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High Temperature Aerogels for Thermal Insulation System

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Title: High Temperature Aerogels for Thermal Insulation System


1
High Temperature Aerogels for Thermal Insulation
System
  • Denisse V. Aranda
  • Mentor Dr. Fran Hurwitz
  • NASA Glenn Research Center
  • Structure and Materials

2
Overview
  • Objective
  • Introduction
  • - Properties
  • - Applications
  • Experimental
  • - Synthesis
  • - Characterization
  • Results and Discussion

3
Objective
  • To explore the use of high temperature aerogels
    in the development of lightweight, high
    temperature insulating materials and integrated
    structures for supersonic and hypersonic
    applications, including space exploration.

In my study To investigate the effects of solids
loading, ethanol content, molar ratio of Al/Si on
morphology, density, and thermal stability of
aerogels in the Al2O3 SiO2 systems
4
AEROGEL Worlds Lowest Density Solid !!
  • Aerogel is a low density solid-state
    material derived from gel in which the liquid
    component of the gel has been replaced with gas.
    An aerogel can be up to as much as 99.8 air!

5
Physical Properties
  • Rigid Foam
  • Mesoporosity
  • Hydrophilic
  • Friability
  • Low density
  • Air is 1.2 mg/cm3
  • Record-aerogel is 1.9 mg/cm3

6
Thermal Insulator
Conduction Since Silica is a weak conductor of
heat and electricity, silica aerogel make
incredibly good conductive insulators.
  • Convection
  • Since air cannot easily circulate throughout the
    lattice, aerogels make excellent convective
    insulators.

Thermal Radiation The most insulative aerogels
are silica aerogels with carbon incorporated
because the carbon absorbs the infrared radiation
that transfers heat.
7
TransparencyAerogels color is due to Rayleigh
scattering of the shorter wavelengths of visible
light by the nanosized dendritic structure.
8
Stardust
9
AEROGEL ON MARSAerogel was used as battery
insulation for the Mars Rover Pathfinder. This
allowed the rover to shed over 6 pounds which is
over 20 of the rovers weight !
10
Al2O3-SiO2 Phase Diagram Target compositions
81 AlSi
31 AlSi
11 AlSi
10 AlSi
11
Chemicals used in synthesis
TEOS (Tetraethoxysilane)
Aluminium Trichloride Hexahydrate
Propylene Oxide
Water
Ethanol
12
Formulations
  • Low Solids
  • Based on 48 total mmols

High Solids Based on 72 total mmols
Example 31 Ratio 3x1x 72 4x 72
x 18 mmol of Si 3x 54 mmol of Al
Example 31 Ratio 3x1x48 4x 48 x
12 mmol of Si 3x 36 mmol of Al
  • The full ethanol aerogels where made with 1302.36
    mmol EtOH while the half ethanol were made with
    651.18 mmol of EtOH.
  • All aerogels where made with 355.2 mmol of H2O
    and 311 mmol of Propylene Oxide.

13
SOL - GEL Chemistry
Supercritical drying
Hydrolysis
Condensation
Aerogel
Sol
Gel
14
Supercritical Dryer
Exchanges liquid ethanol for liquid CO2, then
takes it supercritical
Nino
Our Supercritical Fluid Extractor Technician
Chamber
Safe passage for gels from hydrogels to aerogels
15
Supercritical Fluid Extractor
Level Three - (fits 4 gels)
Level Two (fits 6-10 gels)
Level One (fits 6-10 gels)
16
Supercritical CO2 Fluid Extractor
By taking Carbon Dioxide to it supercritical
point (304.25 Kelvin, 73.96 bar), it can expand
as a gas but with the density of liquid.
17
Aerogel Structure
18
3D Statistical Modeling of Data
19
Shrinkage Model as a function Al/Si Ratio and
Ethanol
  • Lower ethanol content yields the minimal
    shrinkages in the aerogels
  • Molar ratios between 0.4 and 0.5 has the least
    shrinkages rates. (31 aerogels)

20
Shrinkage Model as a function Al/Si Ratio and
Solids Loading
  • Low solids (48 mmols) DECREASE in shrinkage as
    the molar ratio becomes more silica rich
  • High solids (72 mmols) INCREASE in shrinkage as
    the gels become more silica rich
  • Molar ratios between 0.3 and 0.4 has the least
    shrinkages rates.

21
FESEM(Field Emission Scanning Electron
Microscope)
22
Imaging Aerogel on Nanoscale
23
Morphology variation with Al/Si Ratio
  • High Al2O3 High SiO2
  • 10 81 41 3 1 11

24
Aerogel Composites
25
SiC Nanofibers
26
Al2O3 Electrospunfibers (Calcined to 700C)
27
Al2O3 Electrospunfibers (Calcined to 1050C)
28
Thermogravimetric Analysis (TGA)
Differential Thermal Analysis (DTA)
  • Samples retain 63 - 70 of their original
    weight
  • Crystallization occurs in a range from 980C to
    1320C

29
Characterizations Summary
  • Physical Density (Bulk Density)
  • 0.06g/cm3 - 0.18 g/cm3
  • Helium Pycnometry (Skeletal Density)
  • 1.2 g/cm3 1.9 g/cm3
  • BET (Surface Area)
  • 603 m2/g -778 m2/g
  • Nitrogen Desorption (Pore size)
  • 6.5nm 90 nm
  • Thermogravimetric Analysis (TGA)
  • 63-70 retained weight
  • Differential Thermal Analysis (DTA)
  • 980 C 1320 C
  • Percent Porosity
  • 88 - 96

30
Results and Conclusions
  • Shrinkages
  • Lower ethanol content paired with low solids
    loading yields the
    minimal shrinkages
    in the aerogels
  • Molar ratios between 0.4 and 0.5 has the least
    shrinkages rates. (31 aerogels)
  • Pore Size and Distribution
  • High Alumina and high Silica aerogels yield
    coarser pores while the intermediate Al/Si
    aerogels have the finer pores
  • Highest surface areas and narrowest pore size
    distribution occurs at molar ratios close to 0.4
  • Heat Capacity and Crystallization
  • Higher Alumina content increases the
    crystallization temperature
  • Ratios lower than 0.4 form mullite and alumina
  • Ratio greater than 0.4 (silica rich aerogels)
    form mullite and low temperature silica phases
    which creating volume changes upon
    crystallization as low as 575 C

31
Thank you NASA Glenn's Aerogel Team!
  • Dr. Fran Hurwitz My Mentor
  • Dr. Mary Ann Meador
  • Dr. Baochau Nguyen
  • Dr. Heidi Gou
  • Stephanie Vivod
  • Alia Hindi
  • Dan Scheiman
  • Anna Palzcer
  • Derek Johnson
  • Janet Hurst
  • Kevin Lamott
  • Dr.David Kankam
  • USRP Program
  • Dr. Ed Evans (U. Akron)
  • Rick Wiedenmannott

32
Thank you !
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