Copper and steel electrolysis?

N

nakadnu

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Dec 9, 2011
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I am modding my Cold Steel true flight thrower. I am considering taking scrap copper pipe, splitting into a sheet and possibly wrapping it around the tang to form a handle. Not real sure how I will do this but I think a copper handle would look pretty cool.

My question is ; will copper and carbon steel cause electrolisys and promote corrosion? Anyone have any experience working with copper like this or any input? Thanks.
 
Copper and carbon steel will form a galvanic couple. If one the designers at work wanted to use that combination, I would tell him, "NO"
 
I don't know anything about the subject but wouldn't you need to have it in solution? Not arguing just curious. There are makers who have used copper bolsters and such.

From wiki
Galvanic corrosion is an electrochemical process in which one metal corrodes preferentially to another when both metals are in electrical contact and immersed in an electrolyte. The same galvanic reaction is exploited in primary batteries to generate a voltage.
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Galvanic corrosion is a problem when joining new copper plumbing to old steel pipes. Steel will corrode in preference to copper. But unless you are making a knife that will constantly be exposed to moisture and will not be properly oiled and cared for, it should be a non-issue. I suspect the bigger issue will be the change in the balance of the knife if you plan on throwing it...copper would make a fairly heavy handle.
 
I plan to wrap the copper sheet around the tang. This would leave a space for sweat, blood etc. That is my concern about corrosion/electrolysis. I am not using this for a throwing knife. I plan to use it as a "bushcrafter beater". I cut the hilt off, ground off the black coating and soaked it in vinegar for a gray patina. I dipped the handle in Tool dip, this is a rubber coating much like you see on pliers etc. It didn't work out as I planned. After dipping it 4 times I ended up with a coating less than 1/16 of an inch thick. Another thought is to wrap it in cord and then do the tool dip over that. I figure a $20 investment in a fairly good knife and I can do some experimental customizing.
 
A copper handle will probably not cause corrosion under any normal conditions, but will also probably not be a good Bushcraft handle.

Try wrapping the handle with paracord and then painting the cord with thin epoxy. Brush it on lightly and let it soak in. Once it stops soaking in, wipe off any excess and let it cure. Check it as it cures, and turn the knife so drips don't form. Wipe off any drips that start to form with a cloth dampened with some acetone. Once cured the handle will be water proof and super robust, as well as a good grip. You can buy the paracord from many places in all sorts of colors for very little .
 
bladsmth said:
A copper handle will probably not cause corrosion under any normal conditions, but will also probably not be a good Bushcraft handle.


I assume you mean because it would be slick and not have good traction. Otherwise can you elaborate? I prefer to do something original and unconventional yet useful. I do everything in my living room, unless the weather is cooperative and I can work in the yard and I have kids, so my options are limited.
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Copper will tarnish, and stain you hands. It will also be loose fitting as you describe it. It is slick as you pointed out, also. In the assembly you described, it will trap water and such under the handle and the steel will rust ( without any need for electrolysis).

The sealed paracord handle will be tough and waterproof. You can use many materials if you want a non-conventional look. Rattan could be used and coated the same way and make a really neat "natural" style handle. The same could be done with burlap,jute twine, cloth,etc.
 
All good points Bladsmth. I am mulling these things over in my mind when I am trying to sleep at night.
 
Gents, where I come from, it does not take a whole lot of moisture to activate a galvanic couple, especially one with as much dissimilarity as carbon steel and copper. Atmospheric moisture can be enough. Encapsulating the connection in resin would likely work. Lay down a layer of tool dip, then wrap it with cord and dip it more.
 
Solder just adds more metals to the galvanic party. Depending on the alloy, something in the solder might, or might not, corrode in preference to the steel or copper.

The problem is solved in plumbing with an "anti-galvanic coupling", basically a "plastic" non-conductive pipe fitting that goes between dis-similar metals.

You could probably solve the problem in a similar way by putting a layer of non-conductive epoxy between the steel handle and the copper, which would also solve the problem of sweat and fish guts getting under the copper. Traction could be improved by bead blasting the copper, or checkering it with a file.
 
So... what your all saying is.....

.......this isn't the best idea? :o:o

What's the prognosis?
How long does it have to live?



My question though, is: How have hundreds of centuries old Japanese swords with copper habakis survived so nicely without the effects of electrolysis.
 
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Electrolysis needs something to "complete the circuit" like slightly impure (hard, salty, or acidic) water. If you keep the knife dry and lightly oiled, (pretty standard care for a Japanese sword) it should last centuries.

Nice knife BTW
 
Would this be a worry with only copper or with other metals also? Say silver solder, and brass to steel?
 
Short answer - The real word risk is probably small on a knife that is taken care of.

Big Blues' knife will not automatically start to corrode unless it gets wet and is left to corrode. It would rust under the same conditions without the copper.

Copper and iron are galvanicly well separated. The more the separation, the worse the corrosion problem due to galvanic action. Other metal combinations are less active. The situation is also acerbated by the fact that both metals will oxidize easily all by themselves. Add low Ph water and some electrolytes, and it can get nasty.

Vaunripped asked about silver solder...and he is right to consider this where there will be continues exposure to electrolytes. The Thresher submarine disaster was possibly caused by the silver solder joints failing due to galvanic corrosion. Under the conditions a knife will be used, it is not a concern.

The physics of it is that the metals should be less than .25-.50V apart in galvanic potential. The more harsh the electrolytic conditions ( like saltwater), the closer they need to be. Nickel, copper, brass,bronze ( common knife hardware materials) all have a galvanic index (GI) about .30-.40V. Steel is about GI .89-.90V. Thus these items would corrode by galvanic action if left wet or in water. Copper, Brass, and nickel however will last almost forever when used together, which is why they work so good in sculpture and statuary.

Some of us are old enough to remember making a battery from a pennies and dimes,spaced with blotter paper , and soaked with salt water ( back when pennies were copper and dimes were silver). The potential difference is only .20V between these metals, so one penny/dime unit ( a cell) will only make a .20v current. But when we make a stack with eight of each ( a battery) then we get 1.5V ( there is some loss due to resistance).
A near perfect battery would be gold and beryllium, but zinc and carbon are far cheaper and more plentiful.
 
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On Bigblue17's knife pictured above, wouldn't a coating of epoxy between the tang and copper prevent electrolysis? The only reason I ask is that I've use 0.060" brass sheet for liners on full tangs and have thought about using 0.060" copper for liners; I just haven't gotten around to it yet.

randy
 
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