Basic Process of Electroplating
Electroplating is the deposition of a metal onto a metallic surface
from a solution by Electrolyses process. It is used for purpose of
decoration and protection of the metal. Metals commonly use to plate
surface are silver, chromium, cadmium, zinc, gold and copper. In the
case of copper platting for example electroplating takes place by means
of the reaction of Cu++ + 2e <====> Cu. Cu++ in this equation
represent an ion that is carried to the metal surface to be plated,
known as the CATHODE, from the source of the metal being plated, known
as ANODE. The ion forced to the cathode by an external source such as a
battery. The electrolytic solution is a salt of the metal being plated; in the case of copper plating. It is copper sulfate, CuSO4.5 H2O.
The
appearance, adhesion, porosity, and protection value of electroplated
coatings depends on several things, including the type of base metal be
plated, the preparation of the metal to be plating, and the
electrodepositing process itself.
Base Metal It is not possible to apply high quality coatings to metals of poor quality. The composition
of the base metal is usually known and controlled. The condition of the
surface, including the degree and nature of the polishing processes,
may also have a direct bearing on the characteristic and porosity of the
coating.
Preparation for PlatingIt is
necessary to have the base metal surface chemically clean in order to
secure good adhesion of deposits. The preparation usually involve
cleaning that is, removal of grease and foreign particles and picking in
the case of steel, or remove oxides or other compounds, and is some
instances, to etch the surface. Because of a thin, natural oxide film,
aluminum alloys do not usually respond to the cleaning and surface
preparation treatments employed for other metals; special techniques
must be used for such alloys.
Electrodeposition
In the plating process many
variables are involved that are subject to control. The composition and
temperature of the electrolytic bath itself must be closely maintained.
Agitation of the bath often permits an increase in current density.
Filtration, either continuous of intermittent, is often used to keep the
solution free of suspended matter. The average current density should
be kept within desired limits for the sake of uniformity in thickness
and quality of coating.
Finally, the anodes should ordinarily be
of such composition and structure as to maintain the metal concentration
and the pH. Where insoluble anodes are used, the metal content is
maintained by replenishment.
Most commercial plating with potentials
of conducted with motor generator sets, usually with potentials of from 6
to 12 volts, and with current outputs, depending on the area of work to
plated and the current density.
