[ExI] Aerographite

[Rafal Smigrodzki]

On Thu, Jul 26, 2012 at 2:32 PM, spike <spike66 at att.net> wrote:
>
>>...If you made a sphere of aerographite, covered with a gas non-permeable
> membrane, for example a few layers of graphene, and partially evacuated the
> inside, would it float in the air without being crushed by its pressure?
>
>>...See here, aerographite weighs about 0.3 g per liter, and is pretty
> stiff:
>
>>...http://nextbigfuture.com/2012/07/aerographite-is-lightest-material.html#
> more
>
>>...Rafal
>
>
> I can think of uses for it, but not this one.  You would be better off
> filling your coated aerographite sphere with methane, which is cheap and
> about half the density of air.  Helium is better but more expensive, and
> hydrogen is better still, but more expensive than methane.  Heated air is
> another possibility.  I would consider a large pressure differential as a
> hopeless engineering path, even if we get a really good new material.
>
> In the article, that graph of various materials' specific strength is a
> little misleading.  Note the vertical axis is E/(rho)^2, which makes you
> think it is better than everything.  I would argue it is about the same as
> balsa wood in the parameter that really counts, but it isn't nearly as
> strong as balsa wood by volume, so you need a lot more volume, which brings
> it to a similar weight to a comparable balsa structure.  Of course, if we
> have a new material which can be formed in any shape, and still have
> balsa-ish mechanical properties, that would be cool.

### Think about this - a 10 km high column of aerographite, perhaps
filled with methane, might be neutrally buoyant in Earth's
atmosphere.... does this suggest something?

Imagine building the space rail launcher with this stuff - the pillars
might need to be ridiculously thick but thanks to neutral average
buoyancy in most the atmosphere, you could build very tall structures
with almost no pressure on the foundations, and reaching well into
space.

Rafal