Re: Best choice of FTL fuel?

In message <135ce0f8-a24f-41a2-91e5-4d334ebaf3c7@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>, WizWom <wizwom@xxxxxxxxx> writes
On Jul 26, 1:43 pm, Luke Campbell <lwc...@xxxxxxxxx> wrote:
On Jul 26, 10:59 am, phoe...@xxxxxxx (Damien Sullivan) wrote:

> Peter Knutsen <pe...@xxxxxxxxxxxxxxxx> wrote:
> >And what about molecule size? I have the impression that hydrogen
> >molecules are somewhat of an escape artist, so helium should be worse.
> >Or is that only when it is stored in gas state?

> Why would you think helium would be worse? Hydrogen molecules are
> escape artists because they're tiny and low mass. A helium atom is
> twice the mass of a hydrogen *molecule*, though I'm not sure about size.

The "size" will be slightly smaller. Both electrons occupy the 1s
orbitals, which will be smaller than in hydrogen because of the
tighter binding energy of the +2 charged nucleus. Also, there's only
one of them per molecule. There's also the issue that the
polarizability should be lower than with H_2, so the helium will be
less likely to get stuck on container molecules, making it easier for
it to diffuse out through rubber or wax seals and the like.

As far a it goes, H2 diffuses faster than He; but He goes through
metals faster than H2.
If you want something easier to get, Ammonia (NH3) is much more
stable, liquid at convenient temperatures, and you can just vent the
Nitrogen later.

Hydrogen and Helium diffuse at about the same speed through pretty much any barrier unless there's a chemical affinity between the metal and hydrogen, as there might be for palladium filters. The rate of diffusion is inversely proportional to the mass of the molecule, by Graham's Law. It's counter-intuitive but the size of the molecule does not have a significant effect on diffusion rates.


--
Bernard Peek
London, UK. DBA, Manager, Trainer & Author.

.

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