[TowerTalk] Iron <-> copper tinned : Redox reaction??

[K4SAV]

I'm assuming your tower is really galvanized steel and not raw iron.

I posted this message about a year ago. It seems to go against 
conventional wisdom around here, but I got no response from anyone.  
Maybe the info is correct (seems correct to me), or maybe no one wanted 
to make the effort to reply. Anyway here it is again.

The way most people do it is to put a stainless steel shim between the 
zinc tower and the copper wire and clamp it.  Polyphaser makes clamps 
that work like that.

That said, doing it this way doesn't make any sense to me. You have at 
least three goals in avoiding galvanic corrosion.
1) Maximize the contact area of the least noble metal exposed to the 
electrolyte (water),
2) Minimize the potential difference between the metals in contact, and
3) Keep the water out.
 
1) The least noble metal in this case is the zinc tower, but the contact 
area is the same for both metals because water may collect within the 
junction but the whole tower is not going to immersed in a liquid. So 
item 1 (in the case of what is in contact with the tower) is a moot point.

2) The least noble metal will corrode.  The higher the potential 
difference, the faster it will corrode. If you look at the small list 
below, you will see this is the zinc (your tower). In order to avoid 
this you should put something as closely matched to the tower as 
possible, and let whatever comes next do the corroding (you can easily 
replace that, if need be).

In the galvanic series, in flowing sea water, in order from least noble 
to more noble:
zinc is -.98 to -1.03
aluminum alloys are -.76 to -1.0
copper is -.3 to -.37
tin is -.3 to -.33 and
stainless steel varies a lot depending upon the alloy and may be -.57 to
0.0.

Looking at this table, I can't figure out why people use stainless steel 
next the their towers. I would think an aluminum alloy would be a better 
choice. After going through this exercise, I decided to use one of the 
standard AC entrance panel aluminum alloy ground lugs (Home depot, 
Lowes, or any electrical house), since my tower requires a clamp that 
can be mated to a flat surface. I think some of these may be tin plated, 
others are not.  Don't use the tin plated ones. I used an oversized 
clamp because I liked the robust clamping screw it had. I bent the end 
of my #4 ground wire into a tight J loop, which I placed under the screw 
to gain more surface contact area. When you tighten the clamping screw, 
the copper wire actually squashes into the aluminum a little.  These 
clamps work well under a tower bolt after you file off the little ridge 
on the bottom of the clamp, and you will probably have to drill the 
mounting hole larger.

I coated the aluminum alloy to copper junction with an anti-oxidant and 
sealed it against water.  I used duct seal to encapsulate the whole thing.

Jerry, K4SAV

Beat Meier wrote:

>Hello
>
>I want connect my tower parts (6m each part) with a copper wire 35mm² 
>each leg (3 legs).
>How can I do that?
>I get copper tinned stuff with bolts which can press the copper wire on 
>one end and
>at the other end I can put it to the iron tower and paint the whole stuff.
>But my question is: Does the iron react with the tinned copper?
>And more over: If I would use cadwelding which creates copper arround 
>the connections
>this really would react havely with iron ...
>
>So what does you guys do to connect "something" to iron towers?
>BTW: The iron is the same as used for rebar ...
>Would it better to use some stuff of aluminium or stainless?
>
>Other question for the chemicals: What is the clue with the chemical 
>table of the elements i.e. which metals don't react with
>others like Gold (Au), Silver(ag),  Copper (Cu)
>This are all in the same column (11) but iron is in column 8  and Tin in 
>column (14) so what chemical values are importend to see if there
>is a redox reaction?
>
>Thanks for any infos
>
>Beat
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