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Re: All that glisters is not gold



At 14:59 2/9/99 -0800, you wrote:
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


There have been threads on newsgroups associated with significant
experience in this area. I recall in particular, that the practice of
plating microwave components with silver was not an unqualified success,
according to a source said to be associated with the US Navy. This entity
recycled oxidized components for replating, apparently.

Plated waveguides are sometimes nitrogen-filled for weather and oxidation
protection. But the biggest danger from injudicious silver plating can
arise from the jewelry grade alloy which may be applied, and which can show
greater resistivity than bright copper.

Gold is preferred for long-lasting contacts on account of its stability.
Informed usage is through a gold film, not along...

Some values for the pure materials:
Cu 1.7E-8 ohm.meters (for comparison 70:30 brass abt 8E-8)
Ag 1.6E-8 (strong alloy 5E-8)
Au 2.4E-8
Al 2.65E-8

Brian



brian whatcott <inet@intellisys.net>
Altus OK