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Is hexavalent chrome still hex chrome after it is plated on a part?





July 9, 2010

With all the new regulations regarding Hex Chrome I have been asked if the chrome that has been plated on our parts is hex chrome. we electroplate Steel Rods in Hexavalent chrome baths. I am not a chemist therefore, I don't have the proper answer but it is to my knowledge that the chrome left on the rod is elemental chrome. I am looking for a good scientific description of how the chrome is changed from Chrome6 to elemental chrome.

Lance Penfield
employee - N. Sioux City, South Dakota



July 9, 2010

Hi, Lance. Although the inner details of all of the complex intermediate reactions involved in chrome plating are the stuff of deep award-winning science papers, they can be skipped. Chromic acid (H2CrO4 or sometimes called CrO3) contains hexavalent chrome, Cr+6. The plating current adds 6 electrons per atom, and forms Cr+0 on the part. As long as the part is well rinsed (preferably in D.I. water), there is no hexavalent chrome in or on it.

Note: this explanation pertains to chrome plated parts. If you also have zinc plated parts or aluminum parts that are "chromate conversion coated", that would be a different story.

Regards,

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


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