Re: RF conductor materials (fwd)

---------- Forwarded message ----------
Date: Wed, 29 Apr 1998 22:27:17 -0600 (MDT)
From: Chip Atkinson <chip-at-pupman-dot-com>
To: tesla-at-pupman-dot-com
Subject: Re: RF conductor materials

oxidize in air.  Over time this layer can become very thick. 
Aluminum oxide is an excellent insulator and is used as such in the common
form of alumina.  Copper oxide easily forms with similar results.  Since
RF currents travel on the outside surface of conductors, this can have a
very significant effect over time as the oxide layer builds up.

I have a couple questions about the above statements.  First, please
explain the difference between an enamel insulating cover and an Al2O3
insulating cover.  How can it make any difference what type of insulation
that is on a wire as far as its current carrying capabilities go?  (short
of the temperature at which the insulation burns or melts).

If the concern is reduced diameter of the conductor due
to the conversion of Al to Al2O3 then is it really such a big deal?  Even
well weathered (in the dry climate of Colorado anyway) Al has at the very
most 1/64" oxide.  
house wiring used years ago keeps fire departments busy today :-((
I believe that the reasons that Al wire is so bad are as follow:
Al-Cu connections corrode leaving small contact areas which can heat up.
Not necessarily as an effect of the previous sentence, an Al wire melts at
a significantly lower temp. than Cu.  Also, Al burns quite readily once it
gets started.  As any pyro knows, Al powder can be quite flammable.


 Chip Atkinson 
 --- If I can't fix it, I can fix it so it can't be fixed --