[Boatanchors] Smart People: Gassy Tubes Reversable?

[J. Forster]

Yes,

Gasses diffuse through glass, even if the metal-glass seals are perfect.

It depends on:

Pressure differential
Glass permeability
Gas molecule size.

If you have a glass Dewar and you leave it exposed to He overnight, it'll
be useless the next day. The He will diffuse through the glass and spoil
the vacuum. HeNe LASERS die for the same reason.

BTW, gasses diffuse through metals too. Hydrogen diffuses through hot
Palladium very well. That's how untra-pure H2 is made.

This same physics is use to enrich uranium, as in Iran.

-John

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> >
> The diffusion rate through a semi-permeable membrane detends on the
> pressure difference across the membrane.
> >
>
> Hi, John. I think you are referring to gas diffusing through the tube
> envelope? I hadn't considered that. I was assuming gas "leaking" in or out
> via wire lead seals, sort of like through nano-cracks between materials.
>
> 73,
> Wayne
> WB4OGM
>
>