Floating Hollow Ball: Defying Balloon-Like Properties

[djsourabh]

Is there any material,when made a hollow ball out of it & filled with lighter gas than air,will rise in air according to archimedes principle? But upon removal of that gas,it should not contract itself in volume like any balloon does...it should be able to retain its volume as it is even if there is a vacuum in it,& surrounded by air.

 

[mfb]

Probably not with a spherical shell, but a different structure could work (together with some very thin foil), see wikipedia.

Alternatively: the lightest aerogels are lighter than air. A solid sphere of that material, with some thin foil around it (to keep air out), could work, I don't know how stiff those aerogels are.

 

[djsourabh]

Probably not with a spherical shell, but a different structure could work (together with some very thin foil), see wikipedia.

Alternatively: the lightest aerogels are lighter than air. A solid sphere of that material, with some thin foil around it (to keep air out), could work, I don't know how stiff those aerogels are.

If an enclosed shell is made,out of aerogel, can it sustain the atmospheric pressure if gas out of that shell is removed/rarefied? Does anybody have any idea about it?

 

[mfb]

A shell out of aerogel? I thought about a solid volume. It would need a bulk modulus at least of the order of 100kPa with a density below the density of air (even after compression).

 

[etudiant]

Air pressure at sea level is about 15 pounds/square inch. This commercially available insulating aerogel http://zeroloft.com/ claims it will lose only 15% of its loft under 15psi pressure.
So the idea is worth looking into further, because it seems possible. Not so sure about the costs.

 

[mfb]

"It is made of 99.8% air" - that does not look lighter than air.

And the page has inconsistent values:
At "technology":
"Density: Currently available in densities from 0.10 to 0.12 g/cm²"

At the front page: "It is chemically identical yet 3,000 times less dense than glass."
So glass has a density of 300g/cm²? Certainly not.

 

[AlephZero]

"It is made of 99.8% air" - that does not look lighter than air.

The "density less than air" numbers are the mass density of aerogel measured in a vacuum.

I think the two facts that (1) 99.8% of the aerogel is "holes", and (2) the buoyancy forces from the surrounding air have a large effect on its weight (as compared with its mass), are enough to explain most of the nonsense and/or misleading information in popular science articles about the it.

It is self-evident that lumps of aerogel (with the "holes" full of air) do not spontaneously float upwards like helium balloons!

I don't know whether its crushing strength would be high enough to make a structure that could withstand an external pressure of 15 psi, with a vacuum inside. I don't think it would make much difference whether or not the actual aerogel material contained air or vacuum.

 

[djsourabh]

ok. thank you everybody.but is it still worth buying the aerogel? for experimentation? I can't exactly conclude.

 

[mfb]

The numbers I found were not promising. A rigid structure, a thin foil and vacuum look like a better approach.