Dissolve aluminum from steel part

[Napier]

>I don’t think aluminium is particularly soluble in mercury.

Wait, wait - I heard somewhere that if you put liquid mercury in contact with aluminum and then scratch the aluminum under the mercury, the aluminum starts doing something - oxidizing, I think - that rapidly turns the whole (aluminum) part into powder. I think it had something to do with preventing the protective film mechanism from getting started.

[Squink]

@Napier

Wait, wait - I heard somewhere that if you put liquid mercury in contact with aluminum and then scratch the aluminum under the mercury, the aluminum starts doing something…

Mercury-aluminum amalgam

Normally pieces of aluminum aren’t very reactive because they are covered with a thin layer of inert aluminum oxide (Al2O3). The mercury in the solution allows this protective layer to be removed, then prevents its (otherwise very rapid) re-formation by creating a thin layer of mercury over the bare aluminum. The net result is similar to the mercury electrodes often used in electrochemistry, except instead of providing electrons from an electrical supply they are provided by the aluminum (which becomes oxidized in the process.) The reaction that occurs at the surface of the amalgam may actually be a hydrogenation rather than a reduction.

The presence of water in the solution is reportedly helpful (even necessary); the electron rich amalgam will reduce water to hydroxide, creating aluminum hydroxide (Al(OH)3) and hydrogen gas (H2).

Sodium hydroxide or ammonia accomplish the same reaction without using nasty, toxic mercury.

[Osip]

@Mangetout

I don’t think aluminium is particularly soluble in mercury.

Dude, trust me is can be nasty. There is a very good reason Mercury in thermometers are not allowed on airplanes.

[WarmNPrickly]

Sodium hydroxide or ammonia accomplish the same reaction without using nasty, toxic mercury.

Amen. We don’t need to kill anyone. Stay away from the mercury. Mercury (0) is not too bad, but you start doing Ox/Redox type stuff around it, you don’t know what form you might end up with. Anything other than mercury (0) is deadly. Besides, you would need a significant quantity to do anything significant, and I don’t know who would supply it to you.