Abstract
Abstract : Electroless nickel (EN) plating is used to apply a protective coating to a substrate without the use of an electric current. Following a catalytic activation step, a nickel phosphorous alloy (NiP) is deposited through chemical reactions on the surface of the part. The advantages over other metal coatings include: (1) coating uniformity, (2) corrosion resistance, (3) wear resistance, (4) desirable magnetic and electrical properties, and (5) indifference to part shape. The most common nickel source is nickel sulfate. Nickel ions are reduced to nickel metal by accepting electrons from an electron donor, typically hypophosphite, present in solution as sodium hypophosphite. Some of the hypophosphite is reduced to phosphorous, and is co-deposited with nickel to form a NiP alloy. As the nickel is plated onto the part, the concentrations of nickel and hypophosphite in the bath decrease. Nickel sulfate and sodium hypophosphite are periodically added to replenish these losses. When 100 percent of the original nickel has been replaced, this is termed a metal turnover (MTO).
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