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Alodine/Iridite Issues

2004

Our company has an Alodine/iridite process for corrosion protection of 2024, 6061, and 7075. Our process setup appears a little different than most that I have researched. Almost all of the parts are cleaned in acetone ⇦ this on eBay or Amazon [affil links] Warning! highly Flammable! , rinsed, phosphoric/hydrofluoric acid cleaning, rinsed, and then Alodined, rinsed, and dried.

The problem lies in that the 6061 turns black in the phosphoric/hydrofluoric acid bath. To remove the black material we use chromic/sulfuric acid which works great. I have tried a nitric/fluoric acid which seems to work okay but if not rinsed almost immediately, the black material reforms. I am trying to reduce chromium in the wastewater and the hope is to get rid of the chromic/sulfuric acid. Any insight? Additionally, would there be any benefit to going to a caustic bath for cleaning and then nitric/hydrofluoric bath thus replacing the acetone and phosphoric/fluoric acid?

Jim Rabideau
Environmental Engineer - Peshtigo, Wisconsin, USA

Jim,

You may want to try a 50% nitric dip as a desmutter it will be less aggressive and should give you the results you are looking for.

Good luck,

Tim Palmatier
- Binghamton, New York
2004

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Not intending to derail the other conversation, but I was looking to hear from someone like you who used 50% nitric as a desmutter to ask if you have any experience with it for 7075. We are having adhesion problems with a type II coating for a super-clean super-critical space component; while there are (as always) a host of theories, one theory is that the adhesion may be improvable by insisting on this as the desmutter in lieu of various other formulations used by several shops.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

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2004

Mr. Rabideau,

Consider one of the following (safer) chemicals for deoxidizing:

1) 20-30% by volume nitric acid
2) 60g/L sodium dichromate, 139mL/L sulfuric acid

in place of the phosphoric/HF you currently use.

Best Wishes,

Mary Cera
- Oklahoma City, Oklahoma