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RoHS compliant black oxide alternative

I work for a motor manufacturer and am looking for a "blackening" corrosion proofing that is RoHS compliant and would be similar to black oxiding. I've heard that there is also a "trivalent black" chrome process and that this is RoHS compliant. What are the major differences between these two?

Zbigniew B [last name deleted for privacy by Editor]
Engineering - Chicago, Illinois, USA
2005

Hi, Zbigniew. Black oxiding should be RoHS compliant providing a chrome-bearing post dip is not used, and I don't think it often is. But black oxide offers little corrosion protection even when waxed or oiled, and none without it.

The "trivalent black" probably refers to a chromate conversion coating. This is used on top of zinc or zinc alloy electroplating; it's not a freestanding process for steel parts by itself. This was traditionally based on hexavalent chromium (not RoHS compliant), but conversion coatings based on trivalent chromium (which is RoHS compliant) are now widely available. Good luck.

Regards,

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
April 14, 2008