From: Ron Kean (ronkean@juno.com)
Date: Tue May 18 1999 - 12:16:15 MDT
On Tue, 18 May 1999 02:23:08 -0400 "Michael S. Lorrey" <mike@lorrey.com>
writes:
>Ron Kean wrote:
>
>
>> In the Handbook of Chemistry and Physics, silver is listed as having
>a higher electrical conductivity than gold as well as a higher
>thermal conductivity, but the differences are not large.
>
>I'm rather surprised at that, I'll have to check my electrical
>engineering texts...And I forgot the other advantage that gold has
>over silver: it doesn't corrode.
>
>Mike Lorrey
>
>
Silver has been touted as having the highest electrical and thermal
conductivity of any metal, though it is only 5.8% more electrically
conductive than copper, copper being 33.5% more electrically conductive
than gold, at room temperature, so the differences are not dramatic.
Silver, gold and a number of other metals are commonly used as electrical
contact faces, both for switch contacts and connector contacts. Gold may
be preferred where currents are low enough that the contact face does not
have to be large, or where the voltage levels are extremely low and
unlikely to be able to punch through corrosion when the contacts touch.
Mercury-wetted contacts are probably the best for carrying extremely low
level signals; they also have the property that they make and break
cleanly (no intermittency from contact bounce) due to the surface tension
of the mercury. For health reasons, mercury contacts have to be
encapsulated, which drives up cost, so they are seldom used.
Silver, when used for electrical contacts, has the fortuitous property
that silver tarnish (aka silver sulfide, aka argentite, aka Ag2S) is
sufficiently conductive (resistivity = 1.5 to 2.0 x 10E-3 ohm-m) that a
thin layer of tarnish is not a problem in most applications.
Oddly enough, the price of gold is 50 times that of silver, whereas the
stockpile quantities of the two metals are about equal, at least within a
factor of two or three.
Ron Kean
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