[conorh95]

Hi

So, I'm not really a chemist (only made an account to get this question answered) - I have an aluminium bicycle seatpost completely stuck to a steel frame, presumably due to oxidisation. If I pour some soda crystals  (not sure if you have them in the states, it's sodium carbonate decahydrate) and boiling water down the tube, will that eat away the aluminium oxide without damaging the steel?

Edit: I'm not looking to use the seatpost again, so it doesn't mattered if it gets destroyed
Thanks

[Borek]

If anything, I would use much stronger alkali (just NaOH - sodium hydroxide). Sodium carbonate is alkaline, but IMHO not strong enough to dissolve aluminum fast enough. Trick is, you want the reaction to be as fast as possible, as any contact with water and air oxygen will corrode the steel frame as well (especially in the presence of a highly conductive solution).

[billnotgatez]

Just to underscore safety

Hot caustic soda is intense

Some thoughts
wear protective gear like goggles etc.
Do this outside and stand upwind
Have lots of plain water on hand like a garden hose with squeeze nozzle
Do not splash yourself or others
Be prepared to deal with the disposal of the caustic stuff

[Arkcon]

If you want to augment brute force separation with some sort of reactant, I'd choose Naval jelly -- a gelled preparation of phosphoric acid.  You can smear it at the joint, it will cling and attack the more active metals and the oxides, but not corrode steel.