2. Contents
1. About Aerogel
2. History
3. Preparation of Aerogel
4. General Applications of Aerogel
5. Future of Aerogel
6. Conclusion
7. Refrences
3. About Aerogel
• Aerogel is a nanoporous material first synthesized by Dr. samuel
stephens kistler in 1931.
• Aerogels are the world’s lightest solid materials composed of up to
99.98% air by volume.
4. What is Aerogel ?
• An aerogel is solid with air pockets dispersed throughout. Aerogels
are essentially the solid framework of a gel isolated from the gel’s
liquid medium. Some aerogels, such as carbon aerogels and iron
aerogels, are derived from other types of aerogels, but the aerogels
they’re derived from came from a gel directly.
• Nanostructured
• Open porous
5. What is Gel ?
• A Gel is a collidial system in which a nano-structured network of
inter-connected particles spams the volume of a liquid medium.
Gels have some properties like liquids, such as density & some
properties like solids, such as a fixed shape.
• Types of gels
Hydrogels (aquagels) - water is a solvent
alcogels – alcohol is a solvent
xerogels – conventionaly dried wet gels – aerogels.
6. Aerogel is nanotechnology
• A nm is 1 billionth of a meter.
• A hair is 80,000 nm wide.
• Aerogel is a glass foam with
bubbles 10 nm wide.
Scanning electron microscope
picture of aerogel(Photo: Mohan Edirisinghe, University
College, London and Paolo Colombo. Used by permission)
7. Aerogel - Universal solution
• Aerogel is often called a "frozen
smoke”. It consists of lightweight
silica solids derived from a gel,
• Liquid phase is completely
replaced by gas,
• Conduction through the solid is
therefore very low,
• The world’s lowest density solid,
• Aerogel consists of 99.8% of air ,
• Aerogel can be used at
temperatures ranging from - 200°C
to 650°C.
8. History
• In the decade following their discovery in 1929, Samuel Stephens
Kistler produced many different types of aerogels, including
transparent silica aerogels with densities as low as 0.030 g cm-3,
alumina aerogels, tungsten oxide aerogels, iron oxide aerogels, and
tin oxide aerogels
• The 1980′s brought forth safer techniques for producing aerogels,
ways of making aerogels 30 times lighter than had ever been
accomplished before, and a new class of organic and carbon
aerogels that would demonstrate aerogels of different substances
could do amazing and very different things.
9. • In 1990’s The Aerojet corp. in sacramento california began a
cooperative project with Berkeley lab , LLNL & others to
commercialize aerogels using the carbon dioxide substitution
process in 1994. Aerojet obtained the 300 l autoclave formerly
operated by Thermalux & produced various forms of silica ,
resorcinol-formaldehyde, carbon Aerogels. However this program
was abandoned in 1996.
12. Sol-gel process
• The sol-gel process is the preparation of wet-gel, regardless of
whether the precursors are inorganic salts or metal alkoxides. The
main steps in this process are as follows: the precursors dissolve in
solvents (water or organic solvents) to form a uniform solution and
hydrolyze or alcoholyze; then condensation usually occurs to form
sol particles with size of ca. 1-10.0 nm and is gradually transformed
to a gel; and finally the aerogels are obtained through evaporation
or drying.
• The basic 3 principles are as follows:
13. Sol-Gel Science
• Gelification
• Aging
• Soaking/Drying
Mix the reactives(Adjust reaction conditions to control surface area, density,porosity, and
pore size)
Sol (Adjust
viscosity to
prepare thin
films
and fibers)
Gel
Gel Aerogel
Hydrolysis and Condesation
reactions take place
Gelification
Aging Drying
14. Solvation
• The metal cations attract water molecules to form a solvent-unit
( Z is the valence number of M ions) and strongly trend to
release the H+ cations in order to maintain its coordination number:
15. Hydrolysis/ Gelification
• The non-ionizing molecular precursors such as metal alkoxides
(n is the valence of metal M) reacted with water:
SiOR
OR
OR
OR
OH2+ ROH+SiOH
OR
OR
OR
16. Condensation/Aging
• (3 hr at 50 deg. Celsius)
• Dehydration condensation:
• Dealcohol reaction:
+ + ROHSiOR
OR
OR
OR
Si
O
Si
OR OR
OR OR
OR OR
SiOH
OR
OR
OR
+ OH2Si
OR
OR
OH
OR
SiOH
OR
OR
OR
+ Si
O
Si
OR OR
OR OR
OR OR
17. Methods of drying of gels
• Conventional: xerogel
• Supercritical drying Extraction with supercritical CO2 :Aerogel
• Freeze drying: cryogels
•
• Silica xerogel prepared from sodium
silicate by ambient pressure drying
process
• Drying at room temperature for 24 hr.
18. Difference b/w Aerogel, Xerogel &
Cryogel
• An aerogel is obtained when the liquid phase of a gel is replaced by
a gas in such a way that its solid network is retained, with only a
slight or no shrinkage in the gel. It was firstly achieved under
supercritical conditions but it is now possible under ambient drying
conditions as well.
Shrinkage < 15%.
• A Xerogel is obtained when the liquid phase of a gel is removed by
evaporation. It may retain its original shape, but often cracks due to
the extreme shrinkage that is experienced while being dried.
Shrinkage >90%. Therefore the method of drying will dictate
whether an aerogel or xerogel will be formed.
• Cryogel is a commercialized-name for a product developed by
Aspen Aerogels. It is flexible aerogel composite blanket designed for
insulating cold temperature environments ranging from cryogenic
to ambient.
19. General Applications of Aerogel
• Used as an adsorbents.
• Used in a solar cells.
• Now US navy is avaluating Aerogel undergarments as passive
thermal protecton for divers.
• In aircraft de-icing, a new proposal uses a carbon nanotube Aerogel.
The amount of material needed to cover the wings of jumbo jet
weigh 80gm.
• Carbon aerogels are used in the construction of small
electrochemical double layer supercapacitors. Due to the high
surface area of the aerogel.
• In water purification, chalcogels have shown promise in absorbing
the heavy metal pollutants mercury, lead, and cadmium from water.
20. • Insulation of windows and
sections of the roof
• Georgia Institute of
Technology’s (2007) solar
Decathlon House Project used
an aerogel is an insulator in
the semi transparent roof.
• Nasa used Aerogel for Thermal
Insulation of the “ Mars Rover
& Space Suit “
21. Applications of Xerogels:
• Optical Xerogel Sensors
• Electrochemical Xerogel Sensors
• Sensor Biofouling
• Optical coatings and anti-reflective films
• Filter and absorption media
• Space
Space suits,
Anti-sloshing in tanks,
Cryogenic tank insulation.
• electronic components,
capacitors, humidity sensors, batteries, fuel cell, soft magnets,
Geiger counter, IR detector
22. Applications of Cyrogels:
• Sub-ambient piping and equipment,
• Cryogenic storage,
• Sea transport,
• Industrial gases,
• Liquefied natural gas (LNG) import/export pipelines,
• Chilled water systems,
• Gloves, jackets, sleeping bags, boots.
23. Future Of Aerogels
• Today significant efforts are underway to further mechanically
strong aerogels, aerogels of new compositions for sensors and
energy production, and to apply aerogels for use as hydrogen
storage media. Metal aerogels are just around the corner. More
advanced supercapacitors that rival today’s batteries are becoming
likely. Hydrogen production using cleverly-engineered
semiconductor aerogels will change the way we think about energy
and fuel. Smart materials made possible by the unique
combinations of materials properties exhibited by aerogels will
enhance and impact our daily lives.
• Dr. Debra Rolison at the Naval Research Laboratory calls aerogel
“the original nanotech”. But aerogels have come a long way since
the days of Kistler, and there are endless possible applications of
aerogel materials.
24. Conclusions
• Aerogels containing a large number of pores with a typical size of 1-
100 nm are nanostructured porous materials and have shown
unique properties in mechanics, acoustics, thermal, optical, and
other aspects.
• In particular, the aerogels demonstrate extensive applications for
environmental purposes.
• Significantly different from the micron-/millimeter-porous
materials, the aerogels have very low thermal conductivity because
of their nanopores. For example, the thermal conductivity of silica.
• Aerogels is lower than that of the corresponding glassy material
with low 2/3 orders of magnitude, because the fine network
structures of aerogels effectively limit the spread of the local
thermal excitation.
25. • Nanopores inhibit the heat conduction of the gas molecules.
• The light and sound scattering of aerogels are much smaller than
those of traditional porous materials.
• These unique properties not only attract much attention in basic
research, but also have a wide range of applications in many areas.
