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Is trivalent chromating a billion dollar farce?
by Ted Mooney

Drop whatever you are doing and read "Unexpected Results from Corrosion Testing of Trivalent Passivates" by Tom Rochester and Zachary W. Kennedy in the Oct. 2007 issue of Plating & Surface Finishing.

This may be the most important surface finishing paper of the decade. -- Ted

Mukund Shinde
Shinde Chemicals Pvt Ltd - Mumbai, Maharashtra, India

Mr.Mooney,
I think you are one of the few people in the industry who understands the surface finishing aspect of chromate conversion coatings. In terms of trivalent coatings most of them do not provide adequate corrosion resistance to zinc plated surfaces which may be virtually a known and accepted fact throughout the plating industry. We have been in the industry for 30+ years, my personal experince being 15 years (I started at a early age of 17 in the industry) and know the importance of a good chromate passivation.

Though there are claims from various formulators to provide trivalent chromates which provide 100+ hours of corrosion resistance we desist from making such a claim. The best life we have observed from testing all the materials available is about 80+ hours, that too with a good organic top coat. I tend to agree with your point of view. For me on a personal front, although I agree it's toxic and environmentally hazardous when introduced in the environment, hexa chrome remains plated zinc's best friend. Parting note is that untreated trivalent chromium is almost as hazardous as hexa chrome. Thank you for beginning of a worthwhile discussion. -- Mukund, Nov. 11, 2007

 

Thank you, Mukund, but I am not a chemist , and do not actually have the deep understanding of trivalent chromating that you credit me with, just an ear to the ground. Please listen to our Podcast Interview with Tom Rochester on the subject. -- Ted

Update
by Ted Mooney

Please see letter 47049, which includes a reply by Eric Olander of EPI, with details about a Sur/Fin paper/session addressing the issue (I infer that this paper will rebut the theory of spontaneous conversion to hexavalent), The same letter also mentions an article by John Bibber of Sanchem which includes photos and test results supporting the conversion to hexavalent -- Ted

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