[time-nuts] Heated crystal? & Rb tube corrosion (FE-5680A)

Attila Kinali attila at kinali.ch
Thu Dec 1 05:18:54 EST 2011

On Thu, 1 Dec 2011 01:00:44 -0500
"Steve ." <iteration69 at gmail.com> wrote:

> Note the corrosion around the cheaper metal parts (screws, spacers, shell).
> I can't speak for the FE-5680A, but when i see something like this in the
> instruments i maintain it's a tale-tale sign gas mitigation.

I have to agree with Bill that there is no corrosion. At least i dont
see any, but on the head of the Rb cell.

>From the chemistry point,  Rb or the noble gas buffer in the cell will
not corrode any metals if they would leak. Because noble gas are noble
and nearly completely inert (at least at the temperatures we are talking
about) and Rb is less noble than anything else you will find in there,
hence will oxidize first.

There is a very slimm chance that Rb salts (after Rb has been oxidized)
could lead to an acidic reaction. But i can neither prove or disprove
that with my limited chemistry knowledge.

But in this case, it's not Rb or any of its salt that's the culprit.
If you have a look at http://n1.taur.dk/fe5680a-2/IMG_1393.JPG
you see that the corrosion around the Rb tube is at the spot where
two transistors are soldered to the tube. The metal of the transistors
is copper plated with tin and soldered with a tin based solder.
What you'll get here is an sacrifacial anode effect, ie the copper
does oxidize the less noble iron/steal.

Other than that one spot, i have to say that the whole device looks
like new. No dirt, no corrosion where you'd expect it. Even the solder
joints look like new.

Oh yes, if you mean http://n1.taur.dk/fe5680a-2/IMG_1398.JPG looks like
a corroded crystal contact, i have to disapoint you. All you see there
a not so ideal solder joint. Ie the solder wasnt heated well or did take
too long to cool down, which lead to a partial crystalization of the
surface. This then looks a little bit rough and can give the impression
of corrosion if one expects a completely flat and shiny surface.

				Attila Kinali
Why does it take years to find the answers to
the questions one should have asked long ago?

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