Metal finishing Q&As since 1989

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citric acid Passivation

I need to passivate some 316SS parts and was told by a vendor that citric acid was best for my application. I did not however get a typical concentration for the citric bath. (i.e. 3 Molar)

Dan C [last name deleted for privacy by Editor]
- Beverly, Massachusetts
2001

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citric acid is the base, but there is more to it than just citric acid , Dan, and I believe that citric acid formulations today are still proprietary rather than published like nitric acid formulations. In other words, I think you buy a proprietary product or license it. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2001

Dan:

Formulations have been developed which make citric acid not only a replacement for nitric acid, but an improvement over nitric acid for most passivation applications. These formulations are tailored for the various jobs being done, and to optimize the cost and passivation results; all without the hazards of nitric. You can visit our web page to learn about it, or call us to discuss your exact application.

Regards,

Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois

2001

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2002

Passivation for Stainless Steel Tanks

1) Cleaning:

Make sure the equipment is clean prior to performing the passivation.

2) Passivation:

Fill up the tank with hot city water or Hot D.I water, to a level that is enough to cover the stainless steel surface that needs to be passivated.

Record the amount of water: ________________kg.

Need to make 6.67% concentration of citric acid by using following equation: The quantity of citric acid to be used is:

(x/93.33%) -x = ___________kg where x= amount of water from above

Turn mixer on and add citric acid to the equipment and mix until uniform.

Heat the citric solution to 50-72°C.

When temperature reaches 50-72°C, allow the solution to contact the surfaces for 10 minutes.

Cool citric solution to 35-40°C.

Neutralize citric solution to pH = 5 - 6.8 with NaOH . Then empty citric solution to the drain. This action will require the use of an additional vessel.

_____(amount of citric acid used) x 0.5 = ______ (amount of NaOH needed to neutralize citric acid solution.)

Rinse the equipment thoroughly with hot D.I water.

Beige J [last name deleted for privacy by Editor]
- Roanoke, Virginia, U.S.A.

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I have stainless steel parts that I need to passivate. I currently have citric acid in a fine powder form (16 oz) I received from a reputable chemical company and need to know the exact process to passivate a part no bigger than a standard 9-volt battery. I am not interested in setting up a passivation line, but just doing some preliminary tests.

Thanks,

John Woodall
Laser engraver - Indianapolis, Indiana, US
2007