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Limits on Pb and Sb contamination of Cr passivation solution

October 13, 2010

Galvanizing baths can have Pb and Sb added to give spangled appearance. They can carry over to the Cr bath used to passivate or pre-treat the Zn coating before painting. Does anyone know the acceptable limits of Pb and Cr in Cr post-treatments and their effects on passivation?

Frank Goodwin
Researcher - Durham, North Carolina, USA

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November 16, 2010

Hey Frank,

I doubt that antimony or lead has any effect on a hex chrome quench. The pH is extremely critical and eventually zinc build-up can be a problem. Acetate anion improves a hex chrome quench for zinc. Properly formulated and maintained a hex chrome quench can last several years, whereas a high pH can shut down a hex chrome quench in a few months.

Regards,

Dr. Thomas H. Cook
Galvanizing Consultant - Hot Springs, South Dakota, USA