CHMT3027A: Corrosion Thermodynamics and Kinetics

Flashcards covering the thermodynamic and kinetic principles of corrosion, including Gibbs Free Energy, Nernst equations, Pourbaix diagrams, and Faraday's Law.

Gibbs Free Energy ($\Delta G$)

A thermodynamic value used to predict if a corrosion reaction is possible; corrosion occurs spontaneously when $\Delta G < 0$.

Faraday's constant ($F$)

A constant used in electrochemical calculations, defined as $96\,500\,\text{J/v} \cdot \text{mol e}^-$ or $96\,500\,\text{C/mol e}^-$.

$n$ (in $\Delta G = -nFE$)

The number of electrons transferred in an oxidation reaction (measured in $\text{mol e}^-$).

Strongest oxidizing agent

According to the standard electrode potential table, it is $\text{F}_2(g)$ with a value of $2.87\,\text{v}$.

Strongest reducing agent

According to the standard electrode potential table, it is $\text{Li}(s)$ with a value of $-3.04\,\text{v}$.

Standard electrode potential of Iron ($\text{Fe}$)

For the reaction $\text{Fe}^{2+}(aq) + 2e^- \rightarrow \text{Fe}(s)$, the value is $-0.45\,\text{v}$ ($E_{\text{ox}}^0 = 0.447\,\text{v}$).

Standard electrode potential of Zinc ($\text{Zn}$)

For the reaction $\text{Zn}^{2+}(aq) + 2e^- \rightarrow \text{Zn}(s)$, the value is $-0.76\,\text{v}$.

Standard States

The reference conditions for electrochemical calculations, defined as unit activity, pressure of $1\,\text{atm}$, and a temperature of $25^{\circ}\text{C}$.

Nernst Equation

An equation used to calculate electrode potential at non-standard states: $E = E^0 + \frac{0.059}{n} \cdot \log\left(\frac{(A)^a}{(B)^b}\right) - \frac{m}{n} \cdot 0.059 \cdot \text{pH}$.

Pourbaix Diagrams

Schematic illustrations that predict the stability of materials in specific $\text{pH}$ and potential ranges, where boundary lines are derived from the Nernst equation.

Areas of immunity

Regions on a Pourbaix diagram where reduced species are stable.

Areas of passivation

Regions on a Pourbaix diagram where oxides and hydroxides are stable, potentially forming a protective film.

Areas of corrosion

Regions on a Pourbaix diagram where soluble species are stable.

Faraday’s Law (Mass loss)

The relationship used to determine material consumption over time: $m = \frac{I \cdot t \cdot a}{n \cdot F}$, where $m$ is mass loss, $I$ is current, and $t$ is exposure time.

Corrosion Rate

A measure of how fast a material degrades, determined by the rate of electron flow in electrochemical reactions.

Cathodic reaction (Aerated acid)

The reduction reaction occurring in aerated acid solutions: $4\text{H}^+ + \text{O}_2 + 4\text{e}^- \rightarrow 2\text{H}_2\text{O}$.

Cathodic reaction (Deaerated acid)

The reduction reaction occurring in deaerated acid solutions: $2\text{H}^+ + 2\text{e}^- \rightarrow \text{H}_2$.