De-anodizing aluminium

The gear-wheel shown has previously been anodized. Now it has been dipped in NaOH for a few minutes, and the anodization was thereby removed. About 25um of the surface has been removed during the treatment. The dull appearance shows that the surface is porous. By scraping with a knife, the surface becomes glossy, as demonstrated in a corner. For obtaining a surface with low outgassing, the NaOH treatment should be followed by ball-blasting or another polishing method. For comparison, a ball-blasted circular plate and a bare aluminium square plate are included.

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Last updated September 29, 1999 by norup@astro.ku.dk