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topic 9943

Zinc and yellow passivate composition


I have a customer that has asked the composition of zinc plate and passivate (needed for new EEC end of life directive for cars). The zinc is 25 microns thick with a standard yellow passivate (from a simple dichromate/sulfuric acid system). What I require is the % of chrome likley to be in the zinc.

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England


Why don't you process sample parts, strip the chromate film and analyze the strip solution for Chromium using an AA or ICP. Note: I am talking about chromium contained in the conversion coating, there is no chromium actually in the zinc.

Gene Packman
process supplier - Great Neck, New York


I believe you are actually looking for the amount of hexavalent chromium in the chromate conversion and this should not be done by striping and digesting the resultant solution in an acid as it will convert all the chromium to hexavalent. I believe there are leach procedures using DI water or artificial perspiration and then analysis for hexavalent chromium only (no acid digestion). You should get the specification they are referring to for exact details.

Tim Denhof
- Chicago, Illinois


As they say of wisdom seek and yea shall find. I have found the answer to the question in ISO 3613 [link by ed. to spec at TechStreet]

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England

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