Title: High Temperature Aerogels for Thermal Insulation System
1High Temperature Aerogels for Thermal Insulation
System
- Denisse V. Aranda
- Mentor Dr. Fran Hurwitz
- NASA Glenn Research Center
- Structure and Materials
2Overview
- Objective
- Introduction
- - Properties
- - Applications
- Experimental
- - Synthesis
- - Characterization
- Results and Discussion
3Objective
- 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
4AEROGEL 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!
5Physical Properties
- Rigid Foam
- Mesoporosity
- Hydrophilic
- Friability
- Low density
- Air is 1.2 mg/cm3
- Record-aerogel is 1.9 mg/cm3
6Thermal 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.
7TransparencyAerogels color is due to Rayleigh
scattering of the shorter wavelengths of visible
light by the nanosized dendritic structure.
8Stardust
9AEROGEL 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
11Chemicals used in synthesis
TEOS (Tetraethoxysilane)
Aluminium Trichloride Hexahydrate
Propylene Oxide
Water
Ethanol
12Formulations
- 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.
13SOL - 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
15Supercritical Fluid Extractor
Level Three - (fits 4 gels)
Level Two (fits 6-10 gels)
Level One (fits 6-10 gels)
16Supercritical 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.
17Aerogel Structure
183D Statistical Modeling of Data
19Shrinkage 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)
20Shrinkage 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.
21FESEM(Field Emission Scanning Electron
Microscope)
22Imaging Aerogel on Nanoscale
23Morphology variation with Al/Si Ratio
- High Al2O3 High SiO2
- 10 81 41 3 1 11
24Aerogel Composites
25SiC Nanofibers
26Al2O3 Electrospunfibers (Calcined to 700C)
27Al2O3 Electrospunfibers (Calcined to 1050C)
28Thermogravimetric Analysis (TGA)
Differential Thermal Analysis (DTA)
- Samples retain 63 - 70 of their original
weight - Crystallization occurs in a range from 980C to
1320C
29Characterizations 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
30Results 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
31Thank 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
32Thank you !
Any Questions?