Finishers Think Tank

by

Marty Borruso

26 Flagship Circle

Staten Island, NY 10309

Phone: 1/800-366-5065

Originally Published in:

PLATING AND SURFACE FINISHING

Journal of the Electroplaters and Surface Finishers Society

February 1994

Topic: Watts Nickel Plating

The Watts nickel plating process is probably the most common type of plating solution in North America. It is a versatile

system and useful in many industries and applications. Nickel deposited from Watts baths contributes to corrosion protection or is used just for the decorative purpose of providing a bright, leveled deposit on many substrates. The components of a Watts system vary in concentration, depending on the application, to yield differing results. But for all intents and purposes, they are usually within the following ranges:

Nickel Sulfate

Nickel sulfate is used to provide the nickel metal reserve in the plating bath. Nickel sulfate is common; relatively inexpensive; and it imparts few problems, such as stress, to the deposit as compared to other forms of nickel-bearing materials.

Nickel sulfate is used in concentrations from 10-40 oz/gal.

Nickel Chloride

Nickel chloride is used in the Watts bath to help increase the anode efficiency of the process system. By increasing the anodic efficiency, organic materials are less likely to be oxidized at the anodes and form potentially harmful by-products. Nickel chloride also allows for deposit of nickel at reasonably low current density areas. This material will also allow operation of the Watts system at reasonably low temperatures and also allow operation with a significant concentration of contaminants in the plating bath.

Nickel chloride is used in concentrations from 6-40 oz/gal, depending on the process substrate and the methodology of operation. When fuel costs are high, there is a tendency to run chloride levels higher, because the trend is to run plating baths at lower temperatures. To accomplish this, the nickel chloride concentration is kept at higher levels.

Boric Acid

Boric acid is used in the Watts plating bath because of its action as a buffering agent, and its reaction as a multihydric acid material. It also provides a buffering action within the solution surface interface area of the catholyte film.

Boric acid is used in concentrations from 5-7.5 oz/gal.

Other significant operating parameters of Watts plating solutions are:

If you operate a Watts bath within these parameters, you should be reasonably successful. The most important factor in operating a Watts nickel bath is keeping the bath clean and free from organic and metallic contaminants.

Most Watts formulations are operated with the inclusion of proprietary additives, and consultation with suppliers of those additives is important to get the appropriate results. Work with them to specify the proper formulation for the finish you wish to produce. But beware of materials that are touted as "purifiers," or that will allow you to operate at high levels of contamination. The most effective and efficient method of dealing with contaminants is not to have them in the bath in the first place. These "purifiers" usually sacrifice something in leveling or brightening of the deposit.

Agitation

Agitation is a very important part of the operation of a Watts nickel solution so much so that I will include it as a component of the process system. The use of air or mechanical agitation is important, because the catholyte film on the deposited surface tends to deplete metals from the catholyte film. The pH of the film changes rapidly, so the film must be replenished rapidly. Higher current densities are possible when the agitation is rapid and the solution interface changes at a high rate. Air agitation is the most frequently used method employed by modern

electroplaters, but solution sparging and mechanical movement of parts are also popular.