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Degradation of Metals

Corrosion

Deterioration of metals due to the reaction with the environment.

All corrosion reactions are electrochemical in nature.

Electrochemical reactions

Pair of reactions in which electron transfer occurs from one reaction to another.

Oxidation

The reaction where an electron is released. Aka. anodic reaction.

Reduction

The reaction where an electron is consumed. Aka. cathodic reaction.

Electrodes

Anode

The site at which oxidation takes place.

Cathode

The site at which reduction takes place.

Standard Electrode Potential

Measure of a metal’s ability to work as a anode or cathode. Measured in reference to hydrogen. Denoted by .

Electrochemical series

A series of pure metals in the order of their standard electrode potential. Alloys and other materials are not listed.

Cell

When 2 electrodes are electrically connected. The metal with the least becomes the anode.

Cell potential

Absolute difference between the 2 electrode’s standard electrode potentials. Denoted by .

For a corrosion reaction to occur spontaneously, . Cell potential is an approximate indication of the rate of corrosion.

Common reactions

Hydrogen evolution reaction (HER)

Oxygen reduction reaction (ORR)

Examples

Zn in acid

Fe rusting in atmosphere