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Ted Mooney, P.E. RET
Pine Beach, NJ
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for Metal Finishing since 1989
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Sulfuric Acid Anodize: Cl-, F-, Sulfide Limits
Q. Hello, I manage chemistries and solution testing for a finishing company. I am new to this industry (3 years experience with finishing solutions).
I was recently asked by a customer what our "limits for chlorides, sulfides, and fluorides" were for our Sulfuric Acid Anodizing. They did not have a tolerance limit themselves and I am wondering if anyone has a tolerance limit for these components in a solution and why. We have had 1000 ppm programmed into our LIMS system for several years, but have no notes as to why and what problems exceeding these limits could cause.
Our most recent results have given a maximum of 68.7 ppm for chlorides and 1.0 ppm fluorides. Sulfides are newly requested and no results as of yet. We use DI water in our anodizing line.
I do not know what is considered acceptable. Any information is greatly appreciated.
Thank You
- Erie Pennsylvania
September 1, 2021
A. Chlorides and Fluorides:
Sheasby/Pinner: 200 mg/L :to prevent pitting"
Arthur Brace:50 mg/L or you get white spots in the dye.
Boeing: 160 mg/L but they are never dyeing.
Reliable Dye suppliers:50 mg/L
Sulfides are not a common impurity in anodizing.
More impurity data is available in some books.
Robert H Probert
Robert H Probert Technical Services
Garner, North Carolina
September 7, 2021
Thank you kindly good sir.
Q. Is there an "easy" way to remove chlorides and fluorides from an SAA solution without decanting?
Again, thank you!
- Erie Pennsylvania
September 8, 2021
A. Hi Leslie. There is probably no practical way, but hopefully Robert will find time to follow up.
In case you read about it elsewhere though, there is an 'easy' way to remove chlorides from nearly any solution: add silver nitrate so that silver chloride precipitates ... but the economics of this are usually out of the question.
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
September 2021
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A. No economic way. First find out where the halogens came from: tap water, well water, some hard coat additives, other. Then, at the price of quality sulfuric acid, dump and recharge. To other readers who may be doing Type I Chromic anodizing, the chlorides will fizz off in time. Robert H Probert Robert H Probert Technical Services Garner, North Carolina September 8, 2021 September 8, 2021 Contaminants of the chemical solutions in a standard anodizing process are below; Anodizing Supervisor - TURKEY Sakarya |
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