Coatings nickel

Nickel coatings are usually prepared by electroplating. The metal is plated either directly on steel or sometimes over an intermediate coating of copper. The copper underlayer is used to facilitate buffing of the surface on which nickel is plated, because copper is softer than steel, and also to reduce the required thickness of nickel (which costs more than copper) for obtaining a coating of minimum porosity. The automotive industry uses nickel as an underlayer for microcracked chromium to protect steel [9]. 

Electroless nickel plate is produced primarily for the chemical industry. Nickel salts are reduced to the metal by sodium hypophosphite solutions at or near the boiling point. A typical solution is the following  

This particular formulation deposits nickel at the rate of about 0.015 mm (0.6mil)/h in the form of a nickel-phosphorus alloy [13]. The usual range of phosphorus content in coatings of this kind is 7-9%. Various metal surfaces, including nickel, act as catalysts for the reaction so that deposits can be built up 

Relatively flat parts of the surface can be observed both for the nickel coating obtained in the presence of the basic brightening addition agent only and the nickel coating obtained in the presence of both the basic and top brightening addition agents (Fig. 35). From Fig. 

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Nickel-coated powder products are used as conductive pigments for appHcation in surface coatings (qv), adhesives (qv), injection mol ding powders. 

Nickel-Coated Graphite-60, Product Data Sheet, Novamet Specialty Products Corp., Wyckoff, N.J., 1988. 

J. A. E. BeU and G. Hansen, "Properties of Nickel-Coated Carbon and Kevlar Fibers Produced by the Decomposition of Nickel Carbonyl," the 23rddntemational SAMPE Technical Conference, Anaheim, Calif, Society for the Advancement of Material and Process Engineering, Covina, Calif., Oct. 1991. 

Magnetic Method for Nickel Coatings on Magnetic and Non-magnetic Substrates... 

K. Parker, Internal Stress Measurements of Electroless Nickel Coatings by the Rigid Strip Method, ASTM STP 947, American Society for Testing and Materials, Philadelphia, Pa., 1987. 

Kutznelnigg, Pitting, the Typical Corrosion of Nickel Coatings , Korrosion, 13, 64 (1960) Schmeken, H., Electrochemical Measurements on Corrosion of Zinc with Regard to Pitting Possibilities , Korrosion, 13, 65 (I960)... 

The application of the tin-nickel coating for out of doors service has been restricted by fear of pore corrosion and of physical damage, and by... 

The case is different again under micro-discontinuous (i.e. micro-cracked or micro-porous) chromium, on which a definite improvement in corrosion resistance can be achieved when copper is present under the nickel coating . 

In double-layer nickel coatings however, a flat-based pit is formed in the nickel coating, giving marked resistance to penetration to the basis metal. Figure 13.8 shows a pit in a double-layer nickel plus chromium coating after 58 months service. 

Other aspects of engineering electrodeposited coatings A great deal of information has been published on important, but specialised, aspects of engineering nickel coatings. 

A major advantage of the electroless nickel process is that deposition takes place at an almost uniform rate over surfaces of complex shape. Thus, electroless nickel can readily be applied to internal plating of tubes, valves, containers and other parts having deeply undercut surfaces where nickel coating by electrodeposition would be very difficult and costly. The resistance to corrosion of the coatings and their special mechanical properties also offer advantages in many instances where electrodeposited nickel could be applied without difficulty. 

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