A few questions about carbon balls. I know nothing about Chemistry.
Is there any theoretical limit to the size of a spherical fullerene? Could they be made the size of a pinhead? A marble? A golf ball? A soccer ball?
Could a large one be made enclosing a vacuum, and lighter than the equivalent volume of air?
Could you fill a balloon or airship with such things and provide sufficient lift to fly?
I’m sure it’s impossible with current technology, but could it ever be possible?
At the larger scale, it’s a ball made from graphene - because the bigger it goes, the flatter the surface becomes.
Buckyballs are ‘perfect’ in that the geometry of the carbon lattice bonds tesselate so as to make a sphere-like shape possible.
There probably are possible geometries for larger structures, but they would not be rigid enough to contain vacuum - graphene is pretty flexible.
I think someone did some maths in another thread to demonstrate that there is no known or theorised material that is both light and rigid enough to contain a vacuum sufficient to provide buoyancy in a standard sea-level pressure environment.
A macroscopic ball of fullerine would collapse if it contained vacuum. Graphene is strong, but also floppy.
There are schemes to create hollow structures out of carbon allotropes that can contain enough vacuum to float in air, but they include internal struts and supports made from diamond-like materials - making them a lot heavier. Add in all this extra weight and the lift available decreases until it is hardly worth doing; they would also be very complex structures and difficult to make. Something like a sealed aerogel with no air inside. It is a lot easier to use hydrogen or helium for lift.
OP asked for spherical fullerenes, but are any of the isolated higher fullerenes even spherical? C70 certainly is not. IIRC it has D[sub]5h[/sub] symmetry.
THanks for thew replies.
So, you can’t make a lighter than air buckeyball. Fair enough.
What if you made a pea-sized carbon ball and filled it with hydrogen? Would that float?
If you filled an airship with these balls, could it fly?
Would such a thing be any safer than the Hindenburg? If hydrogen inside a pea can’t directly touch oxygen outside the pea, would that prevent an explosion?
I know that carbon burns, but less readily than hydrogen. A single spark wouldn’t combust the pea’s skin… or would it?
ETA: to answer Ruken’s point, it doesn’t have to be literally spherical, just a hollow space.
[THREAD=459843]Can we make a floating metal ball?[/THREAD]
Pure allotropic carbon is essentially incombustible and has good high temperature structural properties, hence why it is used as thermal protection for reentry vehicle nose cones, ablative heat shields (PICA-X), and the reinforced carbon-carbon (RCC) leading edges on the Space Transportation System (STS “Shuttle”) Orbiter Vehicle wings.
Fullerenes, however, are not impermeable to smaller molecules and especially not to hydrogen atoms. They do not form some kind of a solid structure but are merely a sort of ‘cage’ formed by covalent bonds between the carbon atoms that small single atoms, and especially hydrogen or helium, could easily slip through, so you can’t simply fill them with light gas or evacuate them. (In fullerenes each carbon is attached to three other carbon atoms which means that one of the bonds has to be a double bond, which dictates the configuration of stable fullerene structures.) In any case, fullerenes, which are all carbon molecules are not lighter than air (three carbon atoms have a higher molecular weight than the diatomic oxygen and nitrogen that make up 99% of our sea level atmosphere) and do not have net positive buoyancy in air.
Stranger
Are fullerene tubes - C[sub]60+10n[/sub] - of arbitrary length possible?
That’s basically a capped subset of carbon nanotubes, so yes.
And once you get log enough that the endcaps don’t matter much, you’ve basically got a cylinder of graphene, and you can pretty much have an arbitrary circumference, too.
In the space opera world of Schlock Mercenary they use fullerene matrices to stabilize antimatter - the fullerene is filled with cold anti-protons - electrostatic pressure (negative antiprotons repelling the electrons of the fullerene bonds) inflates the fullerene and prevents the anti-protons from interacting with the surrounding matter.
Add some oxidizer and energy to disrupt the carbon shell and you get a very energetic “boom”.
Of course, the author is utilizing a great deal of handwavium to make this work …
Handwavium being one of the post-trans-uranic elements, I presume?
I believe the series name is pulloutof-uranic elements.
I want to draw more attention to this. Aerogels are already here. A bunch of small helium or hydrogen filled aerogel bricks wrapped with enough cellophane to keep the gas in, but not enough to totally negate the buoyancy. Put a lot of them together and you have a very damage resistant, gracefully degrading flying platform. Though you may need to get in line, everyone and their mother is trying to get in on aerogels right now and even a little pile of lint sized aerogel balls is somewhat pricey.
My suspicion is that any aerogel capable of retaining He is going to be sufficiently dense that it will negate the buoyancy of the included He.
Any cellophane wrapper will just end up as a Helium balloon with some aerogel in it as well (if the cellophane can even retain He.
Yeah, I’m not following Cornelius Tuggerson’s model. On one hand, today you can easily and cheaply obtain a helium balloon – a (let’s say) cellophane membrane surrounding some helium. Now you want to replace some of the helium with heavier-than-air aerogel, so it’s more expensive and less buoyant. What’s the advantage? The damage resistance comes from that fact that, if I’m understanding you, you have a lot of helium balloons glommed together so you can lose one or a few and keep flying. The aerogel doesn’t add anything except cost and weight.
They are mulling it over for Mars.
Mars has much lower atmospheric pressure (<0.1 psi) so buckling is vastly reduced, and you can see from the section diagram that this isn’t a single shell but a reinforced inner and outer hull with a lattice stiffening it, akin to honeycomb panels frequently used for lightweight structure in aerospace applications. From the paper:
A vacuum airship made of a homogenous material cannot withstand the atmospheric pressure on Earth for any material humans have yet discovered, which can be proven using the critical buckling load of a sphere.
Stranger
You’re right. I was thinking the fact that aerogel is pretty sturdy would allow us to fly around on top of platforms made out of many bricks of it, which seemed cool. However the total lift would be less than a balloon that size that you flew underneath of in the traditional manner. Funky, novel materials make it hard to think realistically sometimes.