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White rust on zinc plated parts with a trivalent chromate seal
We have a cast threaded nut which we send out for zinc plating and a subsequent trivalent chrome seal. the outside of the nut is "as cast" and has slight porosity.
we are experiencing a "white" powdery look. is this white rust?
end user - Pennsylvania
April 25, 2008
April 28, 2008
Hi, George. It's hard to say, but e-mailing a photo to mooney@finishing.com for posting here may help.
Regards,
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
Ted is available for instant help
or longer-term assistance.
April 28, 2008
You may be seeing white rust, which is the zinc corrosion product (hydrated zinc oxide, etc.). It is also quite likely that you are seeing a phenomenon called efflorescence, which is a reaction between a silicate polymer leachant-sealant with the carbon dioxide in the air. Not all sealants exhibit this phenomenon, but most do. Have your plater contact their supplier.
Tom Rochester
CTO - Jackson, Michigan, USA
Plating Systems & Technologies, Inc.
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