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Ask the Expert Question-and-Answer Archive

by Ron Joseph

February, 2005

Foaming of Phosphate Surface Pretreatment Bath

Q. I am using Oakite Gardobond S5206 in stage # 1 (140F). The carry over goes to stage #2 (rinsing). Keeps TDS to rise and as soon as fresh water is added, it starts foaming madly. Can you please suggest some solution. I have a few things in mind.

1. Heat stage # 2 through immersion heater.
2. Use some kind of non-silicon based de-foamer.
3. OR something else..?

Please advise. I shall be very thankful for your guidance.

A. It sounds to me that the addition of non-silicone defoamer might be the best solution, but I would ask the folks at Oakite for their solution. They might want to test the chemistry of the rinse tank before and after you add the fresh water. My guess is that the sudden change in pH is the problem and you need something to stabilize the pH or act as a buffer.

Rather than do this by trial and error (adding the defoamer) I would first get the folks at Oakite to respond to your problem. I would hate for you to destabilize your rinse stage and the third stage by adding a chemical without knowing how it will affect the remainder of your system.

Best wishes,

Ron Joseph

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