E-8
ElektroPhysik
2. Introduction
2.1 General Usage and measuring principle
The coulometric or electrochemical de-plating technique
according to DIN 50955 / ISO 2177 is suitable for the
measurement of electroplated coatings on practically all
substrate materials, i.e.: on steel, on non-ferrous metals
and also on insulating materials, e.g. nickel on steel,
zinc on steel, tin on copper, silver on copper and copper
on epoxy.
This method is also suitable for measuring the individu-
al coatings of multi-layer systems such as chrome on
nickel on copper on steel.
The measuring principle is based on Faraday’s Law. The
opposite of the electroplating method applies, the coating
being electro-chemically removed from the sample.
On this purpose, a stainless steel measuring cell is
placed on the sample to be measured. The cell is filled
with an electrolyte solution which is selected according
to the coating / base combination. A rubber gasket placed
between the cell and the sample defines the area of
measurement, e.g. 4 sq. mm. The measuring set-up is
electrically connected to the electronic processing unit.
When switched on, a constant current flows through the
electrolyte to remove the metallic coating electro-
chemically.
Throughout the entire de-plating process, a defined
voltage can be observed between measuring cell and
object to be measured. As soon as the metallic coating
has been completely removed, a characteristic voltage
jump occurs. This voltage jump is registered by the
measuring gauge to interrupt the voltage supply and to
stop the timer. Thickness is immediately displayed in
mils or microns.
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U
Measuring cell
Elektrolyt
Rubber
gasket
Measuring
area
Coating
Substrate
material
Electro-
lyte