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

[Azelio Boriani]

I had a bad experience with chinese sellers: I got a Z3815A with the Furuno
GPS enclosure completely rusted and a LPFRS that I suspect was submerged in
water: rusted and corroded internally tough still working... the seller has
agreed to send another one.

On Thu, Dec 1, 2011 at 11:18 AM, Attila Kinali <attila at kinali.ch> wrote:

> 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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