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Mixing sodium di-chromate in passivation  

September 16, 2008

For types 1, 2 and 3 passivation, what should the concentration of sodium di-chromate should be in the bath? Is it the same concentration for all three types or different?

How many pounds per 100 gallons for the concentration?

Thanks everyone!

Mike Davis
shop employee - Kalispell, Montana, USA

Hi, Mike. It's probably about one-half percent to one or two percent, with the higher concentration being for the deeply colored chromates and the lower concentration being for the clearer chromates. There are also usually accelerators present and fluorides sometimes as well. You can find something about the formulation of chromate conversion coatings by going back to the mid-fifties when the basic R&D work was published, but these products have been primarily proprietary for decades now. Is there a reason you are trying to use home-brew?

Regards,

Ted Mooney, P.E.  finishing.com Brick, New Jersey

Which specification are you referring to? ASTM? Is this for stainless steel passivation or Al chromate conversion?

Terry Lycans
- Dayton, OH, USA