Electroless Black Nickel-Phosphorus (Ni-P) plating is an advanced electroless nickel plating process formulated to deposit a black finish when processed through an oxidizing acid solution.
Electrolesss nickel alloys are commonly used because of their beneficial physical and mechanical properties. Black electroless nickel coatings, commonly used in optical instruments and absorbing material, decorative coatings and aerospace industries, are specified due to their stability against sunlight exposure and their electrical conductivity and wear resistance.
By the oxidization of a low nickel-phosphorus alloy, the black electroless nickel plating is formed. When compared to medium or high phosphorus alloys, this black alloy has an improved wear resistance and a deeper black finish. This is desired for both the looks and the benefits of a tougher and more rugged finish.
During the experimentation process performed in order to create this new type of electroless nickel plating, some very interesting facts and findings were discovered and analyzed until the perfect balance of immersion time and temperature of the solution was reached to create black electroless nickel plating. The black color of the nickel-phosphorus coating arises from its unique surface morphology combined with the formation of nickel oxides and nickel phosphate.
The phosphorus, sulfur, oxygen and nickel contents of Ni-P coatings with various etching times were tested. The results showed that the nickel content decreased with an increase in immersion time, suggesting that only nickel atoms in the nodular surface were preferentially removed while other nickel atoms formed oxides, (such as NiO and Ni2O3) causing the phosphorous and oxygen contents to increase at the black Ni-P surface.
The variation in intensity of the black finish was also tested with various immersion times. At 30 seconds and one minute immersion times, iridescence is noted on the black Ni-P coating. The iridescence phenomenon is caused by the nodules not being completely etched away. When the black Ni-P was immersed for longer times of two and five minutes, the black Ni-P coatings were iridescence-free with intense black color. Another benefit besides the black color is the smoother surface and larger nodular structures.
Black electroless nickel plating is a very attractive alternative to the conventional Electroless Nickel Plating. The end result is a finish that is darker than black chrome and more opaque than black anodize with a unique metallic finish. At AST, we are proud to offer this special type of Black Electroless Nickel Plating along with a large number of specialty Electroless Nickel plating systems. All parts treated by any of AST’s plating systems have superior resistance to corrosion and rust. With over four decades of experience in the metal finishing industry, contact us today to find the perfect solution to job.