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A Question Of Conductivity


RiverRat

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I noticed early on that in discussions about the conductivity of gold, that gold is considered a low conductor.

This is confusing to me. My understanding was that gold is a high conductor, whereas only 2 other metals are higher conductors. Silver being the highest conductor, and copper being the next highest, allowed by gold. Iron is way down on the list.

Can anyone please explain this?

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Yeah, I know where your coming from here, I guess whilst gold is not as good a conductor as say copper or silver, plug a cheap USB charger cable in that does not have gold plated contacts and has been around awhile and it becomes obvious that gold is in fact with age and attack from the elements a much better surface to conduct electricity then either copper or silver, anodise Aluminium and you find the surface does not conduct electricity.  

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32 minutes ago, RiverRat said:

I noticed early on that in discussions about the conductivity of gold, that gold is considered a low conductor.

This is confusing to me. My understanding was that gold is a high conductor, whereas only 2 other metals are higher conductors. Silver being the highest conductor, and copper being the next highest, allowed by gold. Iron is way down on the list.

Can anyone please explain this?

Your understanding is correct, Gold is a very good conductor, and only copper and silver are better.

No other explanation is necessary.

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Under the term inductive conductivity in non-ferrous metals, you must first take into account that its value varies greatly depending on the size, shape .. also very strongly from the thickness of the metal! /very important/
 
The best example of round objects, for example, is the large difference in conductivity between a large silver half-dollar coin and a very small silver hammered coin ... both coins are silver, but the difference in conductivity is huge.

It is similar with objects made of gold- .. where, in addition, the purity of gold also plays a binding role ... and it is generally known that some gold alloys- .. have a significantly lower conductivity than pure gold ..

A flat or irregular shape (nugget, open circle, or defective or, for example, a crack in a coin or other object) can further reduce the conductivity of a given metal.

  Finally ...- a good test for the conductivity of metal is to compare well large, for example 1.5-2cm large / same thickness / coins ... made of different metals -Nickel, Gold, Silver, Aluminum and Bronze where you can quickly determine the relative conductivity of individual metals ..

silver coins according to conductivity ...the last rough chopped coin is made of iron alloyIMG_20210208_135916 (2).jpg

 

 

 

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It's only pure gold that's a good conductor. When it's alloyed, the conductivity drops quite significantly. Even 22 carat ( .917 fine ) has a conductivity that is one-fifth that of pure gold. And lower carat alloys often have nickel in the mix, which is particularly bad for conductivity.[ copper-nickel alloys are used to make electrical resistance wire, for heaters, kettles, electronics resistors]

Here's a table of different metals and their conductivities:
http://eddy-current.com/conductivity-of-metals-sorted-by-resistivity/

Finding good data on gold alloys is hard, no-one is usually bothered about the electrical characteristics of jewellery, unsurprisingly.

22 carat gold is very close to pure tin on this scale, about 15% IACS.

 

Over on Tom Dankowski's forum, I posted about my attempt to make 'dummy' US 0.900 fine gold coins from tin. I used a 'lead-free' electronics solder, which are usually almost pure tin. The results were pretty close, but without any real coins to compare with, my project stalled.

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9 hours ago, Norvic said:

Yeah, I know where your coming from here, I guess whilst gold is not as good a conductor as say copper or silver, plug a cheap USB charger cable in that does not have gold plated contacts and has been around awhile and it becomes obvious that gold is in fact with age and attack from the elements a much better surface to conduct electricity then either copper or silver, anodise Aluminium and you find the surface does not conduct electricity.  

Yes.  Simply put, pure gold is used to plate small, electrical current carrying contacts because it resists corrosion which can cause a huge increase in resistivity when the cross-sectional area of the conductor is small.  The problem is that pure gold is very ductile and even small amounts of other metals are commonly alloyed with it to give it strength while retaining its visual appearance such as in jewelry.  Natural gold often has natural impurities as well.  As others have mentioned, conductivity drops off rapidly when is less than 100 percent pure.

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There are (at least) two sources of confusion.  One is the fact that alloys have different electrical conductivity than their elemental components.  (Others have addressed that above.)  Often the conductivity is lower than any of the compoents.  Here's a post that shows the conductivity of binary alloys (gold-silver and gold-copper).  As you see this has been discussed before.  (Some silver and copper alloys are much better at keeping conductivity close to their pure forms.  Take USA coins with 90-95% of their main components being one of these, for example.)

The second problem is that the term 'conductivity' in metal detecting is different than as used in physics/engineering/metallurgy.  In metal deteting, the digital target ID (which is directly a function of the phase shift of the returned wave compared to the initial coil-transmitted wave) depends upon more than just the intrinsic conductivity of the metal.  Size and shape (see ElNino77's post above) plus orientation also enter into the picture.  Consider a horizontally oriented flat steel washer.  The hole (shape) causes stronger eddy currents than the lack of a hole; a bigger washer (size) will give a stronger signal than a small one.  As a result, steel washers can give high dTID's, even into the coin zone.

Bottom line is that (alloyed) gold items as found with a detector (see Steve H.'s post) typically come in around the middle or even low part of the dTID scale.  That's why gold gets the reputation among metal detectorists of being a poor conductor.

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When this topic comes up I usually toss in this test I did with the White's DFX and some gold nuggets. It shows how the size of the nugget has less effect than the purity and shape/porosity of the gold. The numbers are all over the place, but in general, the purer and more solid the gold, the higher the number.

Some Gold Nugget Target ID Numbers

In general, Alaska gold is lower purity than California and Australian gold, resulting in lower target id numbers. Note that a very large gold nugget will give similar readings as a 12 oz aluminum can!

gold-nugget-vdi-numbers-herschbach-dfx.jpg
Some old nugget target id numbers

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