[ExI] Aerographite

Anders Sandberg anders at aleph.se
Thu Jul 26 20:19:15 UTC 2012

On 26/07/2012 17:34, Rafal Smigrodzki wrote:
> 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?

I think you have a problem. To quote from Wikipedia:

> Pressure vessels are held together against the gas pressure due to 
> tensile forces within the walls of the container. The normal (tensile) 
> stress <https://en.wikipedia.org/wiki/Stress_%28mechanics%29> 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.^[5] <https://en.wikipedia.org/wiki/Pressure_vessel#cite_note-4> 
> 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.

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.

Anders Sandberg,
Future of Humanity Institute
Oxford Martin School
Faculty of Philosophy
Oxford University

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