Aluminum oxide - remove or leave???

I am no metalurgist, so I am throwing this out there for all the experts on MP.

All of my non-anodized carabiners have a layer of Aluminum Oxide (AO) on them. Some date back to the early 90's, some are practically new. The stuff is annoying because it coats your hands and gear with black shite. Same can be said for other aluminum gear I guess, but I am specifically talking about biners.

Is it OK to remove this with a metal polish? Just wipe it down with a damp rag? Acetone? Am I crazy or anal retentive to want clean gear?

Like I said, some of it is almost 20 yrs old, Petzl spirits and BD Light D's mostly.

It came up because I have a new rope, and the dark smearing from tying into the master biner with a clove hitch left a dark mark on the rope.

if you clean it, it will come back over time. i am no expert, but aluminum oxidation is a naturally occurring protective layer (self renewing) and gives the aluminum alloy some corrosion resistance.

youre not crazy. i agree that dirty black ropes are a pet peeve.
anodized biners help keep it off your hands. but after a while where the rope wears, will also get an oxide layer and dirty the ropes...

As above, all aluminum will naturally develop a coating of aluminum oxide on it when exposed to air. Anodizing is simply an artificially thick layer of aluminum oxide created on the material, usually for cosmetic or wear resistance. So no, cleaning it off won't help anything since it'll be back fairly quick.

BTW, anodized gear will have the same problem once the anodized layer wears through (which is usually obvious as that section will lose its color).

-a.

Both WiledHorse and Aric are correct. The natural Al-ox layer is only a few nanometers thick, and takes a fraction of a second to form. If you have visible crud on your biners it is probably dirt.

For those that are interested, the aluminum oxide layer is known as a metal passivator. And Aric is correct in that anodization is simply an artificial thickening of that layer. Also, the color is from a dye that is added when the pores in the passivation layer are sealed - it is only on the outer part of the protective layer, so just because your rope has worn through the color doesn't mean the anodization layer is gone yet.

And one more random tidbit about aluminum: though I doubt anyone has old thermometers anymore, if any mercury EVER comes into contact with aluminum climbing gear, throw it all away immediately.

And Chris is correct that Wiledhorse and I are correct. :-)

...Although I might argue that the color is added prior to sealing, but that's getting picky about the anodizing process.... ;-)

Chris Drover wrote:And one more random tidbit about aluminum: though I doubt anyone has old thermometers anymore, if any mercury EVER comes into contact with aluminum climbing gear, throw it all away immediately.

Jon H wrote: Interesting - can you expand on that? Feel free to take the answer to a Gen Chem 102 level. Go above that however, and I'll probably lose you.