letter 20093

Hexavalent Chromium Level in Passivation after Bleaching  

+++

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 dont really know much about the passivation process but I do know hexavalent chrome turns to triavalent at 500 degrees.

doug samson
- greenwood, South Carolina

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.  finishing.com Brick, New Jersey