[TowerTalk] "anodized" aluminum

[George T. Daughters]

hi dennis,

> antenna and he cautioned about doing too much scraping.  He said it would
> remove the "anodizing" from the aluminum and it would turn black.  

if it were anodized, he'd be correct.  i'm sure you'll get millions of 
replies to this, so i'll be brief.  almost all aluminum ham antennas 
i've seen are not anodized.  aluminum oxidizes in air, creating a 
layer of "alumina" which is a good insulator, and is protective of 
the aluminum from further chemical action.  it is important to remove 
this from areas where you want good electrical connection.  the 
manufacturers all provide a joint compound that helps prevent 
oxidation at the joints... like "noalox"  NO ALuminum OXide!

> I have seen aluminum elements turn dull and gray after
> time, but I figured that was just a natural chemical process related to
> weather, contamination, etc.  

yup. that's the Aluminum oxide.
 
> I have to get the silicone off in order to reassemble the antenna, and so
> far it has resisted all chemical attacks (gasoline, turpentine, etc).  That
> leaves scraping, and probably a rotary wire brush.  

yup. that's silicone for you.  also try a medium grit sandpaper.
 
> I never thought anything special was done to aluminum tubing and it was OK
> to scrape, polish etc.  Am I wrong?  (I remember a thread on polishing
> elements awhile ago, but I don't think this was addressed).

you aren't wrong!  and as i remember, the element-polishing was 
associated with april fool's tricks.

so: clean your joints. put noalox or equivalent on them when you 
reassemble.  feed it with good coax, unless you really like climbing 
and high-altitude mechanical projects.  then, go work 'em all!!

73, k6gt
 

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