Green oxide on copper plated bars

[drax]

We use pre-plated silver plated copper bars, on the edges it is bare copper. This can develop a green oxide over time. Could this hurt anything, can it creep into the silver plated areas?

thanks,
Mark Faulkner

 

[kenvlach]

Yes, the green patina* is a corrosion product that could undermine the silver plating.

Possible solutions for the exposed areas: Brush plating of silver, brush plating of tin, application of plastisol (brush-on vinyl in a solvent), application of grease or wax (I prefer Alcoa’s Electrical Joint Compound (EJC) No. 2), or painting.

*the green patina is not an oxide; it consists of malachite (basic copper carbonate, CuCO₃Cu(OH)₂) and usually lesser amounts of brochantite (basic copper sulfate, CuSO₄3Cu(OH)₂) and atacamite (basic copper chloride CuCl₂3Cu(OH)₂).

The copper oxides are the red cuprite, Cu₂O, and the black tenorite, CuO.

 

[drax]

I was told this green patina was a super conductor...yea, by another engineer! I don't think so. I believe this will increase the resistance of a joint and cause heating. If I had this corrison on the edge of a bar, would it spread on other plated areas or is it local.

thanks in advance

 

[kenvlach]

Super conductor?????????? told…by another engineer??????????
Check whether he majored in humor.
Of course, you could sinter the copper compound with Y₂O₃ and BaO in the right proportions to create the ‘1-2-3’ superconductor, allowing a much smaller busbar (provided it was kept in liquid N₂).

Yes, of course it will increase the resistance.

Yes, it will undermine and lift off the silver plating. Since silver is galvanically noble to copper, the reaction may be more rapid at the interface.

Is the silver tarnished? If not, perhaps it was chromated or lacquered.