The authoritative public forum
  for Metal Finishing since 1989
-----

Nitric acid in anodizing bath?

One small anodizing shop here in Costa Rica uses nitric acid and sulfuric acid on the anodizing bath. His sequence is cleaning, rinse, etching, rinse, anodizing,etc . I asked him what is the purpose of the nitric acid and he said me that nitric acid is a decapant.
Well I sure know that, but is it possible to de-smut while anodizing? I don't think so. Is it ok to leave the parts on the anodizing bath without applying current so that de-smutting occurs and then apply current to anodize? What consequences may this have on the final product?

Arnoldo Castro
- San José, Costa Rica
2006

---

Perhaps we might answer your questions by asking others.

Does the process anodise satisfactorily? Is the product from this particular anodiser OK? If so, the process would seem to be working fine.

Bill Reynolds [deceased]
consultant metallurgist - Ballarat, Victoria, Australia
We sadly relate the news that Bill passed away on Jan. 29, 2010.
2006

---

I am curious as to the contaminant growth in the Anodizing bath. after etching say 2XXX series aluminum.. where would all the copper etc. go? into the Anodizing solution..?

how high is the HNO3 concentration.. and does it affect the dissolution rate in the anodizing process.

Ryan Cook
Toccoa, Georgia
2006

Perhaps they were wrong. Weeks later they told me that the anodizing bath contains only dissolved sulfuric acid. No problem then, I guess. They might have read this thread.

Arnoldo Castro
- San José, CR
2006