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2. Contact corrosion
Corrosion is accelerated in situations where
an electrochemically “less noble” material is
in contact with a “noble” material. The material
loss of the noble partner is reduced, the
loss of surface area of the less noble partner
is increased. A prerequisite for this form of
corrosion is an electrically conductive connection
between these two materials.
Surface area ratio
Whether or not contact corrosion occurs
also depends on the surface area ratio.
A)
If the surface of the less noble material (1) is
greater than that of the more noble material
(2), it will act as a very small cathode and the
current density on the “large anodic” less
Two materials of different resistance/
polarity exposed to the same media,
not in direct electrical contact
Material 1 Material 2
in direct electrical contact
Material 1 Material 2
Corrosion
A Starting level
B 1 , B 2 Reduction of the thickness depending on the
material's resistance
noble material is thus very small. Furtherermore,
this also implies a very low rate of
corrosion of the less noble metal due to
electrochemical effects.
B)
However, if the surface of the less noble
material is smaller than that of the more
noble material, the rate of corrosion of the
less noble metal will be very high.
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