Protecting copper/brass from oxidising

[GMB]

I am interested to hear suggestions for protecting copper and brass items to keep them in good conductive order.

Having failed to find any probe kits for my HP 8405A I have resorted to making some with the connector made from scraps of copper and brass, and of course it is all nicely polished and shiny - but it won't stay like that for long especially when I consider the state of the metal before I started.

So what to use on it so it doesn't oxidise and then make poor contact?

[AVO_VCM163]

Probably the only satisfactory long-term solution is to plate it overall. This can be done relatively cheaply at commercial companies.
A varnish over the non-contacting parts leaving the tips bare will also provide a reasonable solution if the probes are used regularly - this abrades them and stops too much oxide forming!
I have used both methods in the past.
R

[Nickthedentist]

I don't think there's any easy answer here, other than a bit of regular maintenance.

A light smear of oil/grease/WD40 will, of course, help matters. Although they're insulators per se, they will prevent oxidation and thus help with achieving a good contact.

Nick.

[Radio_Dave]

What about tinning them with solder

David

[GMB]

I had thought about ordinary oil/grease but was worried about conductivity and damaging nearby plastic. Vaseline is suggested for car battery terminals but I don't know why specifically.

Tinning with solder was not something that sprang to mind because many years ago I tried this on board edge connectors in a TV that was having contact troubles - and it didn't work very well, in fact it made things worse.
But some lead-free solders might be worth a go. I have one that is almost pure tin. (I might try that on the next one - it's too late for heat on what I just built.)

If you Google "conductive grease" you will see silver-grease sold for improving switch contacts and the like. Anyone tried it? Everyone seems to be out of stock so not easy to try - and my concern is with the formulation as it uses a silicone grease as its base - something that is usually deadly to contacts.

[Nickthedentist]

Originally Posted by GMB

I had thought about ordinary oil/grease but was worried about conductivity and damaging nearby plastic. Vaseline is suggested for car battery terminals but I don't know why specifically.

I think a light smear of any grease would be fine. The grease will be displaced from the small area that actually makes contact. And it's reversible; you can get rid of it completely in seconds with some meths or whatever.

AFAIK, the only reason Vaseline is recommended for car battery terminals is that it's something that even non-technical people are likely to have lying around at home. If you recommend something obscure, expensive or only sold in vast quantities, most people won't bother.

Nick.

[Leon Crampin]

The reason why petroleum jelly (trade name "Vaseline") is recommended for lead-acid battery terminals is that it is acid proof. Ordinary grease of any kind will decompose in the presence of any acid or acid fumes.

Leon.

[Nickthedentist]

That's fascinating, Leon, I never knew that.

And to think I thought I was being "clever" by using silicone grease on my car battery terminals

Nick.

[Leon Crampin]

Silicone grease is also acid proof, so it will be fine - but it costs more. A further advantage of petroleum jelly is that near an engine, it runs slightly and covers the terminal post and connector with a uniform layer. Silicone grease won't melt at underbonnet temperatures.

Leon.

[GMB]

Silicone grease is also acid proof, so it will be fine

...apart from being a good insulator. I think you should normally keep silicones well away from contacts of any kind.

The worst offenders were the silicone furniture sprays which could get everywhere especially as silicones also have the properly of creeping along surfaces. This is why I am worried that a conductive grease should be silicone based - or perhaps it's a feature to stop the conductive particles getting everywhere and shorting everything out.

[Sean Williams]

Get them silver plated - I do this with RF amplifier parts at a local platers - they are suprisingly cheap in small batches - the last parts I had done consisted of a 3" diameter cavity about 10" long, and some other small parts - a good thick coat of well polished silver cost me £20!

[GMB]

I can see why that might be good for RF objects - but not sure about corrosion resistance.

I can tell all the silver plated connectors I have by the fact that they are black.

[Sean Williams]

Yes, and silver oxide conducts electricity much more than plain silver......

[Mike Phelan]

Silver develops a black coating of silver sulphide from the sulphur in the atmosphere; the way to clean it that jewellers use is electrolytically.

This is done by using a weak solution of warm sodium carbonate (washing soda) and placing the item to be cleaned and a piece of aluminium or aluminium foil in it.
There are companies that market these bits of ally made into strange and wonderful designs at a price ....
Silver will tarnish rapidly if you get rubber (gloves) or egg yolk near it.

[Mike-repairman]

Surely you could silver plate it by electrolysis yourself and then get it gold plated on top.
That would last for ages.
Not sure if you can gold plate yourself, think it involves rather nasty chemicals.
Mike.

[John M0GLN]

Originally Posted by Mike-repairman

Surely you could silver plate it by electrolysis yourself and then get it gold plated on top.
That would last for ages.
Not sure if you can gold plate yourself, think it involves rather nasty chemicals.
Mike.

Silver is usually plated in a cyanide solution as well as gold, something to be avoided, if you can get it in the sizes you need Nickel Silver is the material to use, used as electrical contacts for many years due to its resistance to corrosion and its oxide, if it does oxidise is conductive.

John

[Mike-repairman]

Hmmm, I'm sure as a lad I used to do silver plating with a solution of Silver Nitrate an electrode and a small battery?

Found this link...
http://www.practicalphysics.org/go/Experiment_284.html
Describes copper plating but Silver plating is mentioned in the Technical Notes on the page.

Sure that's how I used to do it.

Mike.

[John M0GLN]

Originally Posted by Mike-repairman

Hmmm, I'm sure as a lad I used to do silver plating with a solution of Silver Nitrate an electrode and a small battery?

Found this link...
http://www.practicalphysics.org/go/Experiment_284.html
Describes copper plating but Silver plating is mentioned in the Technical Notes on the page.

Sure that's how I used to do it.

Mike.

Hopefully not taking this OT, yes, you probably did use the method you described, its one way to get around not having silver anodes, but generally most books seem to specify a cyanide solution.

Going back back to Nickel Silver, its used a lot in the spring contacts for relays and even model electric train set rails, and is quite easily obtainable in certain sizes.

John.

[Adrenaline]

Originally Posted by Sean Williams

Yes, and silver oxide conducts electricity much more than plain silver......

Solid silver oxide is an insulator.

Try getting it into solution, and it will conduct.... good luck ;-)

[HG MICKE]

You could try using Tin Plating Crystals,These are used in solution with water at room temperature to plate copper PCB's. You just immerse the item in the solution and leave it for a couple of hours.
Crystals are avaliable from Rapid.

Colin