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Passivation using chromates

Q. I am an University student doing my project in Southern Pipe Industry(M) Sdn Bhd. Currently, our passivation process for our pipe is using chromate acid. Somehow, performance of chromate will highly affected by contamination of Zn in the bath. This Zn might dissolve from the galvanized pipe during the passivation process. Is there any advice on handling the problem of Zn contamination, or always maintain the chromate acid at 25% concentration. Currently, the method we are using is check the concentration based on its conductivity. But, this is not that accurate as the Zn in the bath will effect the conductivity as well.

Thanks.

Quah Ban Kheng
Tube Mill - Butterworth, Penang, Malaysia
2004

A. He, Quah. There is more to a solution for proper chromating of zinc than just the chromic acid. There are countless suppliers who offer proprietary chromating formulations that solve such problems as excessive zinc dissolution, and probably do it less expensively and with less environmental impact than straight chromic acid. Henkel, Macdermid, Atotech, Chemetall, Accu-Labs, Inc. [a finishing.com supporting advertiser], and CST Surtec are a few such suppliers.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2004

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