Just when you thought this thread was dead....
>From: rattmann, rattmann@cts.com
>
>>Several people wrote to me describing Noalox as a greenish substance that
>>contained no conductive component -- that it was merely a chemically
>>neutral grease. They explained that this material wasn't suitable for
>>antennas since it didn't improve the conductivity of the joint.
>
>I've used No-Al-Ox for about 25 years on various yagis here and around the
>world, with good results. It works great.
>
>The "conductive component" argument is bogus. The function of the material
>is not conductivity per se, but rather it is to enhance existing
>conductivity between the two aluminum pieces. It does this by excluding
>oxygen from the joint, preventing formation of new aluminum oxide, AFTER YOU
>"SCRATCH THROUGH" the original oxide while the pieces are coated with the
>stuff. You do that with a small stainless-steel wire brush.
Now wait one second. I'm not metallurgist, but I do know enought about
the properties of aluminum to know that using a wire brush to remove
aluminum oxide from the surface of aluminum only works in an oxygen-free
environment.
On contact with air, metallic aluminum reacts quite quickly to form
aluminum oxide. Unlike its iron counterpart, aluminum oxide clings pretty
tenaciously to the aluminum, producing a tough outer barrier about 50
molecules thick. Aluminum oxide itself isn't bad, since it serves to
protect the underlying metal, and it is about as conductive as aluminum.
On aircraft, special pieces of aluminum are often used, with one alloy
comprising the bulk of the sheet, and the surface bonded with a different
alloy which bonds well with the oxide.
I was under the impression that an anti-oxidant was designed to prevent
more corrosion from occurring in an aluminum/aluminum joint (as might
occur then other chemicals are introduced, perhaps carried with the
introduction of water or from contact with dissimilar metals), and to
permit the joint to be separated later on (unlike the boom on my A3S,
which after 4 years has become one solid unit).
Aliminum oxide is a pretty tough finish. Bonding other finishes to the
surface of the metal involves some interesting chemical processes.
Bill Coleman, AA4LR Mail: aa4lr@radio.org
Quote: "Not in a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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