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I'm looking for a wet-etchant to remove aluminum oxide created by anodizing, but not etch the unoxidized metal (with greater than 10:1 selectivity)

I know about chromium(IV) oxide and fluorine-based etchants, but those are problematic for safety and disposal. Are there other etchants? It can be an acid or a base.

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  • $\begingroup$ Did you actually manage to pull this off? Because etching isn't as hard as preventing a new layer of oxide forming in seconds in air... You'd basically have to work under an inert gas atmosphere, whatever is that you're trying to do thereafter. A more typical approach is to nickel coat the Al sae.org/publications/technical-papers/content/880446 $\endgroup$
    – Fizz
    Feb 6 '21 at 9:15
  • $\begingroup$ Fizz - no, I have not. Closest thing I found was zincating, but of course that does not satisfy the other constraints (no etch of other metals.) The problem is the raw material comes with an oxide. $\endgroup$
    – Richold
    Feb 6 '21 at 18:49
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In Fabrication of Microstructures by Wet Etching of Anodic Aluminum Oxide Substrates Chem. Mater. 2005, 17, 4049-4052,

5% phosphoric acid is used and is selective relative to aluminum, but you need to check how it would do with respect to the other metals you mention

Finally, the AAO substrate was wet-etched in a 5 wt % H3PO4 solution at 20 °C for 8 h

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Alumina can be dissolved in sodium carbonate. But it would expose the bare metal to aerobic corrosion.

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  • $\begingroup$ While I do not agree that it does not attempt to answer the question, at the moment this reads more like a comment than an actual answer - could you elaborate a little more, perhaps include a link to a general procedure or outline it. $\endgroup$ Apr 13 '16 at 5:16

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