Letter 11080

Boric acid level in a sulfamate nickel bath 

I hang anode bags full of boric acid in my sulfamate nickel plating baths, and I find myself refilling them all the time. Can I dissolve too much boric acid in the bath?

Michael Brewington
plating shop. - Salisbury, MD, USA

You can not add too much. A saturated solution is optimum.

The boric in the bag is subject to a significant agitation and saturates the bath at working temp. When you shut down, agitation and temperature both drop and the saturated solution becomes supersaturated and precipitates to the bottom of the tank. On Monday, the process starts over.

You very probably have a thick to very thick layer of boric on the bottom of the tank.

James Watts
- Navarre, Florida

Well, you can't dissolve more boric acid than the solubility limit. But the problem is that if your 140 degree tank drops to a lower temperature, boric acid will precipitate and you will have particles that don't readily dissolve, and that will cause you problems.

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

Michael, boric acid should be maintained at an optimum level, in decorative nickel, 6 to 8 oz/gal. Prevents burning and pitting just to name a couple. Using an anode bag to maintain boric in the bath has been around forever. Yes it is consumed during plating. Don't you or a vendor run routine analysis on a regular basis?

Bill Hemp
tech svc. w/ chemical supplier - Grand Rapids, Michigan

Hanging a bag of boric acid in the tank is common. You want the bath to be at or near saturation. The only time you could get excessive boric in the bath would be if the temperature was excessive.

James Totter, CEF - Tallahassee, Florida

Michael,

I think that you should analyze for boric acid and make additions based upon the analysis. My experience is that boric should be maintained between 4 and 5 oz per gallon and NOT above that. The reason is that the boric is soluble at 140 deg F but the work piece entering the solution is only around 75 deg F. If the boric is going to crystallize out of solution, it is most likely to do so on the cold work piece and cause rough plating.

Pat Mentone St Paul, Minnesota

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