What is cathodic protection

Experiment: Demonstration of cathodic corrosion protection using a sacrificial anode
Experiment: The stainless iron nail or the sacrificial anode

Cathodic corrosion protection is used wherever metal parts are under water or underground, such as B. in pipelines, ship hulls, boilers and storage tanks.

With cathodic corrosion protection, the piece of metal to be protected is electrically connected to an anode made of a base metal (e.g. magnesium) (-> experiment). The anode is also called Sacrificial anodebecause it dissolves over time.

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Sacrificial anodes. Above is a used, but still fully functional anode.
Below an unused anode before installation
(Photo: flower)

(There is also a tip of the month February 1998 on this subject: "The stainless iron nail or the sacrificial anode").
This creates a galvanic element. The water or the soil acts as the electrolyte. When using a magnesium anode, the following reaction occurs:

Mg à Mg2+ + 2 e-

The electrons flow to the cathode and prevent its corrosion by shifting the equilibrium of the following reaction:

Metal à metaln + + n e-
metaln + + n e-à metal

The electrons arriving at the cathode shift the equilibrium in the direction of the metal. The metal is therefore not oxidized. However, metal objects can be protected from corrosion not only with a sacrificial anode, but also with negative charging with negative (`` cathodic '') external current (direct current) (-> experiment). The latter is often cheaper and, above all, more convenient than constantly changing a metal rod.

Further texts on the subject of electrochemistry