IRJET- A Review on Aerogel An Introduction

International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056
Volume: 05 Issue: 03 | Mar-2018 www.irjet.net p-ISSN: 2395-0072
© 2018, IRJET | Impact Factor value: 6.171 | ISO 9001:2008 Certified Journal | Page 4098
A Review on Aerogel An Introduction
Ghodake Sagar S.1, Londhe Babasaheb C.2
1Department of Mechanical Engineering,S.N.D.COE &RC,Maharastra,India
2 Asso.Prof.,Department of Mechanical Engineering,S.N.D.COE &RC,Maharastra,India
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Abstract – Aerogel is a solid with extremely low density and
low thermal conductivity. Nicknames include frozen smoke,
solid smoke, solid air, or blue smoke owing to its translucent
nature and the way light scatters in the material. It look like
expanded polystyrene to the touch. It can be made from a
variety of chemical compounds. by extracting the liquid
component of a gel through supercritical drying Aerogel is
produced. This liquid can be slowly dried offwithoutchanging
the solid matrix in the gel, as would happen with conventional
evaporation. The first aerogels were producedfromsilicagels..
Aerogel does not have a designated material withsetchemical
formula but the term is used to group all the material with a
certain geometric structure. Aerogel has become a materialof
interest to scientists in recent decades due to its unique
physical properties that give it the potential to improve
technologies in a variety of fields. In particular, aerogels offer
the lowest densities and the lowest thermal conductivities of
any known solid. Since then, many other types ofaerogelshave
been created, including carbon-basedandclay-basedaerogels.
Silica-based aerogels are the simplest and most widelystudied
type of aerogel, with new uses and applications arising ever.
The goal was to create a reliable, non-toxic method, using
inexpensive materials
Key Words: Aerogel, Material, silylating agents, Airglass,
Alcogel
1.INTRODUCTION
In 1931, ‘Steven Kistler’ made a bet with a colleague that he
could prove a wet gel contained a solid matrix the same size
and shape of the gel. To do this he began with a gel and
extracted the liquid, leaving a low-density solid behind.
Using an autoclave to drivethe liquid past itscriticalpointhe
was able to conquer the obstacle of surface tension which
would otherwise rip apart the internal solid structure of the
gel. His successful wager produced the first silica-based
aerogel. For half a century this curious material went
relatively unnoticed, due to the notorious difficulties and
safety issues involved in its creation .
In the early years, fabricating aerogels meant sending
alcohol to volatile pressures and temperaturesinorderforit
to reach its supercritical point and allow for the
supercritical-extraction of the gel. Then, in the 1980’s,
interest was renewed when a French scientist, attemptingto
improve the fabrication processfor the French government,
developed a process which used less-toxic materials. He
switched out methyl alcohol and Tetra Methyl Ortho Silicate
(TMOS) for the safer pairing of ethyl alcohol and Tetra Ethyl
Ortho Silicate (TEOS). The next breakthrough came in the
early 1990’s when liquid carbon dioxide replaced the ethyl
alcohol involved in the gel before the sample was taken
through the supercritical process. This allowed scientists to
bypassthe dangerouspressuresandtemperaturesneededto
send the pure ethanol past its supercritical point. Liquid
carbon dioxide has the relatively mundane requirements of
305 K and 1050 psi to be brought to its supercritical point.
To obtain hydrophobic low density and low thermal
conductivity aerogels for thermal insulation and liquid
marble formation purpose, various sol-gel parameters,
processing parameters namely washing, shaking, various
solvents, silylating agents and drying method were varied
along with doping the gel with TiO2 powder.
Aerogel is a typical nano-porousthermal insulationmaterial
with open-cell structure. Due to the excellent properties,
aerogel is widely applicable in industry fields such as
astronautics, thermal insulation and so on. However, the
extremely low porosity and complicated structure make it a
challenge to accurately predict the effective thermal
conductivity and enhance the insulation performance. The
experimental measurements of the aerogel thermal
conductivity under different pressureandtemperature.Most
of the present researches adopted some regular structureto
represent the aerogel structure, which can simplify the heat
transfer analysis of materials, but also contain artificial
parameters and ignore the stochastic characteristic of
aerogel material. In the aspect of numerical study, used the
macroscopic numerical method to obtain the thermal
conductivity, whereas using traditional numerical methods
is hard to solve the micro-scale heat transfer problem. the
open-cell micro-porous random structure of aerogel was
reconstructed basing on the solid-phase growth principle,
which has no artificial parameters and guarantees the
stochastic characteristic of aerogel material. Then thelattice
Boltzmann method was adopted to predict the aerogel
effective thermal conductivity.
The increase of building energy consumptions driven by the
higher expectations for indoor comfort, together with
concerns for the rise in GHG emissions, are pushing the
research and design interest toward energy saving in
buildings. The development of new insulating materials is
among the most promising options. The aerogels are
considered one of the most promising family of materialsfor
insulating purposes, given their high thermal insulation.
They are dried gels with such a high porosity that they have
lower thermal conductivity than air. Moreover, they are

nontoxic, low flammable, lightweight,andairpermeable.The
synthesis of these materials was discovered in the early
1930s and since that time, several products have been
developed, mainly using silica as a raw material. The
production process of silica aerogel aimsto buildsufficiently
rigid materials with the same porous texture as that of the
wet sol-gel stage. The aging of the gel and its drying are the
two most risky phasesof the production of aerogels, and are
responsible of their high cost. The solid microstructure of
the aerogels has been described as “beads on a string” or
“pearls on a necklace” referring to the roughly spherical
particles connected by small necks or thin strands. This
structure is much lessstiff than that of an open-cellfoam(up
to 30 to 50 times lower ). After cost, the main limitation that
is preventing aerogels from becoming more widely used in
the building sector is hence their high fragility.Theirfragility
has hence suggested the use of aerogels in protected
compartments. Given their good light optical properties,
aerogels have been considered for building fenestration
systems since the 1980s. Products with aerogel in the
interspace between the window panes have shown to
provide high thermal resistance and light transmittance.
Two types of aerogel exist, the monolithic and the granular
aerogels. Monolithic silica aerogels have higher solar
transmittance than granular ones; for example, 10 mm
monolith translucent silica aerogel windows have shown a
solar transmittance up to 0.8, whereas the maximum solar
transmittance of granular silica aerogel windows is around
0.5. However, cracks often occur when manufacturing large
pieces of monolithic aerogels, so glazing systems with
monolithic aerogel have not yet been used beyond research
prototypes . A monolithic aerogel window with vacuum
glazing and a 13.5 mm thick aerogel panel was developed
within the EU project HILIT; this project proved the
possibility to realize windowswith a thermalconductivityof
0.66 W/m2K and a light transmissibility above 0.8. Since
then, Airglass AB, the firm that provided the aerogel in the
HILIT project, has continued refining the productionprocess
of monolithic panels.
1.1 WHAT IS AEROGEL?
Aerogel means an extremely light and porous semi-solid
materials. Silica based aerogelsare among the lightest ones,
can be less than four times as dense dry air , and some are
nearly transparent , itsnick name is‘’solid smoke’’or‘’frozen
smoke.’’
Because of aerogels unique structure, its use as insulator.
the super insulating air pockets with the aerogels structure
almost entirely counterect the three methods of heat
transfer .
PROPERTIES OF AEROGEL
 Low density - UV Infrared
 It has 90 – 99.9 % porosity.
 Large sound absorption - low sound velocity
:Damping > 50 dB, vl ≈ 100 m/s
 Low thermal conductivity: 0.005 - 0.1 W/mK
 It can be Transparent or opaque or can be coloured.
 Variable refractive index (1.001 to 2.1)
 No reaction with metallic melts up to 950°C (Silica
and some other oxide aerogels)
 Hydrophobic by polymeric residues (-CH3)
ACTUAL PHOTOGRAPH OF AEROGEL
Fig 1. Actual Aerogel
1.2 PRODUCTION PROCESS.
Aerogels begin life as a silica (SiO2) gel. Though aerogels
have also been created with alumina, chromia, tin oxide,
carbon and other materials, silica versions are the easiest
and most reliable to produce. The silica gels are about 99%
liquid by weight, but contain matrices that give the liquid
surface tension. In a silica gel these molecular networks are
made up of silica dendrites.
The first step in making aerogelsis to create whatiscalleda
“wet gel.” Currently, the best way to create the wet gels is to
begin with a silicon-alkolyde precursor, such asTEOS,which
was used for this project. The chemical makeup of TEOS is
Si(OCH2CH3)4, which, when added to water, achieves the
chemical reaction.
Si(OCH2CH3)4 (liq.) + 2H2O (liq.) = SiO2 (solid) +
4HOCH2CH3 (liq.)
eq. The amount of water indicated in eq is only enough to
exactly balance the reaction. In practice, anywhere from4to
30 timesmore water should be used to increase thestrength
of the gels. This chemical reaction is generallyaccomplished
in ethanol.
Acid or base catalysts are added to this reaction in order to
decrease gelation time from several days to around an hour.
Base catalysts were used in this project due to their

tendency to create clearer aerogels. Base-catalyzed aerogels
also retain more of their volume throughout processingthan
do their acid-catalyzed counterparts.
The current precursors are largely alkoxides M(OR)n which
are compounds consisting of a metal M and an alkoxide
group OR. With silicon precursorsthe R designatingthealkyl
group is often a methyl CH3 group or an ethyl C2H5 group.
The reason silica-based aerogels have been studied much
more than any other type is because silicon atoms carry a
reduced partial positive charge δ+. In Si(OEt)4 δ+ is about
0.32 .
APPLICATIONS OF AEROGEL
1. Use of carbon black in aerogel-like composite
material with heat insulating properties .
2. Functional starch based carbon aerogels used for
energy applications .
3. Phenolic Aerogel used in improvement of Polyester
Blanket Thermal Insulators properties .
4. Aerogel is used in everything from makeup and
paint to napalm.
ADVANTAGES & LIMITATIONS
 Advantages
1. Aerogel is the best overall type of insulation.
2. Fibreglass is cheap.
3. Mineral wool is effective, but not fire resistant
cellulose is fire resistant and ecofriendly, but hard to
apply.
4. Polyurethane is a good insulation product.
5. Because of their high thermal resistance, insulation
products based on aerogels (e.g. insulation blankets
or granules) achieve a relatively high level of thermal
insulation with a limited insulation thickness. This
makes it possible to save interior space (on walls or
floors).
6. Insulation blankets based on aerogels can be easily
cut to shape and are flexible enough to be fitted
around complicated details. Their main advantage
compared to vacuum insulation panels (VIP) (which
have a thermal conductivity in the same order of
magnitude) is their reduced sensitivity to mechanical
damage.
7. Aerogels are water repellent and vapour open.
 LIMITATIONS
1. Aerogel production cost is high and hence it is can
not be affordable for small scale production.
2. Aerogel is soft and lightweight so has poor
mechanical properties.
3. Aerogel is prepared from Chemicalsso it may affect
Health during production.
4. Aerogel is very soft material so large pieces cannot
be lifted at corners.
5. Silica aerogel is destroyed by contact with liquids.
Fig.2 Product made by aerogel
3. CONCLUSIONS
Thus, from the above paper Aerogel is a material can be
used to replace commonly used solid materials. A semi-solid
Aerogel is currently used in Aerospace application to
reduced the heat transfer rate and simultaneously reduced
heat loss .
ACKNOWLEDGEMENT
Successful completion of work can never be one man’s task.
It requireshard work in right direction. Therearemanywho
have helped to make my experience as a studentarewarding
one.
I express my deep sense of gratitude and indebtedness to
my Head of Department Prof.V.G.Bhamre. and Guide Prof.
B.C.Londhe for their valuable guidance, constant
encouragement and kind cooperation throughouttheperiod
of work.

Many friends have helped me stay sane through this work.
Their support and care helped me overcome setbacks and
stay focused on my work. I greatly value their friendshipand
I deeply appreciate their belief in me.
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Materials & Design 130 (2017) 452–458.
6. Umberto Berardi, “Development of glazing systems
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Physica A 406 (2014) 131–138.
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