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White 'dusting' on nitric acid passivated 304L parts



January 12, 2012

Q. I have some 304L stainless parts treated in ASTM A967 [affil. link] Nitric 2 bath. The parts are precleaned in a Chemetall Oakite Aluminum Cleaner 166. When the parts are done and dry, a light white coating is left on some of the parts. I would like to stress that not all parts have this light coating. It almost looks like dust that you could wipe off. It is something you could take off with a scotch brite pad. My metal finisher says this could be the result of a slightly porous material.

What could this be and is this something that I should be worried about?

Thanks a lot!
Jon

Jon Danielson
engineer - Loveland, Colorado



January 13, 2012

Jon

An aluminum soap may or may not be adequate for cleaning your parts, depending on how soiled they are.

I would try an ultrasonic cleaning prior to passivation as a first step. You could always try another supplier. If it is the material, I would expect all the parts to have the same appearance.

Willie Alexander
- Colorado Springs, Colorado


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