Abstract:
Since its introduction in 1946, applications of the electroless (EL) deposition process have seen steady growth. Electroless nickel, cobalt and copper coatings have found considerable usage in the general engineering, electronics, semi-conductor, aerospace and plastics industries; particular interest has centered on the potential of nickel coatings, which offer superior protection, by virtue of their improved resistance to atmospheric corrosion and wear relative to conventional electrolytic nickel coatings. Further advantages. lie in the thinner, denser nature of electroless coatings, and the exceptionally good throwing power of the process, making possible the successful coating of small, light and intricate components.
Electroless (EL) co-deposition of inert particles, represents a method to obtain metal matrix composite materials as thin foils (coatings) at low temperature (90°C). Compared to electrodeposition, electroless can be applied on different substrates (conductive and nonconductive) and the obtained layer has a very homogeneous distribution regardless the substrate, geometry. An electroless nickel composite coating consists of small inert particles, such as: oxides, carbides, nitrides polymers etc., uniformly dispersed into a nickel-based matrix. During the redox reaction between Ni ions and sodium hypophosphite, the inert particles are physically entrapped in a growing Ni-P layer on the substrate surface. Each combination between a certain type of particle and the Ni-P matrix can led to a new set of properties. Generally, in electroless nickel particles co-deposition, particle concentration in the deposit deposition on factors like: bath chemistry (mainly type and amount of surfactant), particle characteristics ( e.g. density, size distribution) and operating conditions (e.g. bath stirring, substrate position and movement).
