Sulfur embrittlement of Ni sulfamate platings

A. I very strongly doubt that sulfur depolarized anodes are the cause of the sulfur embrittlement. And while I am not a smart enough chemist to truly understand azodisulfonate and the "magic stress reducers" associated with nickel sulfamate plating, I doubt that they are the cause either. My understanding, inferred from people who are the smart enough chemists, is that these sulfur deposition problems invariably come from brighteners and leveling agents that someone deliberately put into the bath, or from oils of some sort that found their way in.

A. I have never heard of sulfur depolarised nickel causing sulfur induced hardening or embrittlement. However, many additives, such as saccharin, have sulfur in their molecular structure and when they are co-deposited , they can cause sulfur embrittlement. This is only usually seen when the nickel is heated to over 160 °C - the higher the temperature the shorter the time needed to see it. At 160 °C it takes about 2 hrs.

A. Sulfur depolarized anodes are definitely not a source for sulfur in the nickel deposition. During running a sulfamate electrolyte there is the possibility to create azodisulfonate, which is a source for sulfur in the deposition. The azodisulfonate is created at polarized anodes (Reasons for high polarization can be: To low chloride content, to high anodic current density, wrong anode material). Sulfur depolarized anodes help to prevent the creation of azodisulfonate even in low-chloride sulfamate bath.