Q. Our sulfamate nickel plating bath is giving us problems. Most recent tests show the chloride content to be 10.15 g/L, and our control limits are 3-9 g/L. What can I do to reduce the chloride content? What will happen if the chloride content is too high? What caused the chloride content to increase? —S.P.
A. The use of chloride ions in sulfamate nickel baths has been debated for many years. Sulfamate baths are sometimes formulated with small amounts of nickel chloride to aid in anode efficiency. The downside of adding chloride ions is that, as the chloride concentration increases, the tensile strength of the nickel deposit will also increase. This increases the stress in the deposit, which, in turn, can cause cracking, etc.
The concentration that you report (10.15 g/L) is on the high side and should be reduced. The simplest way to reduce your chloride concentration is to dilute the bath and then bring other components up to the required concentration.
The elevated chloride concentration can be caused by a number of things: 1) an incorrect addition of nickel chloride, 2) using make-up water containing chloride ion, 3) using hydrochloric acid to control pH or 4) drag-in and drag-out issues.