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Excessive Foaming of Black Oxide Bath

Q. Hello,

I operate a hot Black oxide operation and have noticed that the bath periodically tends to foam excessively when it reaches 292-293 degrees. We run at a 292 boiling point. When water is added (very slowly and carefully) this reaction also occurs. This problem seems to happen with no apparent contamination to the bath. (It has happened with new chemical and after desludging). When the bath starts foaming, the foam will rise until the heat source (electric) is shut off. Any suggestions would be appreciated.

Daniel Bianchino
shop employee - Albany, New Hampshire, USA
April 23, 2009

A. I have seen the problem that you are having. I have always attributed it to having burned the batch. Its caused by letting the salts get up around 330 degrees. You should always run 2 thermometers in your tank at all times. Never trust just one. Also always control the temperature of the salts with water never with heat. Some companies used to sell rejuvenators to reactivate the bath and I have tried them with very limited success. I have also tried to add new salt to the bath which for the most part was a waste of time. Now days if my bath goes to pot and starts to foam bad I just dump the whole works and start from scratch. I have also noticed that if you are using prilled fertilizer as a source for your Sodium Nitrate [affil links] you might notice a bit more foaming than you might see if you were using pure chemicals. If you are using electricity to heat your tank make certain that you heat the tanks slowly. Some heat sources such as cartridge heaters can pour out a heck of a pile of heat and can burn the solution during warm up.

Rod Henrickson
gunsmith - Edmonton, Alberta, Canada
April 26, 2009