Nickel coating is the oldest and most widely used decorative and protective coating. Since the British J. Shore obtained the first patent for nickel plating in 1840, the nickel plating process has been continuously developed, the plating species have been increasing, and its application has also developed from the traditional protective and decorative coating to a variety of functional coatings. The application of nickel plating layer is almost throughout all sectors of modern industry. In the electroplating industry, the output of nickel plating layer is second only to that of galvanized layer.
Nickel metal has high chemical stability, and has good corrosion resistance in dilute acid and dilute base organic acid. Nickel metal has good atmospheric corrosion resistance due to the interaction between nickel and oxygen in the air. However, due to the high porosity of the nickel plating layer, and the electrode potential of nickel is more correct than that of iron, so that the nickel coating can effectively prevent corrosion in air and some corrosive media only when it is thick enough and there is no gap.
Therefore, multi-layer Ni-Cr system and different Ni-coating combinations are often used to improve the protection performance. Nickel plating is mainly used in daily hardware products, automobiles, bicycles, motorcycles, household appliances, instruments, meters, cameras and other parts, as a protective - decorative coating of the intermediate coating. Due to the high hardness of nickel coating, it is used to improve the surface hardness in the printing industry, and is also used in electroforming and plastic molding molds. Nickel plating process can be divided into ordinary nickel plating (dark nickel), bright nickel plating, black nickel, hard nickel, multilayer nickel and so on according to the appearance and structural characteristics of the coating.
According to the composition of the bath, there are sulfate type, chloride type, citrate type, sulfamate type, fluoroborate type and so on. Among them, the most commonly used is sulfate low chloride nickel plating solution (that is, Watt plating solution). The internal stress of the sulfamate plating solution is small, the deposition speed is fast, but the cost is high, and it is only used in specific occasions. Citrate bath is often used for nickel plating on zinc die casting. Fluoroborate bath is suitable for thick nickel plating, but the cost of these types of bath is higher.
