Electroless nickel-boron coatings

Electroless nickel-phosphorus should not be used with either fused or hot, strong, aqueous caustic solutions because the coating offers lower resistance to attack than does electrodeposited nickel. As-deposited electroless nickel-boron, however, offers good resistance to hot aqueous caustic solutions It is also resistant to solutions of oxidising salts such as potassium dichromate, permanganate, chlorate and nitrate. 

Another important function of metallic coatings is to provide wear resistance. Hard chromium, electroless nickel, composites of nickel and diamond, or diffusion or vapor-phase deposits of sUicon carbide [409-21-2], SiC , SiC tungsten carbide [56780-56-4], WC and boron carbide [12069-32-8], B4C, are examples. Chemical resistance at high temperatures is provided by aUoys of aluminum and platinum [7440-06-4] or other precious metals (10—14). 

Electroless Electrolytic Plating. In electroless or autocatalytic plating, no external voltage/current source is required (21). The voltage/current is suppHed by the chemical reduction of an agent at the deposit surface. The reduction reaction must be catalyzed, and often boron or phosphoms is used as the catalyst. Materials that are commonly deposited by electroless plating (qv) are Ni, Cu, Au, Pd, Pt, Ag, Co, and Ni—Fe (permalloy). In order to initiate the electroless deposition process, a catalyst must be present on the surface. A common catalyst for electroless nickel is tin. Often an accelerator is needed to remove the protective coat on the catalysis and start the reaction. 

Electroless Ni coatings are produced by autocatalyt-ical reduction of Ni ions from aqueous solution. Three electroless coatings are applied most frequently nickel-phosphorus (6-12wt%P), nickel-boron ( 5wt%B), and composite coatings (Ni—P with SiC, fluorocarbons, and diamond). A more extensive account is given in [1.96]. 

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. 

Fluorinated surfactants improve the quality of electroless plating of copper [67,68] and stabilize the coating bath to deposit nickel-boron layers without a dentritic layer structure [69]. 

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