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Argus25 24th Dec 2019 11:29 pm

Copper anti-corrosion experiments
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A while ago I discovered that a thin film of WD-40 left on a bare copper plate encouraged a type of fine brown spot corrosion. The experiments further suggested that there was no chemical reactivity of the WD-40 itself to the copper, that it was probably due to a type of Hygroscopic effect. A large pool or well of WD-40, which largely excluded atmospheric water vapor prevented the problem.

The WD-40 was particularly good at preventing rust on bare steel, but a film of it did induce the spot corrosion on bare copper & brass.

The question really was, what would be the better lubricant for IC sockets in vintage computers which have a copper component and better general metal protector. Or what might suit a switch contact. There is a WD-40 specialist range anti-corrosion spray, but I have been unable to acquire any in AU.

I had been looking for alternatives, so I set up a fresh copper plate to compare 5 easy to get products:

WD-40 (Spray)
Caig Chemicals DeoxIT Gold G100L (Yellow liquid)
Selley's RP-7 Multipurpose Lubricant (Spray)
Inox mx3 (Spray)
Inox (Lanox) mx4 (Spray)

I applied these to a fresh copper plate and waited 2 weeks. Photo of plate attached.

As noted (and matching the first WD-40 experiment) fine brown corrosion spots appeared where the WD-40 was applied. The same sort of thing with the Lanox, except that the spots are less frequent and bigger in diameter. So likely again its not chemical reactivity but some sort of hygroscopic effect.

The Gold G100L had a surface tension effect where it would bead away from the metal in places and a very subtle degree of chemical reactivity with a faint blue tinge, that I had seen on a previous experiment. No brown spots though. It was intended for gold plated connections though, not bare copper.

The Selley's RP-7 left a thin film, thin enough that rainbow colors could be seen in places, no brown spots and no surface tension issues.

The Inox mx3 the same as RP7, but it left a thicker more oily film.

So it appears from these experiments that where protection & minimal lubrication is required, say IC sockets, RP-7 is the product to use and if a little more lubrication is required, say switch contacts, the Inox mx3 would be better.

I would encourage vintage electronic restorers to repeat these experiments and test other products where possible to find out if there are other good choices too. There are many oils of course, three in one & other grades, but whether these could be as good at rust and corrosion prevention compared to more complex products like RP-7 or Inox would need to be tested.

emeritus 25th Dec 2019 12:20 am

Re: Copper anti-corrosion experiments

Argus25 25th Dec 2019 1:36 am

Re: Copper anti-corrosion experiments

Originally Posted by emeritus (Post 1201944)

Vaseline (petroleum Jelly) is certainly good for water proofing, but its a little thick/gelatinous.

Also, for example, the Inox mx3 claims it contains no petrolium distillates, kerosine or petrochemical solvents, so its safe on plastics and electrical components etc.

The RP7 however leaves a very thin protective film and not obvious to see.

So I don't think vaseline is a great option for IC pins & sockets, or switches with lightweight contacts.

In repairing vintage computers with multiple IC sockets, there is often corrosion between the dissimilar metals of the IC pin and the socket claw. And sometimes the IC pins (particularly TI types) are steel and when the silver plating fails they rust. So after they are cleaned up it is a good idea to have some lubricant and corrosion inhibitor applied in a thin film. WD-40 works, but it disappears over 6 months and there is the issue with the copper. From what I have seen so far it looks like RP7 or Inox MX3 is the better choice there.

G6Tanuki 25th Dec 2019 12:44 pm

Re: Copper anti-corrosion experiments
Is the Servisol product-range available where you are?

In times-past they did a green contact-grease. It was very sticky/claggy but I used to dissolve this in white-spirit to thin it down a lot: then it was great for use on things like the microphone-connectors and PTT-switches of bodyworn walkie-talkies.

[The sulphurous environment of something like a steelworks blast-furnace or the ammonia-ridden air of a chicken-farm soon redefines your attitude to contact-corrosion]

Argus25 25th Dec 2019 3:40 pm

Re: Copper anti-corrosion experiments

Originally Posted by G6Tanuki (Post 1202000)
Is the Servisol product-range available where you are?

I may be able to get some. If anyone has some, and a perfectly clean copper plate, it would be good to wipe a film over it and wait 2 weeks and see what happens.

My original experiments with the WD-40 involved a brass sheet with two bare steel nuts screwed to it, one as a control, put outdoors in a rain protected area. I found that the rust on the steel was very well inhibited by the WD-40, but it produced spotty corrosion on the brass. Then I tried a range of metals and found copper the most sensitive to the effect and the brown spot effect is seen indoors after 10 days to 2 weeks. So far there is still no issue detected with the RP7 or Inox mx3. I'm also repeating the experiment with a much thicker coat of RP7.

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