Bright nickel

Decorative plating primarily over bright nickel is estimated to consume about 2270 t worldwide. Some 60% of this is used in North America, and about 900 t in Europe. A relatively new method in decorative chromium plating is based on trivalent instead of hexavalent chromium, and this is estimated to total about 10% of the decorative market and is expected to increase. Chromic acid, which cost about 2.76/kg in early 1993, is the hexavalent... 

Bright Nickel. Nickel as electroplated from pure nickel salts is a dull grey, satin—like deposit that has to be buffed to obtain a bright finish. 

Triple Nickel and More. As an extension to the dual nickel, a thin, higher sulfur-containing nickel strike is deposited between the sulfur-free and the bright nickel. The sulfur content of this minimumally 2.5 p.m-sttike is 0.15—0.20 mass %. Ttiple nickel and dual nickel are covered by ASTM specification B456 (89). A fourth nickel deposit has shown improved protection by the effects it has on subsequent chromium deposits. Highly stressed, these nickel strikes have been used to aid in producing microcracked chromium. 

The Watts Solution, is a relatively cheap, simple solution which is easy to control and keep pure. The nigkel sulphate acts as the main source of nickel ions, though nickel chloride is an additional source. Higher deposition rates can be, used when the ratio of nickel chloride to nickel sulphate is raised and some proprietary bright nickel solutions are available in a high-speed version which contains an increased concentration of nickel chloride. 

Fig. 13.9 Triple-layer nickel deposit consisting of semi-bright and bright nickel layers with a thin, highly activated layer of nickel between them (after Reference 23)...

A crack count of 30-80 cracks/mm is desirable to maintain good corrosion resistance. Crack counts of less than 30 cracks/mm should be avoided, since they can penetrate into the nickel layer as a result of mechanical stress, whilst large cracks may also have a notch effect. Measurements made on chromium deposits from baths which produce microcracked coatings indicate that the stress decreases with time from the appearance of the first cracks . It is more difficult to produce the required microcracked pattern on matt or semi-bright nickel than on fully bright deposits. The crack network does not form very well in low-current-density areas, so that the auxiliary anodes may be necessary. 

In practice a special nickel solution containing the suspended particles is applied over the normal bright nickel deposit. The plating time in this solution is from 20 s to 5 min the most suitable ratio of the two deposits has to be determined in each particular case. 

Fogging reduction of the lustre of a metal by a film or particulate layer of corrosion product, e.g. the dulling of bright nickel surfaces. 

Bronze, copper—tin alloy, electro deposits can be produced in thicker deposits using proprietary brightening additives in the plating solution, especially over a smooth bright substrate. The brightest deposit with better corrosion resistance is attained when bronze is plated over a bright nickel plate. However, direct plating over steel is not an uncommon practice. 

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