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Anodic Seal

I am running a nitric based anodizing bath with a hot deionized seal. I have to work within the Dehavland pps32.03 and Bell bps4001 specs. The problem I have is that the incoming water pH is between 6.8 and 7. The specs require a PH of 5 to 6.8 and my lab tests always come in around 7 - 8. How can I bring the PH down without going over the <=20ppm TDS requirement?

Steve Davis
Aerospace - Sidney, BC, Canada
2007

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First of three simultaneous responses -- 2007

I don't have the chromic acid anodizing specs. Perhaps, acetic acid ⇦ this on eBay or Amazon [affil links] (reagent grade) is allowed (doesn't count toward 20 ppm limit). Even if included in the 20 ppm limit, smaller pH adjustments are still possible.

To reduce the pH of DI water:
>From 8.0 to 6.0 requires 60 ppm acetic acid .
>From 8.0 to 6.5 requires 18.4 ppm acetic acid .
>From 7.5 to 6.5 requires 17.1 ppm acetic acid .

Ken Vlach [deceased]
- Goleta, California
Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work which the finishing world, and we at finishing.com, continue to benefit from.

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Second of three simultaneous responses -- 2007

Hi,

Control the pH especially to below 6 by acetic acid ; I don't think there will be any problem with the TDS.

Good luck.
Basu

Srimay Basu
- Dubai, U.A.E.

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Third of three simultaneous responses --

Is there really such a thing as nitric acid anodizing? You might try lowering the pH by using acetic acid . It is organic and might not show up as a TDS.

James Watts
- Navarre, Florida
2007