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copper plating[′käp·ər ‚plād·iŋ]
the application of copper coatings to cleaned and pickled steel or zinc finished products, and some-times to steel wire, by electrodeposition. Copper plating is often used to protect individual sections of steel products against cementation (carbonization); in this case only the sections that are to undergo subsequent cutting are plated (because hard carbonized surface layers are not amenable to this type of mechanical working, and the copper protects the coated sections against diffusion of carbon within them). Copper plating is more widely used in the protective and decorative chrome plating of steel or zinc products, in which copper is the intermediate layer: a layer of nickel is applied to the copper, followed by a very thin layer of chromium (0.25 micron [μm]).
There are two types of copper electrolytes, acidic and alkaline. In the case of acidic electrolytes, it is impossible to obtain securely bonded copper coatings on steel and zinc products, since iron and zinc dissolve upon contact with copper, thereby disrupting the bond with the coating. Therefore, a thin layer of copper (2-3 μ) must be applied in an alkaline electrolyte, after which the coating is built up to the desired thickness in a more economical acidic electrolyte. Zinc items of complex shape are copper plated only in alkaline (cyanide) electrolytes.
V. I. LAINER