Need help on de-smutting of aluminum

A. Dear Mr. Thortan,

Maybe you can try this recipe: 50% nitric acid with 120 g/L ammonium bifluoride. I've had always good results with this mixture.

Kind regards,

A. You do not need ammonium bifluoride on wrought alloys like the 6000 alloy series (it will work, but you etch which leaves a light smut and also attacks the titanium racks).

At least 20 companies in the USA sell a proprietary deox like you describe which contains ferric sulphate and sulfuric acid. Some are listed on finishing.com

A. Dear Joe.
I asked same question myself last year. I inquired of some sources and searched some web sites and after it all I found a formula (not special) and I implemented it during process. There was no problem about quality of parts. So my formula (without nitric acid) for 6000 series:
- 180-200 gr/lt sulfuric acid
- 2% hydrogen peroxide (as an oxidizing agent)

You can try it.

Sincerely,

I saw your above post about using sulfuric acid with 2% hydrogen peroxide, but I didn't see how much of the 2% hydrogen peroxide you add?

Looking for a desmut alternative to nitric acid for use on 2024 aluminum.

Taylor
- Bend, Oregon
April 8, 2025

Tip: This forum was established to build camaraderie among enthusiasts through sharing tips, opinions, pics & personality.
The curator & some readers who publicly share their info will be less likely to engage with those who don't.

"Hydrogen Peroxide 12%"

on eBay or

Amazon

(affil links)

A. Hi Taylor,

We'll see if Alaattin responds, but I'm confident that he does not want you to add some quantity of weak 2% peroxide, but to add a quantity of peroxide sufficient to raise the peroxide concentration in the solution to 2% by weight.

Peroxide decomposes pretty quickly so you might contact a plating chemical supplier to investigate proprietary stabilized hydrogen peroxide ... but if you just want to give it a quick small scale trial, you can easily buy 12% peroxide ⇨ Luck & Regards,


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

A. Hi Aijazullah. pH is not a good way to determine whether the rinse will adversely affect the anodizing tank or not. A few drops of acid in very clean water will lower the pH to 4, whereas once the water accumulates a heavy dose of ions it takes quite a bit of acid to significantly change the pH.

As a thought experiment, imagine that you had a vat of strong caustic and you added sufficient acid (a lot of acid) to get the pH to 7 (neutral). It would take a huge amount of additional acid, not a few drops, to further lower the pH to 4.

An old rule of thumb is that figuring on between 500:1 and 1000:1 dilution in the rinse tank is a good starting point for experiments. The best way to decide when the rinse tank is too dirty is empirically with a conductivity meter. Although you probably can't determine from first principles how contaminated is too contaminated, with a little experience you'll know what conductivity is acceptable and what is excessive. Have you considered having 2 rinse tanks between the processes, which will both drastically cut the flow rate and eliminate your worries about the first rinse being too acidic. Good luck.

Regards,

A. I have been using hydrogen peroxide/sulfuric acid/nitric acid mixture as deox process over one year instead of licensed products. I certainly advise to use this mixture ... don't forget, hydrogen peroxide one of most powerful oxidizing agents as a chemical product. Try it and you will see good result.

Good luck.