Black Nickel

What is black nickel, and is it a good process for adding corrosion protection to parts?


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Q: What is black nickel, and is it a good process for adding corrosion protection to parts? M. J. K.

 

A: Black nickel must be the hot process this year, because I have received a number of questions regarding the finish. In my experience, black nickel has always had some “black magic” (pun intended) involved in the process. To start with, black nickel is an alloy of nickel, zinc and nickel sulfide. Alloy plating baths generally are very sensitive to operating conditions. In this case, changing current density will change the appearance and properties of the deposit. A high current density will give you a shiny bright gray finish. To obtain a dull finish, a low current density must be used. Other factors that will affect the black nickel deposit are solution composition, pH, and temperature. Quite often, the surface is etched prior to applying the black nickel plate.

Black nickel is usually applied in very thin layers because it is a rather brutal deposit. Generally, it does not give very good corrosion resistance; to improve protection when using black nickel, a dull nickel layer is applied before the black nickel. If a brighter finish is required, a bright nickel is applied instead of the dull nickel layer. The black nickel deposit usually appears dark gray when applied and black when coated with a suitable organic coating.

A typical black nickel formulation is as follows. Other formulations can be found in the literature. 

Chemical ComponentConcentration (g/L)
Double nickel salts [Ni(NH4)2(SO4)3.6 H2O]60
Zinc sulfate (ZnSO4.6 H2O)7.5
Sodium thiocyanate (NaCNS)15
Operating ConditionsRange
pH5.5–6.0
Temperature24°C
Nickel metal concentration9 g/L
 

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