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:

Nickel salts

Nickel chloride

Formula is NiCl2 ■ 6H2O. Contains 24.7% Ni.

Nickel sulfate

Formula is NiSO4 ■ 6H2O. Contains 22.3% Ni.

Nickel sulfamate

Formula is Ni(NH2SO3)2. Contains 23.2% Ni.

Nickel carbonate

Formula is NiCO3. Contains about 46% Ni.

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.

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