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citric acid passivation process for medical device

2007

The company I am currently working for has been asked to passivate a 303 medical device part using citric acid . I have found a great deal of information concerning the use of citric vs. nitric but am worried that it isn't accepted in the medical community. Much of the research I have done shows that it is a cost effective, environmentally friendly and safer then nitric for general purposes.

I need to have a fail rate less then .5% in a salt fog, and the part has no small tubing or holes for chemistry to get trapped. It is absolutely crucial that the surface has no contamination after passivation, and can't alter the conductivity of the part since it is used as a contact for a battery.

Any information would be greatly appreciated.

Brandon Brandt
Process Engineer - Minneapolis, Minnesota, USA

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The citric acid process only removes iron from the surface. It does not apply a controlled oxide to the exposed nickel.
On 304, which is barely "stainless", I would not recommend this process.

Nitric Acid does two things. (1) It removes free iron from the surface and (2) it applies a controlled oxide to the nickel which inhibits further Uncontolled oxidation.

Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

2007

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303 SS may not be suitable for medical devices exposed to body fluids or harsh sterilization techniques. But, problems are mostly due to cheaper material with uncontrolled sulfide morphology. To meet your requirements, use a premium grade such as Project 70+ from Carpenter Technology and follow their recommendations for passivation of the free-machining 303 SS. Both nitric & citric acid procedures are given at
http://www.cartech.com/machining_zone/citric_pass.html

In either case, follow the alkaline-acid passivation-alkaline procedure. If using nitric acid, letter 35096 recommends using Type VIII rather than the more common Type II passivation solution (QQ-P-35C designations). Note: Type VIII is called Nitric 4 in ASTM A967.

Stellar Solutions [a finishing.com supporting advertiser] has instructions and solutions for citric acid passivation.

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.
2007