Lux, Jim via time-nuts writes:

What kind of hydrogen concentration are we talking about ?

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Never attribute to malice what can adequately be explained by incompetence.

FWIW, hydrogen is a bigger molecule (2 atoms) than helium (1 atom, 1
molecule). That's why helium is used for leak testing. If helium won't
leak, neither will anything else.

Steve Hendrix

On 2022-12-08 04:28 PM, Lux, Jim via time-nuts wrote:

On 12/12/22 7:09 AM, Poul-Henning Kamp wrote:

Unknown - I'm looking at "if you've got a cubesat mounted on a big
rocket that uses LH2, and they go through various and sundry tanking and
detanking exercises, what might happen"   In the long term sense,
probably not a high concentration, but I could see there being times
(hours?) when there's a very high concentration.  I mean, they have
those brooms to probe for hydrogen flames for a reason.

There are cases where people think that a sensor was "poisoned" by He
(but never confirmed) because it was stored in a He-rich (but no where
near pure He) environment.  ISS has this problem - the atmosphere is
fairly rich in He, because they backfill the supply ships with He, so
when they open the hatch, a big blob of He moves into the station. (why
they don't use N2, I have no idea.. Maybe they are using He sniffers
after bolting the hatches or something)

Hi

Depends a lot on what you call a “hermetic TCXO”.

There are a lot of parts out there that have sealed crystals inside a sealed TCXO package.
The TCXO package might be resistance welded, it could be solder sealed, it might be glued
shut. The crystal likely is resistance welded or cold welded in a separate enclosure inside
the TCXO package. The TCXO package likely has an inert gas in it at around 1 atmosphere.

There are other parts that have an open blank inside a single package. The package probably
is welded shut, but these days … who can be 100% sure of anything :)

On top of this, a sealed crystal might be in a vacuum or it could be in some sort of inert gas ( often
at pretty low pressure). The same is true of OCXO crystals. The single package unit could
be evacuated or backfilled, possibly at a fairly high ( = close to an atmosphere) sort of pressure.

So lots of variables.

Worst case is a vacuum packaged high Q crystal. It gets gas instead of vacuum and the Q
goes down. If it goes down enough, the oscillator quits. Not a really high probability in a TCXO.
There are parts out there though.  If the crystal is inside it’s package and that’s inside a second
hermetic package, it’s going to take a long time for your hydrogen to get to the crystal ….

Bob

Lux, Jim writes:

Hydrogen can diffuse through any metal[1], because by and large,
metals are just nuclei in hydrogen-soup, but it takes work to do.

If the TCXO is not evacuated, I would not worry at all, because without
a pressure differential the diffusion rates nearly nothing.

If the TCXO is evacuated, and the hydrogen is present for long periods
of time, perhaps because it cannot escape from some badly ventilated
cavity, then you might see detectable diffusion, but I still cannot
imagine it having any relevant effect.

Have you checked NASA literature ?

They must have considered this for Apollo ?

Poul-Henning

[1] Really pure hydrogen is produced by pushing it through a sheet
of Palladium, which is why Fleishmann and Pons were in that business
to begin with.

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Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
phk@FreeBSD.ORG        | TCP/IP since RFC 956
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Never attribute to malice what can adequately be explained by incompetence.

This is true and was proven by experimentation. But I believe it was a
Helium atmosphere not Hydrogen. The He poisoned the MEMS oscillator in both
phones and watches. Fault time was about 30 minutes recovery time was about
3 days. Concentrations were small enough that and employee filling party
balloons at a store had a dead I phone for a while.

Eric

-----Original Message-----
From: Poul-Henning Kamp via time-nuts time-nuts@lists.febo.com
Sent: Monday, December 12, 2022 10:10 AM
To: Discussion of precise time and frequency measurement
time-nuts@lists.febo.com
Cc: Poul-Henning Kamp phk@phk.freebsd.dk
Subject: [time-nuts] Re: hydrogen rich environment and oscillators

Lux, Jim via time-nuts writes:

What kind of hydrogen concentration are we talking about ?

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Poul-Henning Kamp      | UNIX since Zilog Zeus 3.20
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On 12/12/22 11:21 AM, Zen via time-nuts wrote:

Yes, but H2, while a bit bigger than He, is still pretty diffusable (if
that's the right word).

And, I believe the iPhone event was a very tiny MEMS resonator in a vacuum.

I've been poking through the literature and reports, but it does not
appear to be a "well studied problem".

The challenge is that with Cubesats and the like making more use of COTS
components and techniques, there's not a lot of history to go back to. 
Space qualified parts get leak tested with He, etc. so their hermeticity
is generally good.  The same is not necessarily true of other devices.

Look for Knutdsen effect:
Knudsen diffusion, or Knudsen flux, occurs when the mean pore diameter
of the porous medium is smaller than the mean free path of the gas
particles. This type of diffusion occurs in low permeability porous
media, which have small pore radii, and at low gas pressures, when the
mean free path becomes large.
73
KJ6UHN

On 12/12/2022 2:09 PM, Lux, Jim via time-nuts wrote:

On 12/12/22 2:43 PM, Alex Pummer via time-nuts wrote:

This would be at atmospheric pressure, so MFP is on the order of 60 nm. 
I suspect that the pores in metal or silica or whatever are much smaller
than that.