Do-it-yourself aerogel?

[William Beaty <billb@eskimo.com>]

On Mon, 26 Aug 1996, Wolfgang Rueckner wrote:

> The recent communications on Rayleigh scattering (in a fish tank) and the
> picture on page 31 in the August '96 Physics Today reminded me of a large
> cube (about 8 cm on a side) of aerogel that I saw at the Franklin Institute

I wonder how hard it is to synthesize this material.  Months after the
initial announcement of aerogel (LLL, I think?) there was another
announcement.  Someone had discovered that aerogel could be made without
the triple-point fluid technique, via freeze-drying ice cubes of agar.
I've not tried this myself.  By evaporating an agar ice-cube in a vacuum
chamber, the network-crushing gas/fluid interface is avoided.  The product
was to be called "Seagel." I've heard nothing about it since.  I wonder
what happened?  I wonder if there is a trick to it, or if it can be made
with nothing more than a vacuum chamber inside a freezer?

Another interesting event: in 1993 I saw an accidental creation of aerogel
by a welder.  The material was very similar to the silicon aerogel I've
seen, though it was quite a bit more fragile.  Phys-L people might wish to
try reproducing the effect.  A person was welding a zinc-plated electrical
box to a museum exhibit frame.  This is unwise, since zinc evaporates and
the fumes are toxic.  When the small box was opened, it was found to be
full of transparent, blue-white feathery substance.  The stuff behaved
like partially-dry soap suds, but no bubble structure was visible.  The
fragments were a few cm across at most. When viewed against a white
surface the material looked yellow-transparant, when viewed against black
it appeared smoky-blue.  When dropped it fell more slowly than a feather.
It was slightly flexible, but when stretched it fractured.

When the galvanized electrical box was being welded, the flame (or arc?  I
didn't record the type of welder) blew into a screw-hole in the back of
the box.  It is also possible that the high heat of the welding process
evaporated zinc directly from the inner surfaces of the box. I assume the
incandescent flame contained either zinc vapor or molecular zinc oxide,
and when this impinged on the metal surfaces within the box, it cooled
instantly and formed one of those diffusion-limited fractal percolation
structures that arise during deposition processes.  This material is
basically identical with aerogel, though the details of the structure
probably differ at microscopic scales.  Over many weeks the material
shrank and developed a white crust, which suggests that the aerogel was
zinc metal and was slowly being oxidized. 

If you are tempted to mess with zinc vapor, take the standard precautions
necessary when working with toxic materials. 

A final thought: if carbon is substituted for zinc, and if the whole
experiment is performed under inert gas, the result might be carbon
aerogel made from nanotubes and buckyball crystals.  My zinc aerogel was
basically an exotic form of welding soot, and it wouldn't be entirely
unexpected to see aerogel form during carbon soot deposition.  Oxygen
would probably attack it though, in the same way it's said to attack
buckyballs and carbon nanostructures. 

......................uuuu / oo \ uuuu........,.............................
William Beaty  voice:206-781-3320   bbs:206-789-0775    cserv:71241,3623
EE/Programmer/Science exhibit designer        http://www.eskimo.com/~billb/
Seattle, WA 98117  billb@eskimo.com           SCIENCE HOBBYIST web page