Electroless nickel-phosphorus plating
[4] In 1911, François Auguste Roux of L'Aluminium Français patented the process (using both hypophosphite and orthophosphite) for general metal plating.
When they added sodium hypophosphite, they observed that the amount of nickel that was deposited at the cathode exceeded the theoretical limit of Faraday's law.
[6][7] Brenner and Riddel presented their discovery at the 1946 Convention of the American Electroplaters' Society (AES);[8] a year later, at the same conference they proposed the term "electroless" for the process and described optimized bath formulations,[9] that resulted in a patent.
[citation needed] During 1954–1959, a team led by Gregorie Gutzeit at General American Transportation Corporation greatly developed the process, determining the optimum parameters and concentrations of the bath, and introducing many important additives to speed up the deposition rate and prevent unwanted reactions, such as spontaneous deposition.
[citation needed] If the substrate is not conductive, such as ABS and other plastics, one can use an activating bath containing a noble metal salt, like palladium chloride or silver nitrate, and a suitable reducing agent.
[citation needed] Activation is done with a weak acid etch, nickel strike, or a proprietary solution, if the substrate is non-metallic.
After plating, an anti-oxidation or anti-tarnish chemical coating, such as phosphate or chromate, is applied, followed by rinsing with water and dried to prevent staining.
Baking may be necessary to improve the hardness and adhesion of the plating, anneal any internal stresses, and expel trapped hydrogen that may make it brittle.
In that study, in an intermediate layer, finely powdered particles, like aluminum oxide and polyvinyl chloride (PVC) resin, were distributed within a metallic matrix.
The feasibility to incorporate the second phase of fine particles, the size of a nanometer to micrometer, within a metal-alloy matrix has initiated a new generation of composite coatings.
[3] Compared to the electrolytic process, a major advantage of electroless nickel plating is that it creates an even coating of a desired thickness and volume, even in parts with complex shape, recesses, and blind holes.
[16] If properly formulated, EN plating may also provide a less porous coating, harder and more resistant to corrosion and hydrogen absorption.
The specific characteristics vary depending on the type of EN plating and nickel alloy used, which are chosen to suit the application.
[citation needed] Electroless nickel-phosphorus coatings with less than 7% phosphorus are solid solutions with a microcrystalline structure, with each grain 2–6 nm across.
Its uniform deposition profile means it can be applied to complex components not readily suited to other hard-wearing coatings like hard chromium.
However, it is important to recognize that only End of Life Vehicles Directive or RoHS compliant process types (free from heavy metal stabilizers) may be used for these applications.
