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Hexavalent Chromium Level in Passivation after Bleaching

2003

Dear All,

Just looking for confirmation, if I have a zinc alloy casting which is colour passivated yellow, which is then bleach sealed is the level of hexavalent chromium still the same after the bleaching process. I am trying to estimate the amount of hexavalent chromium on our parts.

Regards,

Chettan Karsan
- Newmarket, England

i don't really know much about the passivation process but I do know hexavalent chrome turns to trivalent at 500 degrees.

doug samson
- greenwood, South Carolina
November 14, 2009

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Hi. I can't comment on Doug's response, but back to the original question, no, the level of hexavalent chromium is not the same after bleaching.

The bleaching process is not chlorine bleach, it's just hot water that leaches out a good portion of the chromate. The fainter color of the parts is because there is less yellow hexavalent chromate on them after it's been leached out.

Note, though, that bleached/leached chromate will probably not pass RoHS requirements, which are for very little hex chrome.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
November 14, 2009