A Metallurgy Question - Or Not! ?

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day67

Super Member
I've always wondered why I don't see more various audio connectors/hardware made of copper with gold plate to resist oxidation?

A recent example is Cardas cartridge clips. Rhodium plated, or gold plated brass. Same with a lot of RCA parts. Rhodium, a great stable non oxidizing metal I hear, but not a great conductor. Niether is brass but they gold plate brass all the time but not copper. What gives?

With cart clips brass is probably the worst base metal as it is brittle and will just crack if the crimping pliers aren't used with care. Same with the RCA connectors. Brass is often used for the body (also not a great conductor) where the conductors are soldered, plated with gold maybe, weigh a ton, and 5X the thickness needed to deliver the signal. I know there are pure copper RCA's but the cost is prohibited for most of us.

So, is copper just not platable? I know they use copper and nickel in the chrome plating process before the chrome is applied so I always figured copper could be plated with 'bout anything.

Any thoughts on this? Inquiring minds want to know!:thumbsdn::banana:
 
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I think you may have answered your question.

"I know there are pure copper RCA's but the cost is prohibited for most of us."

Yes, I think it's mostly cost related. For instance, WBT makes Gold plated copper RCA jacks and plugs.
 
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Copper is expensive by itself, and too malleable for connectors.

Bronze (especially phosphor bronze) is much better. Bronze is copper and tin, mostly, which lowers the material cost.

Nickel and rhodium are preferred for plating connectors, as they're excellent conductors.

I was once told by an Audioquest factory guy that even a tarnished silver connector is a better conductor than gold - but people don't like the look of tarnish, so...:scratch2:
 
There are probably hundreds of brass and bronze alloys, so it's hard to say anything general. Pure copper is just too soft to make a good connector as it doesn't provide reliable spring force. It's also a PITA to machine. Machinists mostly hate the stuff, so manufacturing costs will be higher even if the copper didn't cost more, which it does. The conductivity of a bulk metal piece like a connector doesn't matter much.

Gold plating is most useful if you're mating with another gold plated connector. If not, it doesn't buy you much. Many cheaper audio connectors are just flashed with gold, to the point of being cosmetic rather than of any value after several insertions.

edit- 1tumbleweed beat me!
 
Aluminum is a better conductor... and that's why the wiring to your 220 V appliances (in the US, and if you have them) is aluminum and not copper.
 
Copper oxidizes pretty easily, so anything that involves leaving it open to atmosphere isn't a good idea. Also, like others have said, it's soft.

Copper is a better conductor than aluminum. It's a better conductor than all metals except silver. Aluminum is used sometimes because it's cheaper.

Buildings in some poor countries are wired with aluminum rather than copper for cost savings. I learned this in a materials class I took in Budapest while studying abroad. A lot of Soviet built buildings have aluminum.
 
RevMen said:
Buildings in some poor countries are wired with aluminum rather than copper for cost savings. I learned this in a materials class I took in Budapest while studying abroad. A lot of Soviet built buildings have aluminum.
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When I lived in Baltimore, my house - built in 1967 - was aluminum wired. I found this out one day when a bedroom outlet caught fire all by itself.:yikes:

Evidently it was fairly common in that time period, because copper was very expensive. I believe it's since been prohibited for new construction. I hope, anyway.
 
yeah it is weight vs. volume - my point was that folks think of aluminum as bad due to the early 1970s aluminum wiring debacle in the US (when copper was very expensive - some things never change). The aluminum per se isn't the problem; it's the connections. I presume that it's the conductivity per unit mass that makes it the wire of choice for high current applications (ovens, dryers) in US domestic service.

On the thread's topic, though - aluminum ain't great from the oxidation perspective; probably no better than copper. Gold's got 'em (all) beat in that regard (although silver "tarnish" is mostly sulfur not oxygen, as I understand it).

What I probably should've said is "phosphor-bronze is time tested and pretty darned good" and left it at that ;-)
 
mhardy6647 said:
yeah it is weight vs. volume - my point was that folks think of aluminum as bad due to the early 1970s aluminum wiring debacle in the US (when copper was very expensive - some things never change). The aluminum per se isn't the problem; it's the connections. I presume that it's the conductivity per unit mass that makes it the wire of choice for high current applications (ovens, dryers) in US domestic service.

On the thread's topic, though - aluminum ain't great from the oxidation perspective; probably no better than copper. Gold's got 'em (all) beat in that regard (although silver "tarnish" is mostly sulfur not oxygen, as I understand it).

What I probably should've said is "phosphor-bronze is time tested and pretty darned good" and left it at that ;-)
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Yes, yes, and yes. We are in complete agreement. I can't count the number of friends that have asked if the should rewire their whole house because they found aluminum wire in an outlet box.

I did learn on my current house that the jacket of an MX cable is an excellent conductor when someone uses the jacket as a return line of a three way switch.
 
1tumbleweed said:
I was once told by an Audioquest factory guy that even a tarnished silver connector is a better conductor than gold - but people don't like the look of tarnish, so...:scratch2:
Click to expand...

This is most likely because tarnish (Silver Oxide) is conductive. Oxides of Copper are not conductive. Gold doesn't oxidize. That's one of it's main advantages.
 
Let me take a stab at this.....

The problem with copper connectors is work-hardening. Bend or stress copper and it becomes hard and brittle. Brass is much more malleable and doesn't work harden.

The increased electrical resistance between brass and copper is trivial as it is basically proportional to length, (given adequate cross-section.)

Even a thin gold coating prevents both oxidation and dissimilar metal corrosions. As 1tumbeweed noted, gold and rhodium, another noble metal don't enter into electron exchanges easily - unlike sacrificial zinc cathodes on metal structures in salt water like in ships. That's why you don't hear of gold batteries.
 
From what I remember from my metallurgy class, I'm pretty sure that it is because of galvanic corrosion.
 
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