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Old 24th Dec 2019, 11:29 pm   #1
Argus25
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Join Date: Oct 2016
Location: Maroochydore, Queensland, Australia.
Posts: 2,679
Default Copper anti-corrosion experiments

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.
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