Nickel Plating
THE NICKEL PLATING PROCESS is used extensively for decorative, engineering, and electroforming purposes
because the appearance and other properties of electrodeposited nickel can be varied over wide ranges by controlling the
composition and the operating parameters of the plating solution. Decorative applications account for about 80% of the
nickel consumed in plating; 20% is consumed for engineering and electroforming purposes. Autocatalytic (electroless)
nickel plating processes are commercially important but are outside the scope of this section. The annual worldwide
consumption of nickel for electroplating is approximately 180 million pounds (81,700 metric tons) and accounts for 11 to
12% of world nickel consumption. Some basic information about nickel and common nickel salts for plating is given in
the following table:Decorative Plating. Modern decorative nickel plating solutions contain organic additives that modify the
electrocrystallization process so that mirror-bright, highly-leveled nickel coatings are deposited directly from solution.
Prior to the introduction of "organic" baths, decorative nickel coatings were produced by polishing nickel-plated parts
mechanically, a practice that continued from 1870 to about 1945. Thin layers of chromium were electrodeposited over
polished nickel coatings for the first time in 1927 to prevent the "yellowing" or tarnishing of nickel in outdoor
atmospheres, and that practice continues with the "as-deposited" bright nickel coatings now available. An effort to
develop improved decorative, electroplated nickel coatings began in the late 1940s and led to the development of
multilayer nickel coatings (early 1950s) and microdiscontinuous chromium coatings (mid- to late 1960s). Modern
multilayer nickel coatings in combination with microdiscontinuous chromium are capable of protecting and enhancing the
appearance of most metals and alloys, plateable plastics, and other materials for extended periods of time.
Engineering Plating. The engineering applications of nickel plating include those where a fully bright appearance is
not required. Engineering nickel deposits are usually sulfur-free and matte in appearance. These deposits may be specified
to improve corrosion and wear resistance, to salvage or build up worn or undersized parts, to modify magnetic properties,
to prepare surfaces for enameling or for organic coating, to function as diffusion barriers in electronic applications and for
other purposes. Engineering applications exist in the chemical, nuclear, telecommunications, consumer electronics, and
computer industries.
Electroforming. Nickel electroforming is electrodeposition applied to the manufacture of nickel products of various
kinds, and it differs from electroplating in one major respect. In electroplating, the coating is metallurgically bonded to
the substrate and is an integral part of the surface. In electroforming, nickel is deposited onto a mandrel or mold
nonadherently so that the nickel can be separated from the mandrel when it is removed from the plating solution.
Electroforming applications include the fabrication of molds and dies, mesh, and other products that are indispensable to
operations in the textile, aerospace, communication, electronics, automotive, photocopying, and entertainment industries.
Additional information is available in the article "Electroforming" in this Volume.
Basic Process Considerations
Before describing decorative, engineering, and electroforming plating processes, some basic facts are reviewed that make
it possible to control the nickel plating process, predict the amount of nickel deposited, and estimate nickel coating
thickness.
The Basic Process. Nickel plating is similar to other electroplating processes that employ soluble metal anodes. It
requires the passage of direct current between two electrodes that are immersed in a conductive, aqueous solution of
nickel salts. The flow of direct current causes one of the electrodes (the anode) to dissolve and the other electrode (the
cathode) to become covered with nickel. The nickel in solution is present in the form of divalent positively charged ions
(Ni++). When current flows, the positive ions react with two electrons (2e-) and are converted to metallic nickel (Ni0) at
the cathode surface. The reverse occurs at the anode, where metallic nickel is dissolved to form divalent positively
charged ions, which enter the solution. The nickel ions discharged at the cathode are replenished by those formed at the
anode.

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