The history of electroless nickel plating solutions is relatively brief compared to electroplating. Its true industrial application abroad only began in the late 1970s to early 1980s. In 1844, A. Wurtz discovered that metallic nickel could be reduced and deposited from aqueous nickel salt solutions using hypophosphite. The true discovery of electroless nickel plating technology, which remains in use today, was made in 1944 by A. Brenner and G. Riddell at the U.S. National Bureau of Standards. Their work clarified the catalytic nature of coating formation and developed a method for depositing non-powdery nickel, making industrial application of electroless nickel plating possible.
However, the electroless nickel plating solutions at that time were extremely unstable and therefore had no practical value in the strict sense. The industrial application of electroless nickel plating lagged behind laboratory research results by nearly a decade. After World War II, the American General Transport Company became interested in this process, as they wanted to plate the inner surfaces of caustic soda shipping drums—something impossible with conventional electroplating methods. Five years later, they researched and developed electroless nickel-phosphorus alloy technology, publishing numerous patents. In 1955, they built their first experimental production line and created a commercially viable electroless nickel plating solution under the trade name "Kanigen."
Abroad, particularly in the United States, Japan, and Germany, electroless nickel plating has become a highly mature advanced technology, finding widespread application across various industrial sectors. China's industrial production of electroless nickel plating started relatively late, but has developed rapidly in recent years. Not only has a large volume of research papers been published, but national electroless plating conferences have also been held. According to statistics from the 5th Electroless Plating Annual Conference, there were already over 300 manufacturers, though this figure was likely extremely conservative at the time. It is estimated that China's annual electroless nickel plating market totals approximately 30 billion RMB, growing at a rate of 10%–15% per year.
The specific process refers to: under certain conditions, metal ions in aqueous solution are reduced by a reducing agent and precipitate onto the surface of a solid substrate. ASTM B374 (ASTM: American Society for Testing and Materials) defines autocatalytic plating as "deposition of a metallic coating by a controlled chemical reduction that is catalyzed by the metal or alloy being deposited." This process differs from displacement plating, as the coating can continuously thicken, and the deposited metal itself possesses catalytic activity.
(I) Characteristics, Properties, and Applications of Electroplated Nickel:
1. Electroplated nickel coatings exhibit high stability in air. Due to nickel's strong passivation ability, an extremely thin passive film rapidly forms on the surface, providing resistance to atmospheric, alkaline, and certain acidic corrosion.
2. Electroplated nickel has an extremely fine crystalline structure and excellent polishing properties. Polished nickel coatings can achieve a mirror-like lustrous appearance that is maintained for extended periods in atmospheric conditions. Therefore, nickel coatings are commonly used for decorative purposes.
3. Nickel coatings have relatively high hardness, which can improve surface wear resistance. In the printing industry, nickel plating is frequently used to increase the hardness of lead surfaces. Due to nickel's high chemical stability, thicker nickel coatings are also used in chemical equipment to prevent corrosion by various media.
Nickel coatings are also widely applied for functional purposes, such as refurbishing worn or corroded parts using brush plating techniques for localized electroplating. Electroforming processes are employed to produce printing plates, record molds, and other tooling. Thick nickel coatings provide good wear resistance and serve as wear-resistant platings. Particularly in recent years, the development of composite electroplating has enabled the deposition of nickel coatings containing wear-resistant particles, offering even greater hardness and wear resistance than conventional nickel platings. When graphite or fluorinated graphite is used as dispersed particles, the resulting nickel-graphite or nickel-fluorinated graphite composite coatings exhibit excellent self-lubricating properties, making them suitable for lubrication applications. Black nickel coatings also find extensive use as optical instrument coatings or decorative finishes.
4. Nickel plating has broad applications as a protective decorative coating on steel, zinc die castings, aluminum alloys, and copper alloys, protecting substrates from corrosion or providing bright decorative finishes. It is also commonly used as an intermediate coating, over which a thin chromium layer or an imitation gold layer is deposited for enhanced corrosion resistance and aesthetic appeal. For functional applications, nickel plating 1–3 mm thick on specialized industry components can achieve restoration purposes. Applications are increasingly widespread, particularly in continuous casting molds, electronic component surface dies, alloy die-casting molds, complex aerospace engine components, and microelectronic device manufacturing.
5. In electroplating processes, due to its superior properties, nickel plating ranks second only to zinc plating in processing volume, accounting for approximately 10% of total nickel production.
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Author: Bo Wang, Engineering Department.