Passivated copper

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Chuck Percy:
About 20 years ago I read a short (1/2 page) article in a ham magazine, possibly 73 or CQ, about passivating copper with household chemicals.  As I recall, it was neither particularly difficult nor were the chemicals particularly hazardous.  I have several projects in process where this would be advantageous, including a copper cactus-j pole.

Does anyone have any additional information or know how to do this?

For those who don't know, passivating is a process that treats the surface of a metal to prevent further oxidation.  It turns copper a dark tint.

John L Pawluk:
Did a google search and found this:

http://www.finishing.com/69/87.shtml

Hope it helps.

John

Darrin:
I wouldnt see the need to passivate copper, infact I dont think it's a true passivation. I dont think copper is one of those metals that is normally passivated in the true sense of the word like stainless steel or Aluminum. It's self passivating, in a way.

As you probably know, passivation is done by forming an oxide or nitride layer on the metal surface. That green natural patina you get with copper is an oxide layer and it's only slightly water soluble so it doesnt dissolve quickly and protects the metal underneath which is what you want. It's not a hard "passivation" layer but does the same thing.

Both patina or passivation would have similar RF effects, which I think would be real hard to notice on an amateur antenna. I think you'd be better off painting it or using aluminum if you're worried about it. But, really, I wouldnt worry about that 0.01 dB difference.

Anyway, I seem to recall you can form a fast oxide layer on copper with hot vinegar or citric acid (lemon juice).

FYI: I have some copper pipes that have been laying out in the yard for 5 years. They're black from oxide. But, if I lightly sand away the oxide, the metal underneath is still bright and solderable.

Hope that helps?

Chris J. Smith:
Instead of passivating the j-pole, I'd use a clear coat paint type of covering.  Krylon makes one which I have used on many occasions, it works well and has little or no effect on the RF characteristics of the antenna.

Steve Katz:
I'm trying to figure out why anyone would want to passivate copper, especially for an antenna.

To change the way it looks?  I'd guess that's the reason, because it certainly won't change the way it works, now or in the future.

Instead of passivation, if I want to remove the "shine" of a new copper antenna so it doesn't attract attention, I usually just spray paint them with dull camo colors.  That works, and only takes a minute.

WB2WIK/6

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