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.