Aluminium oxide

[skenn_ie]

Hi all. Has anyone come across a solvent for aluminium oxide for use where a good electrical connection is required. The starter on an engine that I am working on has aluminium end plates, then an aluminium casting around the Bendix. I am getting a very intermittent connection between the casting and the end plate, and again between the plate and the steel motor housing. Some years ago, I came across a similar situation on a heavy duty rectifier, where the whole unit was replaced because of a high resistance between the copper of the diodes and the aluminium heatsink.

Thanks in advance.

[a64pilot]

There is a paste available at electrical supply houses that you must use for using aluminum high voltage wiring, it is there I believe to prevent oxidation of the wire, not too many years ago houses were burning down that had aluminum wiring, the wire would oxidize, heat up and the heat expansion and contraction would loosen the connection which of course caused fires.
I'd clean up the faying surfaces and use this paste, it's cheap, and or maybe install a case ground on the starter itself

I think the only thing that will remove aluminum oxide is physical force, scraping or maybe sanding

[Alan Mighty]

Loctite has a product, aluminum jelly, for removing aluminium oxide.

Perusing the Technical Data Sheet and Material Safety Data Sheet of Loctite's aluminum jelly should reveal the active agent. I would guess that it is either phosphoric acid or sodium hydroxide. Have a look at: Aluminum Jelly, Aluminum Polish, Aluminum Brightener, Aluminum Cleaner Technical Data from Loctite Adhesives

Sodium hydroxide, easily available in some inexpensive drain cleaners, might work. You need to be careful, because NaOH on Al will liberate some Hydrogen gas as the NaOH chews into the Al. Bubbles of NaOH in your eye are likely no fun at all.

Of course, once cleaned to Al, an atmosphere containing Oxygen will lead to a new film of Aluminium oxide to form fairly quickly.

[jamhass]

Most "metal-prep" compounds (used to prep metal for painting) such as Ospho, MetalEtch, etc, will work fine. They are mostly phosphoric acid, often with some inhibitors. You want to be careful to not get it into the guts of electrical components, but for cleaning surface corrosion can do wonders. The various metal "jellies" are similar, just in gel form which may be easier to control. However, if you need to loosen components with little clearance, the liquid works better.