More on Iron Phosphate over Zinc


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Q. I have a comment regarding a question in the May issue about delaminating on zinc substrates. Iron phosphates are very capable of providing good “morphology” and surface conditioning on zinc (nonferrous) alloy if fluoride is added to the bath. This is a standard and customary protocol requiring typically less than 0.1% F. Also, zirconium nanotechnology is capable of producing coatings on zinc without fluoride. The environmental considerations of zinc make using it extremely difficult for most customers. M.M.


A. In the May 2008 Painting Clinic question, titled “Paint Peeling from Zinc Surfaces,” both J.P. and V.C. had paint adhesion problems on zinc surfaces pretreated using iron phosphates. J.P. is using galvaneal treated steel and V.C. is using zinc-plated steel. In my answers, I told J.P. to either pretreat with zinc phosphate or use already pretreated galvaneal steel. I told V.C. to use a zinc phosphate. I did mention that certain iron phosphates will successfully pretreat zinc surfaces, but I may not have stressed that point strongly enough. I don’t know about them providing “morphology,” but I do know they will provide a paintable surface. It is unfortunate that zinc phosphates are not as environmentally friendly as iron phosphates. I hope this does not cause their extinction.

My last statement reminds me of a quote by Waldemar Kaempffert, who said, “This age of power is the age of steel. Age of rust would be a better designation. If it were not for our paints and protective coatings, nothing would be left of this machine civilization a hundred years hence.” With the extinction of zinc phosphates, the “would” might be changed to “will.”


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