Keras
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Silver plating mixtures
Folks,
I've been trying recently to find out how one can silver plate copper things without using electricity. In other words, to devise a suitable mixture
able to deposit a fair thickness (~ 1 µm) of metallic silver on copper (the ultimate goal is to make higher quality coils for use in RF electronics,
because at several hundreds MHz the skin effect repels all the current towards the surface of the wire).
I've figured out that there needs to be a very slow exchange between copper metal and Ag(I) ions, because dipping copper into a bare solution of
silver nitrate results in an accumulation of silver dust on the copper, but nothing really sticks (reaction is too fast). So I used various
complexants: ammonia, EDTA or sodium thiosulphate to slow it down. The last two seem to work better, but the plating is often irregular, and it seems
that it flakes off when it exceeds a certain thickness. The surface becomes shiny white, then dulls out as more silver accumulates, and brushing it
even with soft tissue results in local peel-off.
Anyways. Does anyone have a formula for a mixture that would deposit a shiny silvery layer of reasonable thickness, or what compound/current intensity
to use for electric plating?
I also read that starting with a thin layer of nickel would allow the silver plating to be much more efficient, because the nickel would not dissolve
into the plating solution?
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Sulaiman
International Hazard
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non plating thoughts ... from memory .. unverified
because silver is a slightly better conductor than copper it has a smaller skin depth at any given frequency,
the benefit of silver is its very thin (c1um) passivating yet moderately conductive oxide layer
- compared to the crud when copper tarnishes.
So, enameled copper is almost as good as silver plated wire.
If you want the bulk of current to be in the silver skin
then 1um is too thin for a few hundred megahertz.
(maybe 6 um ?..I'll leave the math for you to do)
At 100's MHz, proximity effect, self capacitance, and core losses dominate.
CAUTION : Hobby Chemist, not Professional or even Amateur
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Keras
International Hazard
Posts: 1148
Registered: 20-8-2018
Location: (48, 2)
Member Is Offline
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Well, I debated this with Google Gemini once more. It seems that silver plated wire warrants a gain of ~ 6% in the Q factor of a coil, despite,
you’re right, the thinner skin effect. In other words, the thicker skin effet in Cu doesn’t fully make up for reduced conductivity w/r to silver.
Skin effet depth in silver at 500 MHz is about 3 µm.
Apparently, dielectric losses in the enamel tends to really decrease the Q w/r to air spaced wire. And, as you said, copper tarnishes very fast and
covers in a layer that is almost insulating, whereas silver, even tarnished, remains very conductive.
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