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Re: [TowerTalk] Black on Cu

Subject: Re: [TowerTalk] Black on Cu
From: "Donald Chester" <>
Date: Wed, 06 Sep 2006 03:03:27 +0000
List-post: <>
The copper is already green.  The original wire was salvaged from old 
open-wire railway telegraph lines.  The sulphur from years of coal-burning 
steam locomotives gave it a good  coating of copper sulphate.  Open-wire 
telephone wires that I have seen were always (very rusty) steel.  I suspect 
the railways used copper clad steel because it would last much longer in the 
environment of coal fumes that plain or galvanised steel, and not because 
copper is a better conductor than steel.

The black stuff forms right on top of the green coating.  The green coating 
is very hard and must be scraped off with a knife or sandpaper to expose 
bare copper, but the black stuff is loose, and can be rubbed off with the 
fingers, just like soot.  And just like soot, it is very dry and has a soft 
feeling to the touch, not gritty or oily.  The green CuSO4 patina seems 
unaffected by its presence.  When the black is rubbed off,  the copper 
sulphate coating underneath appears intact.  That's why I am not sure if it 
is a simple a chemical reaction with the copper, or a living organism.

Normally, copper that is not exposed to coal fumes around here just turns 
brown, like a used penny.

The wire in question is #10 copper-clad steel.

I have used the stuff for ground radials, and it does turn green when buried 
for a long time in the local soil.  However, I have pulled up copperweld 
that has been buried for over 30 years, and very little, if any, of the 
copper jacket appeared to be eroded away.  I  occasionally check my present 
buried ground radials (#12 solid soft-drawn copper) and they, along with the 
silver-brazed connections to the ground bus, appear intact, except for mild 
surface corrosion.  With buried copper wire, the green tint doesn't appear 
until it is thoroughly dry.  When freshly pulled out of the damp soil, it is 
sort of brown.  I think a copper radial system would last for decades in 
this soil.  As I recall the last time I used a soil analysis kit, it tested 
pretty close to neutral, PH-wise.

We do have a large coal-burning electric power plant a few miles from here.

My galvanised tower has to be protected from rain runoff dripping from the 
copper wire.  Otherwise, enough copper leaches off the wire to eat away at 
the zinc coating, causing it to develop a greenish corrosion.  I made some 
rubber drainage tubing out of old automotive hose stock, and that keeps the 
runoff from the wires from dripping onto the surface of the tower structure.

Don k4kyv


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