Letter 41067

Hexavalent Chromium, how do I test for it on fasteners  

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I am a fastener distributor in Chicago, IL & with the evergrowing need to have parts be ROHS Compliant, I would like to either create or purchase a test kit for the detection of hexavalent chromium on zinc & zinc/aluminum alloy coated steel. Do you know of any test methods currently out there???

Tony Keas
hardware & electronics - Chicago, IL

Rohs compliance can be tested by following a procedure set out in GM spec 3044W. You can probably buy the test kit from a local company, Kocour. Be advised, that using this test some products can give a false positive. The more accurate method is to send a sample of the batch to a lab for testing using an ICP. Generally, most end users rely on a certificaton from the plater stating that the finish is RoHS, WEE or ELV compliant. The alternative statement the finisher might make is that the part does not contain hexavalent chromium.

Gene Packman
- Great Neck, NY

I want to know by looking on to any component how we can understand that whethet it is Trivalent Chrome or Hexavalent Chrome or If any other verificaion method available for the same.

Navin Sobhani
controls & switchgear - Noida, India

Another option is to try portable x-ray fluorescence (XRF) for your fasteners that are out in the shop. But keep in mind that neither XRF nor ICP (in the lab) can distinguish between trivalent and hexavalent Cr coatings. If you know what else is in the Cr coating you might be able to look for that species, but that is an indirect way of doing things.

Terry Tomt
- Auburn, WA

Cr 6+ can reduce sodium thiosulfate solution (iodometery).But Cr 3+ can not reduce above solution.

Garshasb Mir
- Esfahan, Iran

The only method which can tell the difference between Cr6 or Cr3, is by an indicator named diphenyl carbazide. The point is that it has to be freshly made up.

Sara Michaeli     chemical process supplier Israel

Sara,
The method you refer to will give a false positive in the prescence of iron, cadmium, zinc or several aldehyde compounds. That is the reason why the ICP method is suggested. The testing is done similar to waste water where trivalent and hexavalent chromium are seperated. The protocol for this test is spelled out in the specs from National Semiconductor among others.

Gene Packman
- Great Neck, NY

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