Nickel plating

Electroplating of nickel can be performed on different substrate materials, among which the most usual are steel and copper alloys. For the nickel plating of steels in earlier years a layer of copper was first applied. At the present time the nickel coating is plated directly on the steel surface. A thin outer layer (0.3 pm) of chromium is applied over the nickel to keep the luster. Nickel is electrochemically nobler than steel in ordinary corrosion environment, e.g. salt water. Thus nickel does not give any cathodic protection at defects that penetrate the layer. For corrosion protection of steel the nickel layers therefore need to be free from defects. 

Nickel plating of plastics, especially ABS and mixtures of ABS and polycarbonate, is also possible nowadays. Plating of nonconductive substrates starts with an electroless (autocatalytic) nickel plating. 

Nickel powder with very small grain size can adsorb up to 17 times of its own volume of hydrogen. This powder is used as a catalyst for many processes, e.g. hydrogenation of vegetable oils and cracking of ammonia to nitrogen and hydrogen. 

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Electroless plating on metal substrates can be improved by addition of pentaerythritol, either to a photosensitive composition of a noble metal salt (99), or with glycerine to nickel plating solutions (100). Both resolution and covering power of the electrolyte are improved. 

Many electroless coppers also have extended process Hves. Bailout, the process solution that is removed and periodically replaced by Hquid replenishment solution, must still be treated. Better waste treatment processes mean that removal of the copper from electroless copper complexes is easier. Methods have been developed to eliminate formaldehyde in wastewater, using hydrogen peroxide (qv) or other chemicals, or by electrochemical methods. Ion exchange (qv) and electro dialysis methods are available for bath life extension and waste minimi2ation of electroless nickel plating baths (see... 

G. G. Gawrilov, Chemical (Electroless) Nickel-Plating, PortcuUis Press, RedhiU, U.K., 1979. 

Nickel Fluoroborate. Fluoroboric acid and nickel carbonate form nickel fluoroborate [14708-14-6] Ni(BF 2 6H20. Upon crystallization, the high purity product is obtained (47). Nickel fluoroborate is used as the electrolyte ia specialty high speed nickel plating. It is available commercially as a concentrated solution. 

Electroplating. The second-largest appHcation for nickel chemicals is as electrolytes ia nickel electroplating (qv). In ordinary plating systems, nickel present ia the electrolyte never forms on the finished workpiece the latter results from dissolution and transfer from nickel anodes. Decorative nickel plating is used for automobile bumpers and trim, appHances, wire products, flatware, jewelry, and many other consumer items. A comprehensive review of nickel electroplating has been compiled (164). 

A principal commercial appHcation of the hypophosphites is ia the electroless plating (qv) process. Nickel salts are chemically reduced by hypophosphites to form a smooth adherent nickel plating to protect the iateriors of large vessels and tank cars. The coating, which can be hardened by heat treatment, usually contains 8—10 wt % phosphoms and is highly impervious. 

Approximately 4500 tons of sodium hypophosphite [7681-53-0] NaH2P02, was produced in 1990. This material is used principally in electroless nickel plating of plastic objects. Of the secondary products made from primary phosphoms compounds, phosphoms oxychloride is manufactured in the largest volume. Phosphoms pentachloride and phosphoms sulfochloride are made from phosphoms trichloride. 

Selenium and selenium compounds are also used in electroless nickel-plating baths, delayed-action blasting caps, lithium batteries, xeroradiography, cyanine- and noncyanine-type dyes, thin-film field effect transistors (FET), thin-film lasers, and fire-resistant functional fluids in aeronautics (see... 

To complete the assembly of a cell, the interleaved electrode groups are bolted to a cov er and the cover is sealed to a container. Originally, nickel-plated steel was the predominant material for cell containers but, more recently plastic containers have been used for a considerable proportion of pocket nickel-cadmium cells. Polyethylene, high impact polystyrene, and a copolymer of propylene and ethylene have been the most widely used plastics. 

To reduce labor and other expenses, most sintered nickel plaques are produced by a wet-slurry method. A nickel slurry is prepared by mixing a low density nickel powder with a viscous aqueous solution such as carboxymethylceUulose [9004-42-6] (CMC). Pure nickel gau2e, a nickel-plated gau2e, or a nickel-plated perforated steel strip is continuously carried through a container filled with the nickel paste and sintering is done in a hori2ontal furnace. The time of the sinter in the furnace is ca 10—20 min. 

CeU terminal connections are usuaUy brought out by two-threaded terminals that protmde through the ceU jar cover. They are usuaUy steel, brass, or copper with a hoUow coastmctioa. The plate leads are soldered ia place ia the ceater hoUow portioa of the terminal to effect an electrical contact and ceU seal. The terminal itself is potted iato the jar cover usiag epoxy-type pottiag compouads. NormaUy, terminal hardware is sUver-plated. However, for corrosioa resistance nickel-plating has been used. 

Electrodeposition of Metals. Citric acid and its salts are used as sequestrants to control deposition rates in both electroplating and electroless plating of metals (153—171). The addition of citric acid to an electroless nickel plating bath results in a smooth, hard, nonporous metal finish. 

R. Bmgger, Nickel Plating. A Comprehensive Review of Theory, Practice, Properties, and Applications Including Cobalt Plating, Draper, Teddington, UK, 1970. 

K. M. Gorbunova and A. A. Nikiforova, Phjsiochemical Principles of (Chemical) Nickel Plating Academy of Sciences, Moscow, 1960 (Engl, trans. available from U.S. Government Office of Technical Services, Washington, D.C., 1963). 

Since the 1960s titanium mesh anode baskets have been used (21), especially in nickel plating solutions. Nickel anodes in the form of small round buttons and pellets combined with the titanium anode basket allows a constant anode area to be maintained with a minimum of effort. 

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