Wednesday, April 16, 2008

High Sulfate Bath and Black Nickel Bath

High Sulfate solution is of the type developed by Thomson for plating nickel directly upon zinc alloys. The high content of sodium sulfate suppresses ionization of the nickel sulfate and thus ends to prevent the deposition of granular nickel by chemical displacement on the zinc surface. Live entry (hot contact) is usually used. Brighteners other than small concentrations of cadmium ions are not suitable in this bath because of the high concentration of ammonium ions and in general thickness less than about 15 μm are used with this cold bath. The covering and throwing powers through superior to a Watt bath are not compatible to the cyanide copper bath, and the later is practically universally used as the first plate on top of zinc die castings. This solution is useful when copper is not desired for desired for plating on aluminum and magnesium alloys which have been coated with zinc by an immersion process.

Black Nickel Bath
Black Nickel solution for deposition of a decorative black finish which contains not only nickel but also large amount of zinc and sulfur. A modification of this bath, which contain chlorides in place of sulfate, is said to be easier to control. Black nickel is a thin decorative finish which reproduces the underlying surface, lustrous black on smooth surface, and dull black on mat surface. It is used to achieved color effect and should not be considered corrosion resistant. A nickel undercoat is used protect the basis metal.

Alkaline Nickel Bath
Nickel can be deposited from alkaline baths, and baths of this type have been developed mainly for direct plating of zinc die castings with the view of eliminating the need for cyanide copper as the first plate and also for obtaining generally better throwing power. These baths in general give rather brittle plate. The bond to zinc is good but not always the best. It is mainly for this reasons that these bath are seldom used. However, an early bath consisting of ammoniac pyrophosphate and citrate complexes of nickel with some added bisulfite, and known as the Zialite bath, has been in small scale use for many years. It is used to plate directly and protect intricate zinc base castings such as spray guns, because of its very good covering power. The pH of bath is usually kept at about 8 to 9 and temperature at about 35 oC. The plate is lustrous semibright and usually is not chromium plated.

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