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Citric Acid Passivation of Stainless Steel
Products Finishing, May 1999
The benefits of using Citric Acid for passivation.
Passivation of Stainless Steel
Products Finishing, November 1998
Though the author only describes passivation with nitric acid, he gives a good explanation of the process.
How To Passivate Stainless Steel Parts
Modern Machine Shop, October 2003
A good overview of passivation.