Solving the Mystery of PVC Wire Insulation Corrosion

[jim hardy]

Over about the last decade I have encountered with increasing frequency a black corrosion on the strands of copper wire.
When you strip the wire it'll be jet black instead of old copper brown.
It cannot be soldered.
It is a real nuisance when trying to repair something like an automobile headlamp socket or an extension cord that needs a new end.

It used to be somewhat unusual, then it seemed to be most frequent on particular colored wires, nowadays it's prevalent. Three questions:

1. Might this coating be copper sulfate ?

2. Might it be caused by sulfur bearing organotin stabilizers in the PVC insulation, as metal based ones are phased out?? (##&I@#!@&^ that 9** partiple EPA )

3. What will dissolve it and leave me with shiny copper that I can solder?
I've tried MEK, alcohol, acetone, paint stripper, salt & vinegar to no avail. Scraping gets only one face of outside strands leaving me a joint that I don't trust for high current.

This is aggravating handymen worldwide, just try a search.
Sure would appreciate some education here as well as practical advice .

This is a business opportunity - bottle a cure .
It's about the only product i'd order from those annoying TV ads.

Thanks for any help at any level .

old jim himself

 

[AlephZero]

I would guess copper(II) sulfide (not sulfate, which is blue) or copper(II) oxide.

If it is sulfide, try cleaning with ammonia solution. Otherwise, I think this is going to a tough one to remove chemically. The oxide dissolves in potassium cyanide - but anything that reacts chemically with the oxide or sulfide will probably react with metallic copper as well.

http://en.wikipedia.org/wiki/Copper_monosulfide
http://en.wikipedia.org/wiki/Copper(II)_oxide

 

[jim hardy]

I might have arrived at a partial answer by blind luck.

After more reading, the black stuff is more likely copper sulfide(? .. chemistry is not my strength. )

EDIT oops Aleph posted while I was typing THANKS !

Adding just a few crystals of copper sulfate biocide from the farm supply store to my salt&vinegar solution turned the black stuff to a copper color, albeit a dull one.
Rinsed it in baking soda then applied flux and it readily took solder .

That has rescued a hundred dollar extension cord (200 ft #12) that only needed a new receptacle end.
Total expenditure:
$0.59 for receptacle
$0.19 for outlet box
had everything else on hand.

I hope this helps somebody with a car , boat or household repair.

Industry needs to know if PVC stabilizers are corroding the wires they insulate - it could cause something that's important to fail.

old jim

 

[jim hardy]

Thank you Aleph I didn't think of ammonia and don't know why

will try that too. Makes perfect sense.

 

[alphy]

I understand your frustration with this issue and I can assure you that you are not alone in encountering this problem. The black corrosion on the copper wire is most likely caused by a reaction between the copper and the PVC insulation. PVC is known to release hydrogen chloride gas when it is heated, and this gas can react with the copper to form copper chloride, which is black in color.

To answer your first question, it is unlikely that the coating is copper sulfate. Copper sulfate is typically blue or green in color, not black. It is also not commonly used in PVC insulation.

Your second question raises a valid point. Organotin stabilizers, which are commonly used in PVC insulation, can contain sulfur and may contribute to the corrosion of copper. However, it is difficult to pinpoint the exact cause without further testing and analysis.

As for your third question, unfortunately, there is no easy solution to this problem. The black corrosion is a chemical reaction that has altered the surface of the copper wire, making it difficult to remove without damaging the wire. It is not easily dissolved by common solvents and scraping may not be effective in removing all of the corrosion.

In terms of practical advice, the best solution would be to prevent the corrosion from occurring in the first place. This can be done by using wires with a different type of insulation, such as polyethylene or cross-linked polyethylene, which do not release hydrogen chloride gas when heated.

In terms of a business opportunity, there are already products on the market that claim to remove corrosion from copper wires. However, I would caution against using these products without proper testing and understanding of their ingredients, as they may cause further damage to the wire.

I hope this helps to shed some light on the issue and provides some guidance for future repairs. I am always happy to see people taking an interest in understanding the science behind everyday problems.