Electroless nickel is widely used in the metal finishing industry as a coating. It plates evenly on a variety of surfaces and replicates or enhances the surface finish. It has high hardness and good corrosion resistance and machinability. However, its bath life is limited and it has a tendency to spontaneously plate out on the tank and associated equipment. These problems add to the cost per unit component plated. Also, expensive waste treatment is required before users can dispose of the spent solution. Electroless nickel`s limited bath life is inherent in its chemical make-up. Using hypophosphite as the reducing agent …
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Publisher Info:
Lawrence Livermore National Lab., CA (United States)
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California
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Description
Electroless nickel is widely used in the metal finishing industry as a coating. It plates evenly on a variety of surfaces and replicates or enhances the surface finish. It has high hardness and good corrosion resistance and machinability. However, its bath life is limited and it has a tendency to spontaneously plate out on the tank and associated equipment. These problems add to the cost per unit component plated. Also, expensive waste treatment is required before users can dispose of the spent solution. Electroless nickel`s limited bath life is inherent in its chemical make-up. Using hypophosphite as the reducing agent for the nickel ion generates by-products of nickel metal and orthophosphite. When the level of orthophosphite in the solution reaches a high concentration, the reaction slows and finally stops. The bath must be disposed of, and its treatment and replacement costs are high. Metal salts have a tendency to plate out because of the dissolved solids present, and this also makes it necessary to discard the bath. Lawrence Livermore National Laboratory (LLNL) has conducted a study of an electrodialysis process that can reduce both chemical purchases and disposal costs. Electrodialysis employs a membrane, deionized water, and an electromotive potential to separate the orthophosphite and other dissolved solids from the nickel ions. With the aid of the electromotive potential, the dissolved solids migrate across the membrane from the process solution into the water in the recycling unit`s holding cell. This migration lowers the total dissolved solids (TDS) in the process solution and improves plating performance. The dialysis process makes it possible to reuse the bath many times without disposal.
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