We have some 316 stainless steel parts that will come into contact with phosphoric acid for an undefined length of time.
For compatibility, i have been told that passivation by nitric acid is required. I have also been told that the stainless steel parts have been passified with citric acid.
Is there any difference between passivation with either acid or is it only the 'weak acid' chemical property that is required?
Thanks
Dear Dr. Chris Todd,
citric acid (more environmental friendly than nitric acid) passivates surfaces of stainless steel producing higher Fe/Cr and higher Fe ox/Cr ox ratios than nitric acid, electro-polishing, and a sequestering agent. Low potential values indicate the highest surface resistance, thus citric acid produces most electrically resistant surface.
For more details, please see the source at: https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110001362.pdf
Best regards, Pierluigi Traverso
Chris
I also confirm with Pierluigi that citric acid is more beneficial in all aspects of passivation of SS, especially it is a green passivation of stainless steel and is more friendly with respect to work with.
Both acids provide effective passivation of stainless steel and details can be found in ASTM A767 and AMS2700
Dr. K
used citric acid for for passivation of 316 stainless steel, the passive region is wider than nitric acid (the result from potentiodynamic
polarization experiment)
- Badges
- Science topic
- Similar topics
- Physical Sciences
- Materials Science
- Materials
- Inorganic Materials
- Metals
- Alloys
- Steel