Nickel coatings decorative

Decorative coatings It is impossible to give a comprehensive list of the uses of nickel coatings but applications of decorative nickel coatings, usually with a chromium top-coat, are given below ... 

Watts bath — The Watts bath is the classical electrolyte for the -> electrodeposition of functional nickel coatings. It contains nickel sulfate (240-450 gL-1 of the hexahy-drate), nickel chloride (45-90 gL-1 of the hexahydrate), and boric acid (30-50 g L-1) and is usually operated between pH 2 and 4.5 and at 40-70 °C. The chloride content of the bath is crucial to ensure the dissolution of the nickel anode. In combination with - leveling agents and brighteners the Watts bath is also used for decorative nickel coatings. Its applicability for -> electroforming is limited due to tensile stresses in the deposits. 

Although originally intended for evaluation of nickel-containing decorative electroplated coatings, the Corrod-kote test, ASTM B 380, has been used to qualify the performance of galvanized products for automotive applications. Apparently, the chloride ions introduced in this process provide a useful indication of automotive underbody performance for products such as tubing for containment of automotive fluids and other small components. The Corrodkote test applies a corrosive slurry to the... 

Nickel tarnishes rapidly in a corrosive environment. Nickel coatings are very useful as long as a decorative appearance is not required. However, if the nickel coatings are to maintain the decorative appearance, they are given a bright chromium overlay. Nickel offers a high degree of resistance to corrosion and oxidation in seawater. 

As mentioned earlier, a thin overlay of chromium is applied on nickel coating to prevent the corrosion of nickel coatings. Chromium is generally applied in the form of electrodeposit. As chromium coating is resistant to corrosion and has a bright luster, it is used as a decorating coating. Chromium is more active than iron (E° = -0.76 V) and has a tendency to become passive. 

A.STM B604, Std. Spec, for Decorative Electroplated Coatings of Copper) Nickel) Chromium on Plastics, American Society for Testing and Materials, Philadelphia, Pa., 1991. 

Wesley, W. A., Pitting of Decorative Nickel-Chromium Coatings , Tech. Proc. Am. Electroplaters Soc., 50, 9 (1963)... 

Decorative coatings of nickel plus chromium are cathodic to steel or zinc alloy substrates and with these protective systems deliberate use may be made of discontinuities in the chromium topcoat where corrosion of the underlying nickel will occur. If the number of these discontinuities in the chromium layer is greatly increased the current density at each individual corrosion site is reduced, penetration of corrosion through the thickness of the nickel layer is thus slowed down and the period of protection of the substrate metal is prolonged. 

The fact that the composition of the speculum deposit must be closely controlled to obtain the best results has been a serious drawback to development. The coating finds uses on decorative hollow-ware, oil lamps and tableware. The bronze deposits with 10 or 20% tin are used lacquered in decorative metal-ware for domestic and personal ornament and, in thick layers to protect hydraulic pit props against corrosion and abrasion. They have also been used with success as undercoatings for nickel-chromium or tin-nickel alloy deposits. 

Toys, office equipment, sports equipment and shop furniture also provide large markets for decorative coatings of nickel or nickel plus chromium. 

Wearmouth has described the production of nickel-cobalt, nickel-manganese, and nickel-chromium alloy coatings for non-decorative uses. The nickel-cobalt and nickel-manganese are electrodeposited direct from sulphamate-based solutions, the nickel-cobalt alloys offering higher hardness than the nickel-manganese alloys, which are restricted to a relatively... 

Chromium makes up just 0.012% of the Earth s crust, yet it is an important industrial metal. The main use of chromium is in metal alloys. Stainless steel, for example, contains as much as 20% chromium. Nichrome, a 60 40 alloy of nickel and chromium, is used to make heat-radiating wires in electrical devices such as toasters and hair dryers. Another important application of chromium metal is as a protective and decorative coating for the surface of metal objects, as described in Chapter 19. 

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