I've noticed that almost all gold-plated connectors are made of brass instead of copper. Is there any problem gold-plating copper? I do have
some speaker spades that are gold plated directly on bare copper, so its doable, but I'm wondering, given that it doesn't appear to be
commonly done, if there's any catch to it that I should know about if I were to be DIY gold-plating.
Also, nowadays some connectors with a silver substrate are rhodium plated. What benefit could rhodium plating have over gold (or is it just for
looks, to preserve the silvery color), and again, is it something one can easily DIY?
Finally, does silver even need to be plated? While sterling silver tarnishes due to the copper content reacting with sulfur in pollution and sweat,
I've not seen fine silver tarnish. Doesn't the thin silver oxide surface that forms prevent further oxidation, or is the situation instead
like with iron, where rust does not provide any protection?
[Edited on 11-7-2005 by Quince]The_Davster - 10-7-2005 at 21:36
I think connectors are mad out of brass as opposed to copper because brass is stronger than copper, you do not want your stereo plugs to bend no do
you?
I have a 1 troy oz bar of 99.99% fine silver, and it most certainly tarnishes in air, although slowly. Before I dissolved my previous bar in nitric
acid it was very darkly tarnished by the Ag2S coating on the surface.Quince - 11-7-2005 at 00:00
That's weird. My XLR connectors have bare silver pins and there's no visible tarnish after some months sitting unplugged. Then again, I
haven't touched the silver with bare hands. But maybe I'll do the rhodium plating, if I can find out how, and rhodium, that is.
It says rhodium dissolves in hot sulfuric acid. Can one plate directly from this solution?
[Edited on 11-7-2005 by Quince]unionised - 11-7-2005 at 01:32
How fast Ag tarnishes depends on how much sulphur is in the air.
Rhodium, accoring to the Merck index, is not attacked by acids, not even aqua regia. You might be able to disolve it in Br2/HBrQuince - 11-7-2005 at 01:38
The question is, can I plate with such a solution. Also, XLR connectors are supposed to be self-cleaning, so I'm wondering if the plating is
hard enough to withstand the plugging-unplugging action.
[Edited on 11-7-2005 by Quince]Lambda - 11-7-2005 at 01:40
Brass is extremely easy to work with on a lathe. Take a look at the fine thread used in the valve system of a gas lighter. It is selflubricating and
gives nice spanders that easilly move away from the cutter. Brass can be poured into a mold at a lower temperature than copper, and is tougher and
harder. Zink is cheaper than pure copper, and so is brass (Cu + Zn).
Gold is soft, and rhodium hard and wear resistant and has about the same chemical resilliance. It has a bright shiny silver color.
Your XLR connectors most probably have nickel-plated brass pins. They allso use phosphor-bronz as pin material where springyness is required, like
banana-jacks.Quince - 11-7-2005 at 02:22
No, the pins are bare silver (Neutrik NC3FX, etc.). XLRs were designed to be self-cleaning, which is I guess why bare silver is OK. The gold plated
ones are actually more expensive, but it probably doesn't last well with heavy duty plugging-unplugging.
I guess bare copper is the worst small signal connector, since the copper oxides are semiconductors.
Banana jacks are pretty bad connectors, about as bad as RCA. For speakers, binding posts are much better because when they're screwed really
tight, it makes for an excellent connection, and the contact surfaces are pretty much airtight.
It's funny you say brass is cheaper than copper, because when I bought a copper sheet locally, the same size brass sheet was more expensive by
50%. Though I suppose it may have been some special alloy or something. Copper is much easier to shape by hand, but needs coating to prevent
oxidation.
[Edited on 11-7-2005 by Quince]neutrino - 11-7-2005 at 05:31
Does silver passivate? I thought it didn't because its oxide is so unstable.Quince - 11-7-2005 at 06:07
What does it mean to passivate? In what sense is it unstable (i.e. what are the decomposition products)?
[Edited on 11-7-2005 by Quince]Oxydro - 11-7-2005 at 07:14
Passivation is where a material corrodes, but the corrosion products stick to the surface and protect it. Ideal example is aluminum. It has
practically no resistance to corrosion, in fact it will react immediately with oxygen in the air, but it appears less corrosion-prone than iron,
because the aluminum oxide layer adheres so well that it prevents air from reaching the aluminum to corrode it. Iron oxides on the other hand flake
off the surface, offering no protection.
Silver oxide (Ag2O) is not unstable in that is decomposes; however it is quite reactive. It is an oxidiser; the MSDS says it is incompatible with
"most common metals, ammonia, magnesium, many organic materials"
How to gold plate copper
ProfMadScientist - 11-7-2005 at 07:27
Copper is the usual material for circuit board connectors, but it oxidizes and corrodes (which is not good for low voltage connections) (Higher
volatage AC connections are less sensitive to this).
When gold is plated directly onto copper, the copper will diffuse through the gold and the gold into the copper. For thin coatings (any practical
commercial coating), this is not good, as the copper diffusing to the surface will oxidize or corrode.
So, first, a nickel layer is electroplated onto the copper first. Nickel is much more resistant to diffusion of the gold atoms. Then a thin layer of
gold is deposited onto the nickel layer.
For high amp switches, the best quality ones, such as those used in Mercedes Benz cars, use thick silver contacts, which have a higher conductivity
than copper and last longer. Most cars use copper contacts for switches, though some are coated. This doesn't apply to electronic connectors,
just to relatively high amp switches. Gold plating is too thin to withstand erosion from electrical sparks or arcs.Quince - 11-7-2005 at 07:48
I scratched the spades. There's no nickel in between, but the gold plating is visibly thick. I don't know why they went that route.
Rhodium plating is much harder than gold. The problem is that it's damn expensive.
Any suggestions on whether the rhodium dissolved in sulfuric acid can be used to electroplate, or do I need to change it to some other compound first,
or put in some additives or whatever? Milligram quantities of rhodium are cheap on eBay as pendants and other stupid trinkets, but I'd still not
like to waste it in an experiment that will fail. And how should I pretreat the silver surface to remove any oxides and sulfides?
