conductivity of gold

[Unregistered]

Hi all
Have been wanting to ask this question for a while as I have seen nothing about it on forums.
The conductivity of gold I have seen in many areas associated with PI detectors is as they say "low conductance". I have thought that gold was of high conductance or of good conductance up there with copper. Why do they use it in many electronic instruments if it was not for its condcutance and its inability to corrode. Or am I looking at this in the wrong context.
Maybe I am .. can someone explain this "low conductance" .
thanks
george

[Max]

Hi all
Have been wanting to ask this question for a while as I have seen nothing about it on forums.
The conductivity of gold I have seen in many areas associated with PI detectors is as they say "low conductance". I have thought that gold was of high conductance or of good conductance up there with copper. Why do they use it in many electronic instruments if it was not for its condcutance and its inability to corrode. Or am I looking at this in the wrong context.
Maybe I am .. can someone explain this "low conductance" .
thanks
george

Hi george,
take a look at:
http://www.eddy-current.com/condres.htm

there is a table with conductivity for various metals/alloys.

here is another, simpler:
metalresistivity,
nano-ohm-metersilver14.71copper15.80gold20.11aluminum25.00zinc54 .55iron87.10lead193.00mercury983.96


In PI detectors what's important is target signal decay time, and every target has it's own decay model. Composition play a major role in decay curve of a specific target, so a rough kind of discrimination is sometimes possible between e.g. iron and gold items.


For PI target gold model also take a look at this article (part 1):
http://geotech.thunting.com/pages/me...byn/corbyn.pdf

Best regards,
Max

[Unregistered]

context

Hi Mike
as i thought I am looking at in the wrong perspective.
Thinking low conductance was poor and high conductance was better.... its all on how you interperate it .
no problem
thanks
george

[bugwhiskers]

Hi George,

I too have been confused by posts referring to gold as being of low conductivity which is the opposite to resistivity....electrically. I think the people that refer to gold as being of low conductance are really referring to it's magnetic properties. Ya juz gotta love standards !

regards
bugwhiskers

[Reg]

Hi guys,

Gold is not as good of conductor as silver or copper and the charts are correct. However, gold is basically inert also, so it doesn't oxidize or corrode over time either. This is the key as to why it is used.

So, contacts or connections are generally coated with a very fine layer of gold to assure they will always make a good contact that will not be affected by moisture or other adverse condition.

Generally, this coating is very thin so the low conductance isn't a problem. Instead, it merely keeps the better conductor away from the elements and assures a good connection for years.

Hope this helps understand why gold is used to coat various electronic components.

Reg

[bugwhiskers]

Perhaps someone could tell us where in the conductance table the line separating the good conductors from the poor conductors is.


regards

bugwhiskers

[Reg]

The division between good conductors and poor conductors is probably more opinionated than one might imagine. However, typically the only truly very good conductors are silver and copper. Gold follows in line but is much higher in resistance as does aluminum, brass, etc.

If you use a TID metal detector, this becomes obvious, since the silver and copper objects will respond high on the target display meter while similar sized objects made of gold, aluminium, brass, etc will read much lower.

Now, this doesn't mean metals such as aluminum can't or shouldn't be used for carrying current or aren't decent conductors. In fact Aluminum is and has been used as have various forms of brass, etc. Generally, aluminum use is in areas of high voltage where the voltage is high and the current is much lower.

Aluminum will quickly oxidize on the surface which makes it a problem metal for current carrying applications where connections are made. This was found out back in the late 70's and 80's when some houses were wired with aluminum. Poor connections caused many fires and problems in both houses and some cars.

Getting back to the basic question and how it relates to metal detectors, once again, silver, copper and some of their alloys are considered good conductors. Gold, aluminum, brass, lead and others are generally considered low conductive metals. The difference between them will show up in phase shifts or decay dimes, depending upon the type of detector involved.

Reg