[ARC5] Silver refurbishment
Richard Knoppow
1oldlens1 at ix.netcom.com
Thu Dec 24 18:54:26 EST 2020
FWIW, I tested Deoxit-5 for conductive residue. I used an
unused Bakelite terminal strip. I measured the leakage of the
path between terminals in two ways: one was a General Radio
Megohm meter, the other was the ohm meter function of a
Hewlett-Packard 410B. Both measure very high values of resistance
but the GR meter does it with 600 volts applied while the 410B
does it with some very small voltage.
I got the same results with both; no leakage after treating
with the Deoxit. I measured before and after treatment. The
measured resistance was very low and remained the same. The
conclusion is that Deoxit does not leave a conductive residue.
As far as ceramic insulators go, if this is not glazed
insulation it might absorb something from the silver residue. I
did not have any samples to test but my thought is that the
surfaces should be rinsed off thoroughly soon after treatment
since anything absorbed might be bound to the grain of the
insulation.
Also, to be clear, silver oxidizes with great difficulty. The
material found on silver plated surfaces is nearly always silver
sulfide, a poor conductor. Silver oxide _is_ formed in
photographic emulsions by the action of peroxides in the
atmosphere but the conditions there are special and unlike those
applying to surfaces like plated coils or contacts. Ironically,
the main way to prevent the silver in photographs from becoming
oxidized is to treat them to form silver sulfide. Silver sulfide
is extremely stable and a small amount prevents further sulfiding
or oxidation. Its too bad its a lousy conductor.
Two methods of cleaning can be found on the web. The first is
an electrolytic method using aluminum foil and baking soda. The
silver object is immersed in a solution of baking soda in hot
water with a sheet of aluminum foil. The aluminum will absorb the
sulfur from the silver.
Another method is to use a reducing agent such as oxalic acid
or phosphoric acid, which will combine with the silver sulfide
and leave behind metallic silver. Both are primary ingredients in
several commercial cleaners such as Naval Jelly, Zud and
Barkeeper's Friend. Both of the latter are rather abrasive. I
think Tarn-X also uses one of these acids but have not looked it
up. Also (by memory) citric acid is a reducing agent and is found
in lemon juice. Lemon juice and salt make a good cleaner.
My experience is that Tarn-X and Naval Jelly are too powerful
and tend to remove some metallic silver from plated surfaces.
If any are used they should be rinsed off.
I have not seen any comments about using the electrolytic
method on switches but it works like a charm on silver plated
connectors.
On 12/24/2020 7:46 AM, Dennis Monticelli wrote:
> I would like to reiterate that regardless of what chemical you
> use it's important to not allow the dissolved silver to soak
> into the ceramic substrate material, particularly if you're
> dealing with close-spaced wafer switch contacts. If that
> happens , rinse it out. Alcohol is one way to do it. Flooding
> the area with DeOxit D5 is another way. If the part can be
> removed you can use soap, a toothbrush and lots of water.
>
> Bottom line is not to leave conductive paths.
>
> Dennis AE6C
>
> On Thu, Dec 24, 2020 at 7:07 AM Glenn Little WB4UIV
> <glennmaillist at bellsouth.net
> <mailto:glennmaillist at bellsouth.net>> wrote:
>
> If anyone is interested, I have an interesting, but clearly
> off topic,
> story about silver sulfide and electronics.
>
> 73
> Glenn
> WB4UIV
>
> On 12/23/2020 10:58 PM, Richard Knoppow wrote:
> > The problem is that its not silver oxide, its silver
> sulfide, which is
> > a very poor conductor. There are various substances which
> will either
> > remove it but you will be removing some metal too. Any
> silver polish
> > will do the trick but its best to start with something mild.
> >
> > On 12/23/2020 6:12 PM, Brooke Clarke via ARC5 wrote:
> >> Hi Ken:
> >>
> >> It's my understanding that Silver oxide is an excellent
> conductor, so
> >> other than cleaning there's not much to do.
> >> --
> >> Have Fun,
> >>
> >> Brooke Clarke
> >> https://www.PRC68.com <https://www.PRC68.com>
> >> http://www.end2partygovernment.com/2012Issues.html
> <http://www.end2partygovernment.com/2012Issues.html>
> >> axioms:
> >> 1. The extent to which you can fix or improve something
> will be
> >> limited by how well you understand how it works.
> >> 2. Everybody, with no exceptions, holds false beliefs.
> >> -------- Original Message --------
> >>> Dave Stinson at one time suggested using some product
> to clean and
> >>> refurbish the silver
> >>> coils in our transmitters.
> >>>
> >>> I believe he also mentioned refurbishing the silver on
> switch wafers
> >>> and contacts....or
> >>> someone here did anyway.
> >>>
> >>> So what did you use to remove the black oxididation
> from such
> >>> surfaces without damaging
> >>> them?
> >>>
> >>> I have to clean some old bandswitches which are
> oxidized. I will
> >>> have to use Q-tips and some
> >>> care to do this, but I need the "stuff" mentioned here.
> >>>
> >>> Ken W7EKB
> >>>
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> --
> -----------------------------------------------------------------------
> Glenn Little ARRL Technical Specialist
> QCWA LM 28417
> Amateur Callsign: WB4UIV wb4uiv at arrl.net
> <mailto:wb4uiv at arrl.net> AMSAT LM 2178
> QTH: Goose Creek, SC USA (EM92xx) USSVI LM NRA LM SBE
> ARRL TAPR
> "It is not the class of license that the Amateur holds but
> the class
> of the Amateur that holds the license"
>
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--
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL
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