To catch particles in space, the Stardust spacecraft
uses a special material called aerogel. These
are frequently asked questions about this material:
How is aerogel made?
Mixing four chemicals, which
react to form a wet gel, similar to a gelatin
dessert creates Aerogel. The gel is then dried
in an autoclave, in essence a pressure cooker
that applies pressure and heat.
What is it used for?
The Stardust Project is using
aerogel as a capture media, where it will collect
very small interstellar and cometary particles
as they embed themselves in the porous aerogel.
Because of its unique physical properties, aerogel
has also been proposed for a wide variety of uses,
including thermal insulation, acoustical insulation,
optical components, catalytic supports and filters.
What does it feel like?
The microstructure of aerogel
is extremely porous, so it feels like volcanic
glass pumice or even a very fine, dry sponge,
except that it is much lighter.
Why is it blue?
Aerogel has a blue cast for
the same reason that the sky is blue. The very
small particles that compose the aerogel scatter
blue light, the same as our atmosphere scatters
blue light. Similarly, when you look through the
aerogel the light appears yellowish or reddish,
like that of a sunrise or sunset.
Where can I get some aerogel?
Aerogel is commercially available
in limited quantities from a few companies. These
can be found quite easily by searching the Internet
using the keyword: aerogel. JPL only produces
specialized aerogel used for spaceflight.
How much does aerogel cost?
Aerogel is relatively expensive
primarily because it is currently made in very
limited quantities. While increasing the scale
of aerogel production will reduce the cost, the
basic process and raw materials are still somewhat
costly. For relatively small quantities of aerogel
the cost is about $1.00 per cubic centimeter for
What makes aerogel so special?
The fact that typical aerogels
are between 95 and 99.5 percent porous gives them
their unusual characteristics. Because of this
highly porous quality they are characterized by
extremely high surface area, high thermal and
acoustical resistivity, low dielectric constant,
and low refractive index. There are other materials
that exhibit each of these properties, however,
only aerogel exhibits all of these properties
at the same time.
Who invented aerogel?
Aerogel was first made in the
1930s by Samuel S. Kistler, who obtained several
patents for making a variety of aerogel, including
silica, alumina, chromia, tin and carbon.
Why is it called a gel?
During the production of aerogel
a wet gel is formed which when dried becomes filled
with air. Thus the name aerogel, which means:
Is it solid?
Aerogel is made up of microscopic
beads or strands connected to form a continuous
network. Since the network fills space and supports
itself, it is considered a solid.
What happens if I touch
Silica aerogel is semi-elastic
because it returns to its original form if slightly
deformed. If further deformed, a dimple will be
created. However, if the elastic limit is exceeded,
it will shatter catastrophically, like glass.
Is aerogel such a good insulator
because the air within is trapped and immobile?
And, is this why it doesn't melt?
Heat is transferred in three
ways: convection, conduction, and radiation. Aerogel
is a good thermal insulator for convective heat
transfer because the air is severely limited in
the distance that it can move and thus transport
heat energy. The pores of a typical 20 mg/cc silica
aerogel are roughly 0.00000001 meters in diameter.
Aerogel is a good conductive insulator because
the silica molecules are not as well "connected"
as those in a metal (a good thermal conductor).
Silica aerogel is a poor radiative insulator because
infrared radiation (which transfers heat) passes
right through silica aerogel. For this reason,
carbon was added to the MER aerogel to stop infrared
radiation from passing through it. This is also
why one feels the heat from a flame. Air is a
poor convective transporter of heat, but infrared
radiation passes right through air, from the flame
to your hand.
Note: the index of refraction
depends on the density of the aerogel.
Would it be possible to create aerogel lighter than air by using
helium instead of air?
Aerogel cannot be made less dense than air by filling it with
helium. You might be able to make it less dense than the
surrounding atmosphere by filling the aerogel with helium and then
placing it in an atmosphere of radon or possibly xenon.
|Last updated September 29, 2005