Author Topic: Copper anodes for galvanic corrosion  (Read 1536 times)

Dontsink

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Copper anodes for galvanic corrosion
« on: February 17, 2023, 08:47:14 AM »
Will an anode  like the one in the pic (3mm copper tubing hammered into 3mm drill hole) help with galvanic corrosion between Alu and steel and carbon?.
Does the sacrificial anode have to be in contact with the nobler materials (Steel or carbon) or just nearby will work?.
I know there is a brand that is putting anodes in their foils (not sure if it was AFS).

SUS4Life

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Re: Copper anodes for galvanic corrosion
« Reply #1 on: February 17, 2023, 09:29:04 AM »
https://galvanizeit.org/corrosion/corrosion-protection/sacrificial-anodes#:~:text=Sacrificial%20anodes%20generally%20come%20in,or%20water)%20resistivity%20is%20higher.

if you look at the list of metals, copper is toward the bottom. you would want to use magnesium.  I'm just unsure how conductive carbon epoxy matrix, you might have to sand the epoxy top coat to get the magnesium in contact with the carbon fiber.

Dontsink

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Re: Copper anodes for galvanic corrosion
« Reply #2 on: February 17, 2023, 09:45:56 AM »
https://galvanizeit.org/corrosion/corrosion-protection/sacrificial-anodes#:~:text=Sacrificial%20anodes%20generally%20come%20in,or%20water)%20resistivity%20is%20higher.

if you look at the list of metals, copper is toward the bottom. you would want to use magnesium.  I'm just unsure how conductive carbon epoxy matrix, you might have to sand the epoxy top coat to get the magnesium in contact with the carbon fiber.

I think copper and bronze are the traditionally used metals for sacrificial anodes in alu cruising yachts etc...

Maybe magnesium is better but i have this copper tube and it is easy to use,just drill&hammer into place.

For the steel bolts i could use some 1 or.5mm copper plate and cut washers to fit between the bolts and alu.Copper is soft and it will squeeze to fit i think.
Just trying to delay the alu pitting in a Gong/frankenstein setup.

Dontsink

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Re: Copper anodes for galvanic corrosion
« Reply #3 on: February 17, 2023, 09:54:59 AM »
https://www.alpinefoil.com/en/search/site/?q=Anode

I remembered wrong , it is Alpine Foil that uses an anode in the mast to alu fuse connection.

PonoBill

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Re: Copper anodes for galvanic corrosion
« Reply #4 on: February 17, 2023, 12:13:39 PM »
What's the problem you're trying to solve? In our applications, stainless to aluminum corrosion happens slowly enough to be primarily a concern for galling. Which is easily and most conveniently solved with TefGel providing both some insulation and lubrication. For Carbon to Aluminum, a bit of Cathodic protection is unlikely to resolve the problem unless you surround the junction with sacrificial anodes. The current flow will be localized and weak. Again, insulation is likely to be more effective, though nothing will ensure the aluminum doesn't get damaged over time. that's why most masts have a layer or two of fiberglass over the carbon at the junction. Carbon is off the far end of the electrochemical series, which is why dry-cell batteries have carbon anodes. Here's a good source of information on the issue:

https://compositeenvisions.com/document/galvanic-corrosion-carbon-fiber-and-aluminum/

I almost melted the joint hole of an Axis mast when I repaired the mast with just bare carbon. Adding a layer of fiberglass solved the problem though I suspect there's still a bit going on. I occasionally get a sulfurous smell when I take the fuselage off the mast.
« Last Edit: February 17, 2023, 12:15:17 PM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Dontsink

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Re: Copper anodes for galvanic corrosion
« Reply #5 on: February 17, 2023, 01:49:17 PM »
It is not so slow Bill.
I have had galvanic damage on a Gong alu fuse that was packed with TefGel and dissasembled&rinsed every couple weeks.
The damage burrows really deep before it can be seen from the outside (pitting,swelling etc).
Galvanic action has been a problem for aluminum  marine applications since day one.
Anodizing and TefGel are great at slowing down the process, but if a little anode will help i am ok with trying.The whole marine industry cannot be wrong on this matter.

PonoBill

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Re: Copper anodes for galvanic corrosion
« Reply #6 on: February 17, 2023, 06:54:03 PM »
The marine industry certainly isn't wrong, but you'd have to take a close look at how it actually works. I'm unfortunately familiar with sacrificial anodes and active cathodic protection systems. But there are limits. You need a fairly hefty chunk of metal and it has to be close to the interface, it's best if it surrounds the interface. We have kind of a worst-case scenario--stainless, aluminum, and carbon fiber. The marine industry has thrown up its hands at that combo and do what it can to avoid it. If you're going to try though, then copper is probably not the best solution. You probably need either zinc or magnesium. I don't know what Alpine does to make it work, but My guess is that it wasn't simple.
« Last Edit: February 17, 2023, 06:59:57 PM by PonoBill »
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

Dontsink

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Re: Copper anodes for galvanic corrosion
« Reply #7 on: February 18, 2023, 02:05:14 AM »
Mmm, you guys are right.
Copper may be useless for protecting alu.
Magnesium and zinc would be it...alu is in fact a good anode for many metals :).
I think i will let it go, not going to buy this stuff to protect a gong fuse that is used in lake water only.

PonoBill

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Re: Copper anodes for galvanic corrosion
« Reply #8 on: February 18, 2023, 09:28:01 AM »
It's a complex subject, the deeper you go into it, the more you realize how much more there is to know. Graphite has an electrical potential in water of +200mv. Aluminum is about -1000mv. That is literally the recipe for a battery. Current is going to flow and somebody is gonna lose an electron. It's surprising that cathodic protection works at all.

The only reason I know a bit about it is that I had a sailboat that worked very hard to turn itself back into component parts and aluminum oxide. Sacrificial anodes, active cathodic protection, bonding, shocking the shit out of myself--all just slowed the progression. I finally gave up and sold it.
Foote 10'4X34", SIC 17.5 V1 hollow and an EPS one in Hood River. Foote 9'0" x 31", L41 8'8", 18' Speedboard, etc. etc.

 


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