Hi Barry,
> So, there must be more to galvanic corrosion than just where various
> elements sit on the potential chart.
Sure is. Some materials self-contaminate with an oxide that insulates the
connection, like aluminum.
Other materials are so hard they don't conform well to the surface they are
clamping to, and that let's moisture and contaminants in that form salts
that insulate the connection.
Other materials have a wide smooth surface that distributes the clamping
force over a wide area, so pressure between the surfaces is not high enough
to force a good electrical connection.
Any material needs some type of compound to keep moisture out of the actual
contact area, like the stuff used in electrical boxes to prevent contact
corrosion. Even regular grease works, although compounds designed for this
purpose are better.
While potential difference is important, there's a lot more to this than
just using one material over another. The shape, hardness, and distribution
of pressure at the connection point is just as important as the materials
used.
Nature tries to make any rigid interface contact at only three points
against another rigid surface. I like teeth on the clamps I use, with
enough clamping force to bend or distort the two surfaces into connections
at more than three point, with lots of pressure at those points. UL is not
so caviler as to not understand all this.
73 Tom
For example, I recently purchased
> an electrical junction box to mount on the tower with some relays in
> it. In the box was a ground lug, made of some shiny metal, and it was
> labelled for use with copper or aluminum wire. Don't know what this
> ground lug was composed of.
> Any metallurgists, chemists or others with the facts that can educate
> us on the use of dissimilar metals?
> 73 Barry
> --
> Barry Kutner, W2UP Internet:
w2up@mindspring.com
> Newtown, PA Frankford Radio Club
>
>
>
>
> --
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