Q. I have green sludge collecting on the filters in my nickel plating bath. What is it, and what can I do to prevent this from happening in the future? T.E.
A. The sludge that you observe is nickel salts that form over time. Usually the buildup of these green-colored salts is slow, but if the overall chemistry of your plating bath is off, the buildup rate may be more rapid. For example, nickel hydroxide has a greenish color and can form if there is a small amount of hydroxide ions in the bath. Probably the simplest solution is to drain your plating tank, clean it and than place the plating solution back in the tank. You must perform one more step before using the bath, however. Carefully check out the chemistry of the bath, and pay particular attention to the pH as well as the amount of boric acid present. Changes in pH and low boric acid can increase the amount of hydroxide present and will lead to a greater rate of nickel hydroxide formation.