Removing Copper oxidation

[orion.osiris]

Hi gang,

I have some thick cables that need to be properly jointed. They're good for 300 Amps so pretty thick. Trouble is they were stored in a damp environmen t and have that black coating on the copper. This is the form of Copper Oxi de IIRC which forms when there's a limited supply of oxygen to the metal, a s opposed to the green oxidisation you get on copper roofs and whatnot. So the question is, what commonly available chemical will attack the black oxi de without damaging the copper underneath it? (Need to get it off before I solder the joints, obviously.)

cheers.

[harryagain]

I have some thick cables that need to be properly jointed. They're good for

300 Amps so pretty thick. Trouble is they were stored in a damp environment and have that black coating on the copper. This is the form of Copper Oxide IIRC which forms when there's a limited supply of oxygen to the metal, as opposed to the green oxidisation you get on copper roofs and whatnot. So the question is, what commonly available chemical will attack the black oxide without damaging the copper underneath it? (Need to get it off before I solder the joints, obviously.)

cheers.

You need an acid based flux and "tin" them with a high tin solder. (EG Bakers fluid)

ISTR that hydrochloric acid was used for cleaning when oxidation was bad. (Must be neutralised afterwards) You will need a blowlamp for the tinning and ferrules for a soldered joint. (Plus taped etc for insulating

You can get jointing kits but they usually have crimped joints and you need the crimping tool (expensive)

Dependson what sort of cable it is.

[Andrew Mawson]

Citric acid would work well if you have some lemons to squeeze, alternatively 'battery acid' ie sulphuric acid at about 2N concentration will do the trick.

The day decimal coinage was introduced I was stranded in my Morris Minor, when having to start it on the crank handle it back fired and shot the handle out, with one of the lugs cutting a neat hole in the brass bottom of the radiator miles from anywhere in Monmouthshire. I happened to have a butane cylinder and torch, some plumbers solder, but not flux. I managed a very serviceable repair soldering a 1 new penny coin over the hole using acid from the battery, and having re-installed the radiator by the side of the road continued my journey with VERY dirty hands. The girl friend at the time was suitably impressed, but not enough to overcome the dirty hands :)

AWEM

[Dave Liquorice]

Stranded or solid? Is stranded how big are the strands? Can you not just give 'em a quick rub with some fine wet 'n dry?

That is copper carbonate, reaction between the copper and weak carbonic acid (CO2 disolved in rain).

[orion.osiris]

Thanks, Yes, it's the worst case scenario: thumping thick cables comprised of score s of tiny, tiny strands - for flexibility I guess. I had some Cilit Bang limescale cleaner spray hanging around and left a tuf t of the affected cable to soak in it. After about half an hour, it had got rid of the black staining, but it still didn't look quite right. On closer inspection, the copper had attained a very non-metalic lustre the colour o f salmon pink! Not quite sure what happened there. Looked promising to star t with... Never mind, I'll try some of the other suggestions here tomorrow. I wonder if vinegar would be any good.....?

[Dave Liquorice]

Salmon pink is what copper looks like after acid attack. I think you'll find that it will take solder with a decent flux. Try it...

This'll be a welding cable then, hefty but flexable. If you'd said that in the first place I wouldn't have suggested wet 'n dry.

[Chris Hogg]

Plenty of suggestions here:

[The Natural Philosopher]

any mild acid.

including flux.

but I prefer to draw the wire through fine emery paper

if its stranded use plumbers flux but wash it carefully afterwards

[The Natural Philosopher]

that is cuprous oxide I think.

[RobertL]

Surely you should not be soldering a joint that is to carry a large current. Don't such joints have to be crimped?

Robert

[orion.osiris]

for 300 Amps so pretty thick. ....(Need to get it off before I solder the joints, obviously.)

nt. Don't such joints have to be crimped?

Depends how hot it's going to get, I would imagine. If the cable is specifi ed for the current it's going to carry, it should *never* get hot enough to de-solder. However, I do take the point someone else made about such joint s becoming prone to fracture over time...

[Tim Watts]

On Friday 09 August 2013 09:37 RobertL wrote in uk.d-i-y:

? Mains cables in the road used to be soldered - 1-2 sq inch conductors.

[Jim K]

otherwise known as copper oxide?

Jim K

[Tim+]

Yeah but, they're not really designed to be very flexible or likely to be flexed much once in situ.

Tim

[Dave Plowman (News)]

The way round that is to support the cable some way from the joint. Although crimping is the best way - but with the correct crimping tool, not pliers. And those can be expensive.

[Chris Hogg]

There are two oxides of copper: cuprous oxide aka cuprite, Cu2O, red, and cupric oxide, CuO, black. Cupric oxide, heated to above about

1025C in air, loses oxygen and converts to cuprous oxide. Cuprous oxide melts at 1235C.

[orion.osiris]

What's the green s**te you find on old copper pipes and copper flashing on roofs, then?

[Steve Firth]

IIRC mostly it is hydrated copper carbonate. Rainwater absorbs CO2 from the air and is mildly acidic (carbonic acid). It reacts with copper to form verdigris which is mostly copper carbonate.

We don't get it at all in Italy, copper turns brown not green.

[Chris Hogg]

+1

Pure copper carbonate, CuCO3, doesn't exist as such in the pure state, but the green stuff is basic copper carbonate, CuCO3.Cu(OH)2, malachite. There is also a bright blue form, 2CuCO3.Cu(OH)2, azurite. Both occur in copper ores, and malachite can occur in sufficiently large pieces for it to be made into jewellery or larger decorative items. Look on e-bay for malachite to see some examples.

[Tim Watts]

On Friday 09 August 2013 11:35 Tim+ wrote in uk.d-i-y:

Yes I agree. But the point I was contering was that "large current cables should not be soldered" which is in itself not fundamentally true.

I'd solder the cables in question and provide support for 3+ inches either side of the joint - possibly by potting inside a bit of tube or application of several layers of adhesive heastrink. Depends how much flexing is expected.