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Passivation with phosphoric acid [India] 

August 26, 2008

For how much time SS should be dipped in phosphoric acid for complete removal of rust?
What are the other solutions for passivation of SS?

Deepak Kamble
product designer - Pune, Maharashtra, India

Hi, Deepak. I have not heard of phosphoric acid for rust removal. Phosphoric acid will convert red rust to black rust, but I do not believe it will dissolve iron, which is necessary for passivation. The two common acids for this are nitric and citric. See ASTM A-967 [link is to spec at TechStreet]

Regards,

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Deepak,
The time required to remove rust is going to depend on how thick the rust was to begin with, so basically it takes as long as it takes.
While phosphoric is a decent way to remove rust, as Ted points out it will not passivate stainless.

Ray Kremer Stellar Solutions, Inc. Algonquin, IL, USA