David,

We use the following to remove Al2O3 from the Al substrate.  You may have to
experiment with the amount of time or some of the weights.  Otherwise this
works very well.  Hope this helps.

6.0  g. phosphoric acid            at 35-40 C.
1.55 g. chromium trioxide
100.0 ml water


Best regards,

Jon Hiller
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Jon M. Hiller
Argonne National Laboratory
Materials Science Division
Electron Microscopy Center
Tel: 630-252-9558
Fax: 630-252-4798
Email: hiller@anl.gov
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