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<div class="moz-cite-prefix">On 26/07/2012 17:34, Rafal Smigrodzki
wrote:<br>
</div>
<blockquote
cite="mid:CAAc1gFjOjUGBmUOvUyihAE2eAZSE3Ve7X9v3PUX0Dq9_8_vabA@mail.gmail.com"
type="cite">
<pre wrap="">A question for the mathematically proficient people: 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?
</pre>
</blockquote>
<br>
I think you have a problem. To quote from Wikipedia:<br>
<br>
<blockquote type="cite">Pressure vessels are held together against
the gas pressure due to tensile forces within the walls of the
container. The normal (tensile) <a
href="https://en.wikipedia.org/wiki/Stress_%28mechanics%29"
title="Stress (mechanics)">stress</a> in the walls of the
container is proportional to the pressure and radius of the vessel
and inversely proportional to the thickness of the walls.<sup
id="cite_ref-4" class="reference"><a
href="https://en.wikipedia.org/wiki/Pressure_vessel#cite_note-4"><span>[</span>5<span>]</span></a></sup>
Therefore pressure vessels are designed to have a thickness
proportional to the radius of tank and the pressure of the tank
and inversely proportional to the maximum allowed normal stress of
the particular material used in the walls of the container.</blockquote>
<br>
So an ultra-thin balloon needs to be ultra-stiff. 1 TPa stiffness is
not really that useful when your balloon thickness is around
0.335 nm. Of course, given the lower pressure inside what we are
looking for is not really the tensile stress but compression stress.<br>
<br>
<br>
<pre class="moz-signature" cols="72">--
Anders Sandberg,
Future of Humanity Institute
Oxford Martin School
Faculty of Philosophy
Oxford University </pre>
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