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Re: RF conductor materials (fwd)
---------- Forwarded message ----------
Date: Thu, 30 Apr 1998 06:01:26 -0700
From: Jim Lux <jimlux-at-earthlink-dot-net>
To: Tesla List <tesla-at-pupman-dot-com>
Subject: Re: RF conductor materials (fwd)
----------
> From: Tesla List <tesla-at-pupman-dot-com>
> To: tesla-at-pupman-dot-com
> Subject: Re: RF conductor materials (fwd)
> Date: Wednesday, April 29, 1998 9:29 PM
>
>
>
> ---------- 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.
> >>>>
> Aluminum
> 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
Also, Aluminum cold flows more than copper, so that screw connection that
was tight when the house was built 10 years ago, isn't anymore. With "wire
nuts" which are spring loaded, the issue isn't quite as severe. That, and
the aforementioned higher resistance oxide spots, etc. etc.
There are a variety of proprietary preparations that can be used on
aluminum conductors to allow their use. AlNox is the one I am familiar
with. I've used it on aluminum antenna elements and the like.