Alternatives to Divercoat 7T
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My company is currently seeking an alternative to Divercoat 7T. We maintain Alodine tanks for conversion coating aluminum. The MSDS of the last shipment of 7T lists it as containing cyanide. In an effort to minimize the severity of our waste streams, I am searching for an alternative chromate conversion coat for aluminum. The local sales representative recommends Novacoat 1100 by Novamax due to its lack of cyanide. Any comments about the effectiveness of Novacoat 1100 or any alternative recommendation as a conversion coat?
Thanks in advanceAlan Morton
Hello, Alan. We don't want to compare one proprietary to another on this forum, but we do talk about generic issues like the cyanide content of chromates. Chalk the following up as urban legend, but my understanding is that cyanide is an accelerator that allows the conversion coating process to proceed much faster. If I'm right, as long as longer immersion times won't mess up your production, you can probably move towards cyanide-free chromate conversion coating. Good luck.
Ted Mooney, P.E.
Pine Beach, New Jersey
The cyanide in products such as the one you are using is a ferricyanide. It is a bound cyanide. If your pretreatment standards list cyanide as "free", you are O.K. If it lists total cyanide the ferricyanides are included.
A product, Chromicoat L-25 with T3 as an additive is used at 5% heated 90-110. It is not as user friendly as the ferricyanides but works well.Dan Zinman
What does 'not as user-friendly' mean in this context, Dan? That it is more time-consuming to control and keep in balance than ferricyanide products?
Ted Mooney, P.E.
Pine Beach, New Jersey
This is a little fuzzy in my mind, but I heard that the ferricyanide had been taken out of conversion coatings for aluminum quite a while ago. An artifact of the use of ferricyanide in this product is that the sludge produced from conversion coatings on aluminum is still listed as one which cannot be landfilled. But I guess that the death of ferricyanide in aluminum conversion coatings has been greatly exaggerated.
I would definitely spend the time to find a supplier who offers a non-cyanide formulation, I believe you are using an obsolete product. It would be worth the effort, I think.
We are currently using Oakite Chromicoat L25. They claim it to be cyanide free. Immersion times run well under 5 minutes. We are working to Mil-C-5541 [link by ed. to spec at TechStreet] CL 3 and 1A. For what it's worth our lab reports on our pre-treated wastewater show almost no cyanide or non-detectable amounts. This could be coming from our deoxidizer solution as the only chemical listed on the MSDS is potassium ferrocyanide. A rep once told me that the L25 makeup solution doesn't contain cyanide but the replenishing solution T3 does.Scott Hearn
- Oklahoma City, Oklahoma U.S.
We have used Novacoat 1100 at our facility here in Marietta, Georgia since 1993 with excellent results and currently maintain a 22,000 gallon tank on our main line and a few smaller tanks under 2,000 gallons. This product contains no cyanide and is accelerated with fluoride. It produces a deep, golden, iridescent color and provides a very good substrate for subsequent waterborne epoxy primer application. One advantage we like is the fact that it is approved in the QPL for QPL-81706 [link by ed. to spec at TechStreet] for both Class 1A and Class 3 applications. Unfortunately, I've heard that Henkel, the new owner of the former Novamax, is looking to phase this product out.Ken Danals
- Marietta, Georgia
Ed. note: Thanks everyone. I think you have answered the technical questions well, and given Alan some direction. We should leave it as that, and reserve brand comparisons for private meetings with trusted associates.
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