Nickel is one of the most important electroplated metals in the Detroit area. It is the foundation for most chrome auto parts, as well as household items ranging from tape measures to toaster ovens. There are primarily three types of nickel solutions: bright, semi-bright, and high-sulfur strike. Bright nickel is lustrous with a yellowish-brown color to the metal, while semi-bright is characterized by a grey haze. High sulfur nickel is also grey and hazy.
When a steel bumper is nickel plated, it is first cleaned and then usually electrocleaned (running a current through the part while it is immersed in cleaning solution). This charges dirt particles and expels them from the metal. The nickel is then given a layer of semi-bright nickel for corrosion resistance and as a foundation for further layers. The metal is rinsed and then a high-sulfur strike is deposited. This is a thin coat of nickel with a high sulfur content, which rusts very easily. This way, if the outer layers rust through, the rust begins to oxidize the high sulfur strike layer and doesn't attack the underlying steel. The metal is then rinsed again, and a layer of bright nickel is deposited. This also serves as corrosion protection and is the base for a chrome deposit. After a rinse, the nickel is dipped in a chromic acid solution, then chrome plated to produce a finished bumper.
For appliances, the process is much simpler. The metal is cleaned and sometimes electrocleaned then covered with a nickel coating. After a rinse, chrome is deposited. For plastic parts, an electroless copper is usually deposited, after which the part is nickel plated and finally chrome plated.
Nickel solutions are robust, and can handle a wide range of conditions and salt concentrations, but periodic measurements must be made to ensure a bath is within the operating boundaries. Tests are run on salt content, boric acid content, and carrier and brightener contents. A test panel is also run in a Hull cell to look for problems over a wide range of current densities.
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This page last updated on 11/7/96.