August 5, 2008

Nickel Coating

Nickel plating is by far the most important electroplating process, chiefly because it is the best undercoating immediately below chromium plating. Nickel is a hard, yellowish-white, non-toxic metal with takes a high polish and has considerable resistance to tarnish and corrosion by weather. After prolonged exposure to damp industrial atmospheres it loses its polish and form a superficial haze or bloom, but the metal is not deeply corroded and the original luster can readily thick coating of nickel protects iron and steel from rusting, but only by excluding the corrosive environment from contact with the exposed spots is accelerated by its presence on adjacent areas.

Soon after the metal become commercially available, about 1870, nickel plating became popular for the protection and establishment of harness part and then fashionable bicycle. Subsequently it was used for all kinds of metal articles. Its use was stimulated by the advent of the motor car, particularly after 1930, when chromium plating became the major decorative, as well as the protective medium on motor cars and many other manufactured products. Out of total consumption in the UK in 1963 of 36,000 tons of nickel it is estimated that about 5,000 tons were used in electroplating, i.e. approximately one-seventh of the total consumed.

The most useful type of electroplating solution for nickel is the Watts solution. A typical composition is: see on nickel plating.

These condition correspond to a rate of deposition of 0.0008 to 0.0053 in/h. The voltage necessary varies with the current density, the temperature and the size of the vat, but is in the range of 3 to 7 V.

In the above formula, the nickel salts are quoted in the form of the hydrated crystalline material commercially available; in solution. Of course, this water of crystallization is no longer attached to the salts. The use of two different nickel salts is necessary to ensure the presence of some chloride ions, because with sulfate anions alone the nickel anodes do not dissolve freely, and the solution would become impoverished in nickel during use. The solution is almost saturated with nickel salts, to have the maximum amount of nickel ion available and to achieve a high current density.

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