol

gel

oven (100 deg. C, 3 days)

supercritical

drying (CO )

di_ISO cross-linked silica

aerogel monolith

gel washed with EtOH

then propylene carbonate

di-ISO in

propylene

cabonate

(4 washings)

4

2 2

TMOS in

MeOH

MeOH /

Water

NH OH4

4 washings with

acetone

Glenn Research Center at Lewis Field

Metal Oxide Aerogels: Transition Metals

(in ethanol) (age for 72 hrs)MClx

. 6H2O MOx

O

Cl

a)

M

O

HH

O

Cl M

O

H

O

Cl

H

++

b) O

Cl

H

M

Cl

M

OH

ClHO

+ +

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supercritical

drying (CO2)

Overall Process for Preparing

Transition Metal Oxide Aerogels

MClX · 6 H2O

in CH3CH2OH

O

Cl

MOx GelPour into molds and

Aged for 72 h

Gels washed 4 times

with CH3CH2OH

Gels washed

4 times

with CH3CN

CharacterizationIR,TGA,DSC,Density

Surface Area

Glenn Research Center at Lewis Field

Transition Metal Aerogels: Structure

YOx GdOx ErOx

YbOx FeOx RuOx

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Characterization of Rare-Earth Aerogels

MOx

Density

(g/cc)

Skeletal

Density

(g/cc)

Surface

Area

(m2/g)

Average

Pore

Diameter

(A)

labs,max

(nm)

lex,max

(nm)

Magnetic

Susceptibility

PrOx 0.18 2.82 186 84 (< 300) None N/A

NdOx 0.19 3.13 384 109 582 None N/A

SmOx 0.22 2.97 383 93 (<300) None N/A

EuOx 0.20 2.47 379 77 394 616 N/A

GdOx 0.18 3.14 383 72 (<300) None N/A

TbOx 0.20 3.32 365 88 (<300) None N/A

DyOx 0.18 3.02 N/A N/A (<300) None N/A

HoOx 0.21 2.47 N/A N/A 451.5 None N/A

ErOx 0.16 3.28 368 89 520/523 None N/A

TmOx 0.14 3.17 N/A N/A (<300) None N/A

YbOx 0.15 3.25 345 79 291.5 None N/A

SiO2 0.18 1.77 500-1000 14 None None N/A

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Absorbance and Photoluminescence of EuOx

0.5

1

1.5

2

2.5

3

3.5

4

4.5

300 1300 2300

wavelength (nm)

ab

sorb

ance

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0.5

470 570 670

wavelength (nm)

em

issio

n in

tensity

lex. = 394 nmabsorbance transistion

used for excitation

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Iron Oxide Aerogel

Low Density Magnetic Material

Native

Aerogel

Crosslinked

with di-isocyanate

Crosslinked aerogel

sinter until magnetic

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Process to Crosslink Metal Oxide Aerogels

supercritical

drying (CO2)

MOx gelPour into molds and

aged for 72 h(Amine modified gels

were prepared with

aminopropylsilane and

No base catalyst)

Gels extracted from

mold and washed

4 times

with solvent for

cross-linking

Gels placed in

monomer solution

and crosslinked:

D or Initiator

Gels washed

4 times

with solvent for

supercritical drying:

Acetone or

Acetonitrile

Characterization

of final gel; physical,

chemical and spectral

Glenn Research Center at Lewis Field

Crosslinking Chemistries: Polyurethane

Si-OH OCN R NCO+ Si-O C

O

NH

R NCO

Si-O C

O

NH

R NCOH2O

Si-O C

O

NH

R NH2

Si-O C

O

NH

R NH2 OCN R NCO+

Si-O C

O

NH

R NH

C

O

NH

R NCO

adsorbed on silica

+ CO2

carbamate

urea

+ H2O, etc.

silica

Glenn Research Center at Lewis Field

Additional Crosslinking Chemistries

NH

NH

NH

O

O

O O

O

O

O

O

O

O

O

O

O

O

O

NH2

NH2

NH2

O OO O

Secondary particle

NH

NH

NH

O

O

O O

O

O

O

O

O

O

O

O

O

O

O

NH2

NH2

NH2

O OO O

NH

NH

NH

O

O

O O

O

O

O

O

O

O

O

O

O

O

O

NH2

NH2

NH2

O OO O

NHNH

NHNH

NHNH

O

O

O O

O

O

O

O

O

O

O

O

O

O

O

NH2NH2

NH2NH2

NH2NH2

O OO O

Secondary particle

2 Si-(CH2)3-NH + n

Si-(CH2)3-NH NH-(CH2)3-Si

n-1

AIBN

DH

Polystyrene

linkage

2 Si-(CH2)3-NH + n

Si-(CH2)3-NH NH-(CH2)3-Si

n-1

AIBN

DH2 Si-(CH2)3-NH + n

Si-(CH2)3-NH NH-(CH2)3-Si

n-1

AIBN

DH

Polystyrene

linkage

Epoxies

PolystyreneSi-(CH2)3-NH2 + Si-(CH2)3-NH

Aminopropyl groupSecondary

particle

Cl

Styrene

Si-(CH2)3-NH2 + Si-(CH2)3-NH

Aminopropyl groupSecondary

particle

Cl

Styrene

Cl

StyreneStyrene

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Silicon Dioxide Aerogels Crosslinked with Di-isocyanate

(Bayer’s Desmodur N3200)

Native

AerogelNative Aerogel

Cross-linked Aerogel

Glenn Research Center at Lewis Field

Vanadium Oxide Aerogel Crosslinked with a Di-

Isocyanate (Bayer’s Desmodur N3200)

Native gel

Crosslinked VOx Aerogel

Glenn Research Center at Lewis Field

Results and Conclusions

• The following Rare-Earth Gels were prepared:

From all these metals, two were unsuccessful

La- very fragile (unable to remove from mold)

Ce-precipitated prior to gelling

• For most, structure similar to the silica aerogels with some differences:

– more macroporous than microporous

– skeletal density greater and pore diameter higher

• Analysis by IR,TGA and DSC determined the presence of carbonate in the native rare earth gels.

• Carbonate formed during the supercritical drying: impact on crosslinking to be determined

• All gels were successfully crosslinked using di-isocyanate and are presently being characterized for chemical, physical and structural properties.

Tb HoDyPr Nd Sm Eu Gd Er TmYb LuLa Ce

Glenn Research Center at Lewis Field

Acknowledgements

• Plousia Vassilaras (LERCIP)

• Anna Palczer (GRC)

• Linda McCorkle and Faysal Ilhan,

Ph. D. (OAI)

• Nicholas Leventis, Ph.D. (GRC)

• Ohio Aerospace Institute (OAI)

• Polymer Branch/NASA Glenn

Research CenterDemonstration of the insulating

properties of aerogels