HOME FAQs BOOKS JOBS: Help Wanted Suggestions you are here: Hotline/Forum => Letter 42029

Can trivalent chromate finishes oxidize to hexavalent?

++++++

I have been told, from certain suppliers, that the trivalent chromate as applied to a product can oxidize over a period of time to a hexavalent condition. If this is true, under what conditions does this occur?

Gary Hein
job shop plating - Santa Fe Springs, California, USA

++++++

Not spontaneously.
It may occur under some oxidizing conditions:
Alkaline oxidation with hypochlorite, ozone, permanganate or peroxide.

The presence of chlorine in oxidizing flames can lead to formation of the oxychloride CrO₂Cl₂(g) in welding fumes; one reason for OSHA's crackdown on hex. Cr.

"A Cl₂ [Cl-sub2, free chlorine] residual in a drinking water distribution system may oxidize any soluble Cr(III) to Cr(VI) because of the long contact time"
-- 'Chromium Redox Chemistry in Drinking Water Systems,' Han Lai and Laurie S. McNeill, J. Envir. Engrg., Vol. 132, pp. 842-851 (August 2006).

Ken Vlach
- Goleta, California

ANSWER or FOLLOW UP POST an unrelated QUESTION HOT Topics

Disclaimer: It is not possible to diagnose a finishing problem or the hazards of an operation via these pages. All information
presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The
internet is largely anonymous; some names may be fictitious and some recommendations may be deliberately harmful.

If you are seeking a product or service related to metal finishing, please check these Directories: