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.