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Re: RF conductor materials (fwd)



---------- Forwarded message ----------
Date: Thu, 30 Apr 1998 05:51:05 EDT
From: Hollmike <Hollmike-at-aol-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: RF conductor materials (fwd)

Terry,
     You are right about oxidation of copper, but that shouldn't become a
problem for several years.  I know that RF heating coils are best silvered for
this reason.   When I assembled by capacitor bank, I sanded the copper plates
with some fine emery cloth just before making the connections.  I then had a
problem with arcing from one plate to the other, so made a plexiglass box for
the bank and filled it with sealing wax.  This cured the arcing problem and I
guess will prevent oxidation as well.  I would guess that copper would have to
be black with oxidation before the skin depth resistance would present a
problem at TC frequencies.  It might be resistive to the 40MHz frequency that
has recently been dicussed in spark gap operation, but I haven't thought into
that much.  I have thought about silver plating my primary, but it seemed like
too much trouble.  Maybe I will reconsider that.
    Except under extreme heat, I doubt that aluminum can do what you say.  In
all the years that I have studied chemistry, I have never heard of such an
oxidation problem.  Once aluminum forms a thin (like one molecule thick) oxide
coating, it is protected from further oxidation.  It would not make a very
good spark gap, but should hold up very well as a conductor.  I guess it would
be lousy for an induction heater coil as this might cook it to the oxide, but
for TC use it should work fine for years.  As for aluminum house wiring, there
is probably some galvanic corrosion at connection points with other metals
such as brass screws, but I was told once that the problem was that the
different metals expand differently and over years this tends to loosen the
connections creating the high resistance and then causing the fire troubles.
I used to work building high voltage power lines and all the wires I ever
installed were stranded aluminum with a steel core for strength.  the
connections were all made with aluminum connectors and bolts.  If oxidation
were a problem,  power lines would have to be replaced often.  The thin oxide
coating might be troublesome at very high frequencies, but should not pose a
problem at TC frequencies.  
   Mike