Re: All that glitters is not gold

[Stan Dodds <dodds@RICE.EDU>]

I think you have the right idea. The bulk resistivity is, of course,
not changed by surface corrosion, but contact resistance is. Gold is
plated onto switch and connector contacts to prevent corrosion and
maintain low resistance at the contact point. The bulk material of
contacts is usually a copper alloy, chosen as a compromise between
conductivity and 'springiness'.

Silver would be a wonderful bulk conductor for wiring etc. but copper
is a lot cheaper for most applications. (I have been told that silver
was used to carry heavy currents in the calutron isotope separation
facility during WWII because copper was more useful elsewhere in the
war effort.) Even so, a thin layer of silver is sometimes plated onto
high-performance waveguide components to squeeze out a little lower
loss.

Hope this helps.

Stan


> For years I've been telling my students what someone told me when I was a
> student, that gold is the best conductor, followed by silver, then copper.
> Well, a student showed me a table of resistivities of various metals in his
> text (Serway, 4th ed., p 777) and, low and behold, the order is silver,
> copper, then gold. Could it be that this is the order in their PURE form,
> but that the resistivity changes significantly due to surface corrosion so
> that in practice gold wins? If I remember my chemistry, gold is not as
> reactive as silver or copper.
>
> P. Goodman