Carbon Aero Gel

Is it cheaper than helium by a factor of 1600/1785 ?

I could be wrong,but my understanding was that it was the weight in air,not in a vacuum,so the internal air weight can be disregarded.

But, I could be wrong.

If that's its weight in air, measured on a non-sealed balance pan, then that weight is the mass of the aerogel. The weight of the air around and internal to the aerogel matrix is unrestrained, therefore it exerts a constant pressure on the balance pan that is counteracted by the air pressure underneath the pan.

So the density of the aerogel when calculated dimensionally may be significantly less than the equivalent air density at STP, but that's misleading as the gel is an open matrix. The real density is actually ADDITIONAL to the air mass (or water, vacuum etc.) that fills that matrix.

So it may float away in a breeze, but it will probably sink to the bottom of a container of water if submerged for a long period of time. On the other hand, if the stuff has good compressive strength it would make possible gas free rigid lighter than air craft- exactly the sort of design you see from 300 year old drawings with vacuum spheres!

"I see!" said the blind carpenter as he picked up his hammer and saw.

Actually, would be interesting to see what densities of liquid an aerogel would sink in (eventually of course, it would have to wet into the matrix first).

See note 2 for items 2, 3 and 4

http://en.wikipedia.org/wiki/Density#Various_materials

Imagine enclosing this material in a hot-air balloon envelope, and pulling a vacuum on it,then filling it with hot air. It has great recovery from compression.

With the inherent insulating properties,it would hold heat for a long time.

A certain amount(TBD) of the balloon volume could be reserved, free of the aerogel for altitude adjustment.

This would save a lot of fuel.

Would this work?

Giving up rapid control of the heat, is giving up control of altitude....which is pretty much the only control you have, short of jumping out....

Problem is that air will cool as it expands into the vacuum. Seems to me you'd be much better off with just blowing hot air into it topside and venting the bottom until the desired temperature was reached. Maybe suction would help to get the air flowing through it. I really don't know what the insulation effect would be, other than to reduce convection inside the balloon.

Do you know what the compression of aerogel at 14 psi is??

When I first read this I assumed the pores in the material are evacuated and sealed. In that case the density (total) could in principle be as quoted. I don't know whether that is practical.

If a balloon could be made to take full vacuum but same mass as one filled with hydrogen or helium (which of course it can't) it would have have greater lift than gas-filled.

Well, you are wrong.

Yes, wrong. The true density of the carbon skeleton will be that of carbon. It is arranged in thin rods to enclose a large space and if you compute density as weight for that large space = very low, but as another said, you must count the air in that space - unless it is sealed with a membrane and the rod structure is strong enough to withstand normal air pressure, in which case you would have a lighter than air balloon.

I doubt it will have the strength, but you might be able to create small spheres that are strong enough to serve in that role?

Think of a sponge. If it's dry, it floats in water. If it's soaking wet it sinks. Same thing with aerogel, the air weights it down.

It would likely rise if it were infused with helium, at least until the helium leaked out (probably rapidly). It would be lightest still if it were filled with vacuum, but the air pressure would quickly crush it if air did not leak in.

I understand.It is all about displacement.

The molecular weight of the carbon is heavier than air.

Like a ship that displaces it's weight, if you punch it full of holes it will sink,because the steel is heavier than water.

If you keep the water out, it will float.

Likewise with the air in this case.

If they could make an aerogel from a material lighter than air, it would float in air.

Yes, a solid material, less dense than air, would indeed rise until the external density was a match for it.....sadly, it can not be.

"If it's soaking wet it sinks"

Only if the sponge material has a specific gravity of more than one.

This is why the article talks about this material being balanced on flowers instead of being tethered to a vase of water.