Another Fullerene Wonder Material?

Another form of fullerene material has been developed:

http://www.sciencedaily.com/releases...1022105021.htm

Could graphene sheet-reinforced composites be stronger than
nanotube-reinforced ones? The graphene sheets would have greater
exposed surface area for more Van der Waals attraction with a
surrounding material matrix or with other sheets. This would reduce
shear slippage as compared to a nanotube, as well as reducing the
number of degrees of freedom for slippage.

What is the tensile strength of a graphene sheet compared to a
nanotube?

What about making a giant balloon or lighter-than-air ship from this
material? Wouldn't you have unprecedented strength-to-weight ratio for
this application?

What about as a planar electrode material for fuel cells? Or what
about as an electrolyte membrane (proton exchange membrane), if you
perforate it with a laser to make lots of small holes for the
hydrogens to pass through?

Would this thing be better to make the space elevator ribbon with than
nanotubes? Perhaps you could make the ribbon using less polymer
filler, if you used graphene sheets for reinforcement, than if you
used nanotubes.

Perhaps the graphene sheets could be used to make a truly comfortable
spacesuit? You could have aerogel underneath for better thermal
insulation. But at least astronauts wouldn't look like the Pilsbury
Doughboy.

"sanman" wrote:

http://www.sciencedaily.com/releases...1022105021.htm

What about making a giant balloon or
lighter-than-air ship from this material? Wouldn't
you have unprecedented strength-to-weight ratio
for this application?

It's worth noting that with _sufficient_ strength to
weight, balloons (with ribs) could be filled with
cheap vacuum instead of expensive helium or dangerous
hydrogen, and probably provide greater net lift.

Tim Tyler's recent work in double-trussed geodesic
domes might pertain to such a vehicle's structure.

http://hex.alife.co.uk/domes/index.html

HTH

xanthian.




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Kent Paul Dolan wrote:
[...]
It's worth noting that with _sufficient_ strength to
weight, balloons (with ribs) could be filled with
cheap vacuum instead of expensive helium or dangerous
hydrogen, and probably provide greater net lift.

You could, but it wouldn't gain you much.

Air has an average molecular weight of about 30. Hydrogen has a molecular
weight of 2. Lifting capability is (mass of displaced air) minus (mass of
gas replacing air); so hydrogen would give a lifting capability of 28. All
vacuum could do would be to raise the lifting capability to the theoretical
maximum of 30. a 5% increase.

That increase would almost certainly be soaked up by the added mass of your
envelope, which now has to be rigid to withstand a considerable inward
force. Hydrogen balloons aren't subject to this, because the gas on the
inside is at the same pressure as the gas on the outside, so there's a net
zero force.

Not only that, but using vacuum would introduce some rather unpleasant
failure modes (such as your vehicle imploding violently). You're probably
better off sticking with hydrogen. Helium if you're feeling rich.
(Molecular weight of 4, so a lifting capability of 26 --- not much worse
than hydrogen.)

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| | capitalism, it's just the opposite." --- John
| ) | Kenneth Galbrith
+- www.cowlark.com --+

In sci.space.tech, on Fri, 26 Nov 2004 14:56:30 GMT, David Given sez:
` Kent Paul Dolan wrote:
` [...]
` It's worth noting that with _sufficient_ strength to
` weight, balloons (with ribs) could be filled with
` cheap vacuum instead of expensive helium or dangerous
` hydrogen, and probably provide greater net lift.

` You could, but it wouldn't gain you much.

` Air has an average molecular weight of about 30. Hydrogen has a molecular
` weight of 2. Lifting capability is (mass of displaced air) minus (mass of
` gas replacing air); so hydrogen would give a lifting capability of 28. All
` vacuum could do would be to raise the lifting capability to the theoretical
` maximum of 30. a 5% increase.

` That increase would almost certainly be soaked up by the added mass of your
` envelope, which now has to be rigid to withstand a considerable inward
` force. Hydrogen balloons aren't subject to this, because the gas on the
` inside is at the same pressure as the gas on the outside, so there's a net
` zero force.

` Not only that, but using vacuum would introduce some rather unpleasant
` failure modes (such as your vehicle imploding violently). You're probably
` better off sticking with hydrogen. Helium if you're feeling rich.
` (Molecular weight of 4, so a lifting capability of 26 --- not much worse
` than hydrogen.)

Passive solar heating of lift gas, raising its temperature significantly
above the ambient, could get you a bit more lift, getting the internal
density a bit lower for little or no weight penalty - say a transparent
upper half and black bottom half to the balloon. Perhaps taking a
small weight hit to improve the surface insulation might be a win
above some volume point, as well. But then, all this requires the
gas, and optionally the skin, to expand in size, so you have to either
have more initial slack surface material (which will start out as
dead weight) or else use a such a quantity of lift gas that some
must be jettisoned at altitude.

--
================================================== ========================
Pete Vincent
Disclaimer: all I know I learned from reading Usenet.