Cathodic Reactions in Corrosion

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The kinetics of the cathodic reactions often determines the corrosion rate of a metal or alloy in an aqueous electrolyte. The primary cathodic reactions in aqueous corrosion are listed below.

Proton reduction reaction (acids)

$$2{H^ + } + 2{e^ - } \leftrightarrow {H_2}(g) \tag{1} \label{eq:1}$$

Water reduction reaction (bases)

$$2{H_2}O + 2{e^ - } \leftrightarrow {H_2}(g) + 2O{H^ - } \tag{2} \label{eq:2}$$

Oxygen reduction reaction (acids)

$${O_2}(sol.) + 4{H^ + } + 4{e^ - } \leftrightarrow 2{H_2}O \tag{3} \label{eq:3}$$

Oxygen reduction reaction (bases)

$${O_2}(sol.) + 2{H_2}O + 4{e^ - } \leftrightarrow 4O{H^ - } \tag{4} \label{eq:4}$$

Equivalnet reactions

Equations $\eqref{eq:2}$ is equivalent to $\eqref{eq:1}$ and $\eqref{eq:4}$ to $\eqref{eq:3}$, assuming dissociation of water to $H^{+}$ and $OH^{-}$ and subtracting $OH^{-}$ from both sides.

References

D.A. Jones, "The Technology and evaluation of corrosion," in Principles and Prevention of Corrosion, 2nd ed., (Upper Saddle River, NJ: Prentice-Hall, 1996), p.5-9. ISBN: 0-13-359993-0. Buy at Amazon