Re: Best choice of FTL fuel?

On Jul 28, 11:13 am, Bernard Peek <b...@xxxxxxxxxx> wrote:
In message
<135ce0f8-a24f-41a2-91e5-4d334ebaf...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
WizWom <wiz...@xxxxxxxxx> writes

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.

Graham's Law controls the rate of mixing between two gases, not of the
diffusion through metals of ultra-light gasses. Metals, thankfully,
are impermeable to most gases, which is why you can store, or
instance, Propane in a steel bottle.

He does not form molecules, H2 does. That's why He (mass 4) goes
through metal faster than H2 (mass 2). The Helium actually slips
between the atoms in the crystals of Iron. The Hydrogen Molecule does
not, unless it hits at just the right angle.

It's not about chemical affinity; that would be absorption into the
material, forming chemical compounds with it. That is a source of
loss of the stored gas and usually causes embrittlement of the
container, but it's not significant.
.