Summary for sulfuric acid anodizing solution Discussion
Sulfuric acid anodizing solution is discussed mainly in terms of compliance and bath control, not a fixed drum-to-water recipe. In the 2022 exchange, Rachel and Ted advise Michael to redirect auditors toward the actual tank concentration, since the supplier’s drum strength can vary from 94% to 98% and still be acceptable if the bath is tested and meets MIL-A-8625 / MIL-PRF-8625 requirements. They recommend an SOP stating that after any addition, the tank must be tested for concentration before returning to process. Michael later says his quarterly tank analysis, including aluminum content, satisfied the auditors. In an older reply, Robert H. Probert notes that the basic bath is sulfuric acid and DI water, but the usable concentration depends on the process; he also says a small amount of dissolved aluminum is desirable when first making a bath and that bulk premixed solution is usually impractical because additions are normally made with straight sulfuric acid.
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Q. Hi, our Auditors wants to see the mixing ratio for sulfuric acid 98% and De-ionised water on the MIL-A-8625 / MIL-PRF-8625
[⇦ this spec on DLA] class 1 type 2 spec, however I went through the whole document and nowhere it states. Although our supplier gave us a document stating the ratio this is still not sufficient. Is there anywhere that we can reference the mixing ratio to the provided MIL spec for our auditors?
Michael van der Watt
– Western Cape
March 31, 2022
A. Hi Michael. I believe you are right that MIL-A-8625 does not specify the acid concentration or dissolved aluminum content or other parameters. However, I believe that it does say that *you* must do so :-)
Luck & Regards,
Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com – Pine Beach, New Jersey
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March 2022
A. Hi Michael,
Can you redirect your auditor to focus on actual concentration in the tank, which is more important for adherence to spec?
If your auditor asks for a “mix ratio” and your supplier gives you sulfuric anywhere between 94 and 98%, the drum strength is immaterial; as long as you prove tank concentration, you are conforming to specification.
Your SOP should state “when an addition is made, the tank shall be tested for concentration prior to being returned to process ” or something like that. Because if you formally state that requirement, you can take any concentration of drum acid you want, and as long as it gets tested and meets spec, you’re fine!
Rachel Mackintosh
Lab Rat / WWTF – Greenfield MA
May 12, 2022
Thank you Rachel and Ted, I send my tank analysis to our supplier once every 3 months and that was the actual document they were looking for to see if there was any addition and what the aluminium content is. Everything passed.
Michael Van der Watt [returning]
– Cape Town
May 12, 2022
! Great to hear! And if you ever feel like you might need to test it in house on the fly, like when you’re returning to service after a decant, there’s a 2 part titration including an aluminum correction posted on this site which is a nice tool to have in your toolbox, for when you simply can’t wait for lab results! It’s not as daunting as one would expect. Really one of the most straightforward tank tests.
Rachel Mackintosh
Lab Rat / WWTF – Greenfield MA
May 14, 2022
⇩ Similar, related, Q&As — oldest first ⇩
Q. Wondering if anyone knows of, or where I can find, the formulation for creating sulfuric acid anodizing solution. I would like to be able to mix this from raw ingredients to create bulk quantities. Must be able to plate AL parts to
AMS2471D, AMS2472C and
MIL-A-8625 / MIL-PRF-8625
[⇦ this spec on DLA]F,type II specs. Need to keep costs and turn times down.
Thanks,
Andrew Wong
– Richmond, B.C. Canada
2002
 | A. It is just sulfuric acid. Use Electronic Grade 66 baumé then make-up at 15%/wt=22 AV Ox/gal = 12 fluid ounces/gal = 165.3 grams/liter. That is it. You can use an additive available from about 7 vendors.
2002 A. Andrew, I can’t imagine why you’d want to create bulk solutions..but, in any case..the most basic solution is, of course, sulfuric acid, and DI water…there are many different concentrations, that will serve different purposes. There are also additives that allow one to “hardcoat” at elevated temperatures. Also, a small amount of dissolved Al (2 gr/litre should suffice) is also desirable when first making a bath. Are you thinking of marketing such solutions? I really wouldn’t think there would be much of a market for this, as its very simple to do…and I, for one, wouldn’t pay the extra cost to have someone else make my bath. A bulk solution also, wouldn’t be practical for bath additions, as the titration is very simple, and you wouldn’t be adding dilute solution to your bath, just the straight sulfuric.
A. Metal Finishing Hand Book among many books. Chris Snyder |
