Metallic coatings electroless nickel plating

Electroless nickel plating is used to deposit a coating of nickel or nickel alloy on a substrate. It relies on the presence of a reducing agent that reacts with the metal ions to deposit metal. This process uses a unique chemical bath without any electrical current. The bath chemistry is constantly replenished during the plating process. 

Coatings are also produced by electroless plating—that is, by chemical reduction of metal-salt solutions, with the precipitated metal forming an adherent overlay on the base metal. Nickel coatings of this kind are called electroless nickel plate. 

The Niphos process (1955) represents an alternative method of electroless nickel plating [45], A paste of composition NiO = 70%, (NH4)2HP04 = 15%, H2O = 15% is coated on to a clean metal surface which is then processed in a hydrogen atmosphere at 900°C. It is claimed that reduction to the metal occurs and a coating of nickel is obtained, similar to that from the hypophosphite process above. 

Surfaces can also be coated without involving electricity. Electroless nickel plating, for example, involves pretreating the surface of any material, including nonconductive materials, with a catalyst such as sodium hypophosphite. This treated surface is then immersed in a heated nickel-phosphorous or nickel-boron solution. The metal ions from the solution are reduced to metal in contact with the catalyst and form a dense alloy layer on the treated surface. 

Modem electroless plating began in 1944 with the rediscovery that hypophosphite could bring about nickel deposition (7,8). Subsequent work led to the first patents on commercially usable electroless nickel solutions. Although these solutions were very useful for coating metals, they could not be used on most plastics because the operating temperature was 90—100°C. The first electroless nickel solution capable of wide use on plastics was introduced in 1966 (9). This solution was usable at room temperature and was extremely stable (see Nickel and nickel alloys). 

Some firearms are plated with anodized aluminum, nickel, or chromium which gives durability and good looks, and some are made from stainless steel which is much less prone to rust than conventional steel. Electroless nickel coating is an alloy coating of 88% to 96% nickel and 4% to 12% phosphorus, which is produced by chemical (not electrical) reduction of nickel on to the metal surface. 

Electroless plating — An autocatalytic process of metal deposition on a substrate by reduction of metal ions from solution without using an external source of electrons. It is promoted by specific reductants, namely formaldehyde, sodium hypophosphide, sodium boro-hydride, dialkylamine borane, and hydrazine. Electroless deposition has been used to produce different metal (e.g., nickel, cobalt, copper, gold, platinum, palladium, silver) and alloy coatings. It can be applied to any type of substrate including non-conductors. Some substrates are intrinsic catalytic for the electroless deposition other can be catalyzed usually by sensibilization followed by Pd nucleation also, in some non-catalytic metallic substrates the electroless process can be induced by an initial application of an appropriate potential pulse. In practical terms, the evaluation of the catalytic activity of a substrate for the electroless deposition of a given metal is... 

In electrochemical composite plating inert particles are deliberately added to the plating bath to obtain metal matrix composite coatings. Figure 1 shows an example of metal matrix composite coating of electroless nickel-phosphorous in which silicon carbide particles are incorporated. The particle materials used should be inert to the bath in the... 

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