Gold, Silver, Copper, Aluminum -- which is the better electrical conductor?

A. Yes you are correct.

Good luck!

A. Also better than gold is copper. Metals are nature's better conductors. Of course modern physics has invented (or should I say discovered?) superconductors. Zero resistance and they're not even metals.

A. You have to look at two different things, Justin: the resistance of the solid material that is the conductor, and the resistance of the joint (or connection / contact surface / interface, or whatever you want to call it) that the current also has to pass through. Silver has higher conductivity (lower resistance) than gold. But it tarnishes, which means a high resistance oxide/sulfide forms on its surface. Silver is fine for many things, but where a very low voltage and low current is involved (for example, in small electronic signals, such as computers and cell phones) the tarnish can interfere with the signal at the joint, and gold must be used instead.

A. Silver is the best conductor, but usually not used due to expense. It would not surprise me to see it used in integrated circuits someday, however, like copper is now (and aluminum is/was). The difference isn't a lot, but 5% is 5%.
Tarnish could be a problem for high frequencies where skin effect becomes critical.

As for superconductors, most of the commonly used ones are in fact metals. A common one is an alloy of niobium and tin. The metallic ones are used for two reasons. First, wires can be easily made and coils easily wound. This on its face wouldn't be a deal breaker. You can easily imagine depositing films of superconducting material on drum,etching it,adding a insulating layer and repeating,thus creating a large number of windings.

The real problem is that the high temperature superconductors lose that property in high magnetic fields, which happens when you use them with high currents. The low temperature superconductors do this too, but at much higher currents so they are more useful. (Super conductors are mostly used for very high power magnets).

Tarnish on silver could become critical for applications where skin effect was important (high frequencies). In fact, in high powered RF amplifiers coils are often made from copper tubing and gold plated. Although gold is not as conductive as copper, it is resistant to corrosion. If the layer is thin compared to the thickness of the layer the current flows in, most of the current will flow in the copper anyway.

If skin effect was the only issue with silver, then we could find ways to deal with that. The easiest way to deal with it would be to deposit a thin layer of a inert material (alumina?) on the surface to prevent corrosion. If it was thin and robust enough,it could prevent corrosion while still transferring enough heat and not increase the size of the wire. The final answer comes down to cost. A silver wire would cost over 100 times a copper wire. While it might be useful in a semiconductor chip, where the actual cost of the silver would be very small compared to the cost of the chip, in a speaker cable it would be prohibitive (in a satellite, spacecraft, or weapon system, it might be ok, if the benefits justified it.)

A. Hi, Gary. If aluminum's resistivity is higher, then by definition it's conductivity is lower; so aluminum is NOT a "better conductor" than gold.

However, whereas "better conductor" means higher conductivity, " 'better' conductor" might be interpreted differently :-)

Aluminum is probably a "better" conductor than gold if by "better" we mean "per unit of weight", or "per dollar spent", or things like that :-)

Regards,

A. Don't know if what I do is legitimate methodology, but when I am building Antennas, particularly high frequency stuff, I make the elements, waveguide, feedhorns, etc., out of copper, then electroplate them with silver, and then a thin layer of gold on top to prevent the tarnishing of the silver. I don't have the time or equipment to do precise measurement to see exactly what effect this has on the overall efficiency. I just figured that structurally the copper is good and easy to work with and cheap compared to the silver or gold. I figured that the silver plating would provide excellent characteristics considering the skin effect of UHF. Then to get away from the tarnish issue decreasing the conductivity of the silver, I plate a very thin layer of gold on top of the silver. I may be wrong but I felt that this should give one pretty close to the cost of the copper, with the conductive characteristics of silver and the non tarnishing characteristics of the gold. Maybe someone can tell me if the gold plate on top of the silver eliminates the conductivity of the silver? If so then the silver plate is a waste and one would be better off just plating a thin layer of gold on the copper. From what I can see it seems to work quite well, but then I reckon the gold would.

A. I want to share my experiences.

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This site is primarily about metal finishing rather than aviation, but yes, please do share your experiences.

A. Silver is a purer metal than gold, it is a better conductor than gold but honestly I think it has a lot to do with time (money in the long run) and because society (humans) have invested so much into gold throughout the generations that you will never get the truth regarding which is better because we will never be told the truth and the fact that we have relied on gold as a currency (gold is just a better decoration than silver, it always has been, read the bible even God likes toys of gold). I think we have just stockpiled so much over the generations that we have to do something with it, just think about it: the ancient Egyptians stashed it because it was pretty and their pharoh liked it (it looked better on his slave girl than silver), but look at gold's weight, its high temperature to melt down is higher than other metals, it doesn't mix well with other metals nor chemicals, and to actually make gold a better decoration is to mix it with copper). The whole debate is currency and that is it.

And also take this simple little statement from a sales perspective: wants have always paid better than needs.

Hi Gabriel. We don't censor anyone's opinion ... we welcome it. Thank you for expressing yours! But I don't agree with it at all :-)

Regards,

A. Hi Sagar. Silver is definitely the best conductor. If you had a wire of a given length and diameter made of silver and a wire made of gold with the same dimensions, you would find that the resistance of the silver wire is less.

But if you now painted the ends of the silver wire, such that you had a resistive layer of paint interfering with the ability to get electricity through the paint layer and into & out of the actual silver, you would report that there is a problem using painted silver wire for certain applications.

When silver is exposed to the atmosphere, the topmost layer reacts with the air to build a tarnish layer of silver oxide or silver sulfide which is not conductive. This tarnish acts like the paint -- it makes it difficult to get electricity into and out of the actual silver. It's not terribly important for high voltages and high currents which can just power their way through the tarnish, but for electronic circuits of very low voltage and very low current like in cell phones, the silver tarnish can be an effective insulator.

Regards,

A. Hi Vishant. I don't have the electrical engineering background in alternator design to answer your question. But I doubt that an alloy of copper and gold will be a very good conductor. My limited understanding is that copper and other metals must be of very high purity for good conductivity. I can't quickly locate a chart with the electrical conductivity of karat golds, but I do see at
http://eddy-current.com/conductivity-of-metals-sorted-by-resistivity/
that the conductivity of several copper alloys is the range of about 4% to 15% of pure copper.

Regards,

A. Hi Dave. Although you consider cable that is four years old to be relatively new, most people and most manufacturers wouldn't. You could try sending photos to the manufacturer and see if they will do anything out of good will, but I don't think they will.

It is very hard to say what is causing the corrosion. There was a Chinese wall board scandal a few years ago where the plaster was so full of sulfides that it caused all the nearby copper pipe and wiring to turn green and black. Moisture wicking up from the uninsulated ends can cause the same thing. A very cold air conditioning duct nearby could cause some condensation on the cable ends and be drawn up under the insulation by capillary action. Unless the corrosion is in the middle of the wire in a spot which simply can't be reached by environmental factors it would very difficult to assert that it was a manufacturing defect.

Surface tarnish probably doesn't radically affect the current carrying capacity of the wire, and it's usefulness for driving large speakers; but it depends how bad because if it's serious corrosion to where a lot of the copper is gone, then a lot of the current carrying capacity is gone too.

Regards,

A. Hi T. Pure copper may be your best bet because it is far cheaper and far more available that silver or gold, whereas silver is only about 5% more conductive than copper, and gold is less conductive than copper. You could google "relative conductivity chart". Pure copper wire is available from every hardware store.

Generally, alloys are not good conductors compared to purer metals -- probably related to the way free electrons can easily "bounce" from one copper atom to the next, but the path is not as smooth and easy if an atom of a different metal is encountered.

But, to avoid demerits, be very careful about using phrases like "would work better" unless you can enunciate rather precisely exactly what that phrase means to you.

Regards,

A. Hi Kiran. Who said you couldn't?

But alloys generally conduct electricity more poorly than pure metals. And what specific alloy of copper and gold are you thinking of which displays high ductility? And what exactly do you mean by "cable wire" -- because gold would be impossibly expensive for the cable wires I picture.

Abstract questions bring with them a dozen "ifs, ands & buts" that require a book to answer -- the relatively short length of forum responses mean that only very specific questions can be answered. Please get back to us with the full details of your situation, then we can probably help. Thanks!

Regards,

A. No.

Regards,

A. Good day Norah.

Try this simple experiment.
Shave off half the entire length of wood on a lead pencil, exposing the lead core.
Get a battery, does not matter what size, try 2 D cells.
Attach with copper wire one pole of the battery to the extreme right end of the lead core.
Attach with copper wire AND a flashlight bulb to the other pole of the battery to the extreme left side of the lead core and note the brightness of the bulb.
Move the copper wire with the bulb towards the right side ( towards the other pole) of the lead core.
What do you see?
Try this also with a length of copper pipe.
Hope this sheds some "LIGHT" on your question!

Regards,

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June 2016

Hi Eric. Excellent idea for a science project, which I hope Noah or someone will undertake. But a "lead pencil" is graphite rather than lead.

Regards,

Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

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June 30, 2016

A. What Ted said. I'll add this: most pencil "lead" is admixed with clay. It might not conduct electricity at all.

Even pure graphite is a poor conductor relative to metals. By 2 orders of magnitude, if memory serves.

Dave Wichern
Consultant - The Bronx, New York

A. Hi Muhil. Graphene is a special form of carbon which is a better conductor than silver. But, as we speak, it's still more of a laboratory curiosity than a practical material to make wire and bus bars from. Other forms of carbon, like graphite and diamond offer much lower to much much lower conductivity than silver. So silver would be the "best conductor".

Still, due to high cost, silver may not be a practical material for many applications either. Copper is much cheaper than silver and offers about 95% of the conductivity of silver, so it's the most common material to make wire and bus bars from.

Electrical resistivity and conductivity

Please see Wikipedia for an explanation of conductivity and a chart of the conductivity of some common materials..

Regards,

A. Although it might be a cool idea, Ganendra, because the wire wouldn't corrode if the protective coatings leaked, I seriously doubt that it is actually done. Can you quote an authoritative source that claims it is?

Regards,

A. Hi Provakar. Gold is more corrosion resistant than copper or silver, and it does not tarnish, which keeps the contact resistance low. So gold is widely used for low voltage, low current contacts -- but I certainly don't know enough about EEGs to suggest that gold is actually appropriate. I think this is a question for doctors or other specialists who do such procedures. Good luck.

Regards,

A. Hi Vipin. That question has been answered repeatedly on this page. If you don't understand the answer, that's not a problem; we can certainly try to explain it differently! But this page attracts everyone from small children in their first couple of years of school to post-doctural researchers -- so we can't understand your situation when you don't explain it but simply repeat an abstract question which has been asked & answered repeatedly already. Thanks!

Regards,

A. Few seem to have much interest in reading how to fish these days :-(

What voltage and current and frequency is carried by these contacts, Naresh? It's completely possible that neither copper nor silver is appropriate for your contacts. Neither is much good in low voltage low current electronic applications. You'll rarely go wrong with hard gold plating though. Good luck!

Regards,

Q. Hello Sir,

the plating is required in contact and also in PCB. Contacts are moveable objects and PCB is Fixed one. I need to reduce oxidation and abrasion when contact touches the fixed object. Voltage for this circuit is 5 Volt and current varies from 200 mA to 2 Amp. Now contact material is copper. I need to change material because contact wear after some time, and oxidation layer generated between contact and fixed object and contact seems to be open circuit while contact is closed.

A. Hi Naresh. There are whole shelves of books on this subject, and semester courses ... and I am not an electrical engineer. But I do see that the charging contacts on battery operated devices like cordless home phones are invariably nickel plated or electroless nickel plated -- and that sounds like the voltage/current range that you are in. Because it's a high wear application, I suspect that electroless nickel will be ideal.

Regards,

Hi Yuvaraj. That sounds like an interesting question if I understand it. You want to measure the resistance of gold while it is under strong tension or compression load, and see if those forces affect the electrical conductivity? I don't know whether it will have any effect, although my guess is it will be small so you will need accurate measurements to know ... it will be interesting to find out :-)

Regards,

A. Hi Omkar. Unplated aluminum cannot be used as a contact material because the naturally occurring aluminum oxide on its surface offers too much resistance. It is unsuitable even for house current, let alone low power digital contacts.

Regards,

A. Hi Hector. Gold is widely used for very low current digital signals because precious metals don't tarnish, and tarnish in non-conductive. Silver is very widely used for all sorts of less critical applications, and is much cheaper.

If you can tell us the actual parameters you are designing for, it's possible that our readers can offer specific advice. If you are looking for more general info, if you Google "electrical contact design course" you will see that there are any number of seminars and courses you can attend on contact design. Good luck.

Regards,