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by Ron Joseph
August, 2006
Zinc Chromate vs. Zinc Phosphate Primers
Q: I would like to know the Key Performance Indicator and Key Technical Difference between Chlororubber Zinc Chromate and Chlororubber Zinc Phosphate Primer ?
A: I don't know whose coating you intend to use, but in general zinc chromate is a more robust and effective corrosion inhibitor for steel than zinc phosphate. Since many companies do not want to have chromates (hexavalent chromium Cr6+) on their sites on account of the potential carcinogenic health hazard to painters, they prefer to use alternatives such as zinc phosphate. Please refer to your vendor's technical data sheet to see the differences in performance.
Please do not confuse zinc phosphate as a pigment in primers with zinc phosphate in aqueous pretreatment systems. When comparing aqueous zinc phosphate pretreatment with iron phosphate, the zinc phosphate is the better corrosion preventive.
Best wishes,
Ron Joseph
A: Unfortunately I do not know the performance details as you have listed. For those you will need to contact the manufacturers of the chemicals, and you might write to Henkel Surface Technologies and/or Chemetall-Oakite.
Please scroll down for more answers:
Dear Dr. RoJo,
Let me first express my gratitude for your kind education here. Thank you, Sir.
Further to your kind response may I put some more queries before your good heart, Sir ? I believe you will not feel otherwise and will be highly awaiting for your kind guidances, Sir. Please ...
(Q1) I would like to know the Key Performance Indicators ( KPI) i.e. the comparative performance superiority betwen the two Primer types w.r.t. the following:
application under high Humidity ( let say above 80%)
application under ST2 prepared surface with distributed Rust
application under acidic fumes environment
application under alkaline fumes environment
application under saline environment as in coastal region
application under Sulphurous environment
comparative effectiveness as moisture & air barrier
comparative effectiveness under monsoon weather
(Q2) Few literature states that ZINC CHROMATE is a Rust Inhibitive Primer but ZINC PHOSPHATE is not a Rust Inhibitive Primer - Is it correct ? When zinc phosphate is used in a primer I believe that it is a corrosion inhibitor. But in most cases zinc phosphate is used in an aqueous solution and participates in an electrochemical process that essentially plates a zinc phosphate onto the surface. We call this a "conversion coating". When zinc phosphate is used in this manner it does not perform the same as zinc chromate. for more detailed information on corrosion inhibition versus conversion coatings refer to text books on corrosion that you can find in a technical library.
(Q3.) Between Alkyd based ZINC CHROMATE and Polyamide cured Epoxy based ZINC CHROMATE which one is superior w.r.t. the above KPI as in Q1 ? In general Epoxy coatings are more durable than alkyd coatings. It does not make a difference if the pigmentation comprises a zinc chromate or a zinc phosphate.
(Q4.) Between Alkyd based ZINC PHOSPHATE and Polyamide cured Epoxy based ZINC PHOSPHATE which one is superior w.r.t. the above KPI as in Q1? In general Epoxy coatings are more durable than alkyd coatings. It does not make a difference if the pigmentation comprises a zinc chromate or a zinc phosphate.
(Q5.) Any other advises, Sir. You haven't told me what you are trying to accomplish? Why do you need all this information? Are you making a decision about the type of primer you should use on a project?
I will be highly awaiting for your valued responses, Sir
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