Question

When a metal (M) is immersed in de-aerated acid electrolyte, it polarizes anodically by 0.4 V. The M/M\(^{n+}\) exchange current density is \( 10^{-5} \, \text{A m}^{-2} \) and Tafel slope is 0.1 V/decade for the anodic reaction. Assume that corrosion is uniform and anodic and cathodic reactions are under activation control. The rate of metal dissolution in A m\textsuperscript{-2 is \(\underline{\hspace{2cm}}\) (round off to 1 decimal place).}

Hint:

For metal dissolution, use the equation \( i = i_0 \exp\left( \frac{V}{\eta} \right) \) to calculate the dissolution rate.

Answer 1

Correct Answer: 0.1

The rate of metal dissolution is governed by the following equation:
\[ i = i_0 \exp\left( \frac{V}{\eta} \right) \] Where:
- \( i_0 = 10^{-5} \, \text{A/m}^2 \) (exchange current density),
- \( \eta = 0.4 \, \text{V} \) (polarization).
Substituting the values into the equation:
\[ i = 10^{-5} \times \exp\left( \frac{0.4}{0.1} \right) = 10^{-5} \times \exp(4) = 0.1 \, \text{A/m}^2 \] Thus, the rate of metal dissolution is approximately \( 0.1 \, \text{A/m}^2 \).