Nickel Plating

the application to the surface of articles of a nickel coating 1–2 to 40–50 microns (μ) thick. Nickel plating is used mainly on articles made from steel and alloys based on copper, zinc, aluminum, and less frequently magnesium, titanium, tungsten, molybdenum, and their alloys. Methods have been developed for the application of nickel to nonmetallic surfaces, such as ceramics, plastics, Bakelite, porcelain, and glass. Nickel plating is used to protect articles from corrosion (under atmospheric conditions and in solutions of alkalies, salts, and weak organic acids) and to increase the wear resistance of parts, as well as for protective and decorative purposes.

The most widespread methods of nickel plating are the electrolytic and chemical methods. Nickel plating is most frequently performed by the dull electrolytic method. Sulfuric-acid electrolytes are the most thoroughly studied and stable nickel-plating media. Bright nickel plating is achieved by the addition of luster-forming agents to the electrolyte. The electrolytic coatings have some porosity, which depends on the degree of care exercised in the preparation of the substrate surface and on the thickness of the coating. Corrosion protection requires a complete absence of pores; therefore, copper plating is performed first or multilayer coatings are applied, which are more reliable than single-layer coatings of equal thickness (steel parts are frequently coated sequentially with copper, nickel, and chromium).

The disadvantages of electrolytic nickel coatings are nonuniform deposition of nickel on relief surfaces and the impossibility of plating narrow and deep openings, cavities, and so on. Chemical nickel plating is somewhat more expensive than electrolytic plating, but it makes possible the deposition of coatings of uniform thickness and quality on any areas of relief surfaces that are accessiblle to the solution. The process is based on reduction of nickel ions from its salts using sodium hypophosphite or another reducing agent in aqueous solutions.

Nickel plating is used to coat parts of chemical equipment, automobiles, bicycles, medical instruments, household articles, measuring instruments, engraving plates, and stereotypes, as well as parts that are used under moderate loads under conditions of dry friction. Nickel coatings lose some of their initial luster over time. Therefore, the nickel layer is covered with a more stable chromium layer.