Re: Electrical Properties of Brass

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <teslalist-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

Soaking in boiling salt water may actually not be what you want. Pure
Aluminum oxide is a pretty good insulator and very low loss, RF wise
(otherwise you wouldn't use alumina substrates for microwave stuff). It DOES
have a very high epsilon (ca. 10, depending).

Essentially what you would be doing is chemical passivation for an
insulating film (kind of like anodizing, but that's actually a different
process).

We do a lot of iriditing of aluminum to keep the surface conductive.

The optimum way to get a lossy surface might be to have a rough surface that
you then naturally oxidize or corrode slowly, so that you have a very long
path on the surface.

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Sunday, April 20, 2003 4:31 PM
Subject: Re: Electrical Properties of Brass


 > Original poster: "Terry Fritz" <teslalist-at-qwest-dot-net>
 >
 > Hi Ken,
 >
 > At 09:50 AM 4/20/2003 -0700, you wrote:
 > >Terry, I've always wondered about this reasoning.  Since the oxide layer
 > >has high resistance, would not there be low RF current level in it?
 > >Would that current, then, not have a much-reduced effect in establishing
 > >the RF current path?  And would not the main RF current, then, seek a
 > >path somewhat below the oxide layer, thus entering the region of
 > >relatively lower resistance within the pure aluminum?
 > >
 > >Ken Herrick
 > ...
 >
 > We have RF effects forcing the current to the outside and resistive
effects
 > forcing current in....  Exactly where the current goes and what the loss
 > is, is an interesting problem I am sure ;-))  In a few days I am getting
 > some high power RF coils that are aluminum heavy plated with silver.  They
 > work well since the currents travel in the thin silver layer.  What will
be
 > fun to see is what happens if the plating gets a crack.  We "think" it
will
 > incinerate.  But have to see for sure.  Stay tuned...
 >
 > I or Gary Lau may be able to get two coils that are exactly the same
 > dimension but one is copper and the other aluminum and test the resistance
 > on a fancy HP machine.  Soaking or boiling the aluminum one in salt water
 > will certainly oxidize it well.  I'll ask the guys that know how to run
the
 > HP network analyzer beast to see if that is "easy" to do.
 >
 > Cheers,
 >
 >          Terry
 >
 >