Sahithyan's S1 — Properties of Materials

Degradation of Metals

Corrosion

Deterioration of metals due to the reaction with the environment.

All corrosion reactions are electrochemical in nature.

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

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

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

The site at which oxidation takes place.

The site at which reduction takes place.

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

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

When 2 electrodes are electrically connected. The metal with the least $E^0$ becomes the anode.

Absolute difference between the 2 electrode’s standard electrode potentials. Denoted by $\Delta E^0$ .

For a corrosion reaction to occur spontaneously, $\Delta E^0 \gt 0$ . Cell potential is an approximate indication of the rate of corrosion.

\ce{ 2H^{+} + 2e^{-} -> H2 }

\ce{ O2 + H2O + 4e^{-} -> 4OH^{-} }

\text{Anodic}: \ce{ Zn -> Zn^{2+} + 2e }

\text{Cathodic}: \ce{ 2H^{+} + 2e -> H2 }

\text{Anodic}: \ce{ Fe -> Fe^{2+} + 2e }

\text{Cathodic}: \ce{ 1/2 O2 + H2O + 2e -> 2OH^{-} }