Question about galvanic corrosion

Stropping Young Lad

Stropping Young Lad

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So I’m not a chemist, and I’m only an aspiring knife maker, but I have some background in mechanical design, and this question has been bugging me.

When is galvanic corrosion a problem?

I don’t ever see it happening, even on older knives with dissimilar metals touching. Ruana knives have aluminum and steel touching all over the place. Brass guards are very common. Western used steel pins in aluminum pommels like it was nothing... so is it nothing? When is it something to be concerned about?
 
If the object is in standing salt water it galvanic corrosion can for sure be a problem. With dry between the different metals it's usually not a problem.
 
Ken H> said:
If the object is in standing salt water it galvanic corrosion can for sure be a problem. With dry between the different metals it's usually not a problem.
Click to expand...

So a brass pin in an aluminum pommel is really only a problem if you take it off shore fishing?
 
Metals will interact in the presence of a "stimulant" (water, salt water, vinegar) but it's not necessarily a problem typically. When I built our teardrop trailer, I used stainless steel fasteners to attach moldings & trim to the aluminum skins & there have been no problems with this system. It's fine in the rain, in the sun & for general towing out on the roads. If it sat in water, salt water, or was in a wet coastal climate all the time it would start to work against itself, but that would take some time.

Drop a "stainless steel" blade in salt water for a week & it may begin to rust & pit. Left out in the air, no problems.
 
If you want to see some galvanic corrosion, use brass screw-cups under the screws used to fasten galvanised fittings outdoors. The screw cups provide a little reservoir that holds water long enough for the reaction to work. It takes time. Also, in the examples of aluminum against brass or steel, it would be the aluminum that would corrode, not the brass or steel.
 
As a former chemist, I will assure you that dry galvanic corrosion in knives is not an issue.
Dissimilar metals in a liquid electrolyte will react fairly fast. This is often seen in copper/brass pipes connected with iron fittings, and in submerged parts of ships.

The subject got sort of blown out of proportion years back by the electrical caution against copper and aluminum wiring and fitting compatibility. While the electrical issue is real, it is caused by the flow of electrons causing the corrosion to happen due to a resistance barrier creating heat.

Since knives are not submerged in an electrolyte, or conducting electricity, the issue is pretty close to non-existent.
 
To expand just slightly on what Stacy said ... galvanic corrosion (as he said) is caused by the flow of electrons, and that flow requires the presence of a *closed circuit* (ie a conducting loop around which electrons can flow). One metal butted up against another does not supply that loop ... so no corrosion. Immerse in water, and the water supplies the rest of the circuit, and you can have problems (condensation on pipes serves that purpose). But ... we keep our knives clean and dry, right? :)
 
As Stacy says, an electrolyte is needed for the reaction to occur due to the different redox potentials between the two metals. Under normal conditions no reaction can occur. I would not recommend the use of aluminum on steel for example in the production of diving knives, not so much for the immersion time but as for the stagnation of water that accumulates in some types of knives (through tang with screwed back). I hope my little English is understandable.
 
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