POLARIZATION OF A GALVANIC CELL

Example 5.1 Determine the overpotential and free energy change profiles as functions of the reaction constant at varying temperature. Explain the electrochemical behavior. 

The figures below show the required profiles for E = f (K, T) and t] — F K,T) in two dimensions Succinctly, both overpotential and free energy change are very sensitive to variations of both the reaction constant and temperature. 

When steady-state is reached the current densities and potentials become equal that is. 

It should be pointed out that the corrosion potential in the galvanic series (Table 2.3) and that in the emf series (Table 2.4) are not the same. The former may be measured as a coupled potential at different temperatures and ionic concentrations used in the latter series. Therefore, the galvanic series must be used with caution since it is ten )erature and concentration dependent kinetic parameter. 

The surface area of the electrode in the corrosive medium is known as the relative area, which influences the rate of galvanic corrosion. For instance, the experimental data on brass/steel couple in 20%NaCl at room temperature reported by Jones [19] can be used to determine that increasing the surface area ratio increases the the galvanic corrosion potential. Therefore, the corrosion potential of galvanic couplings is strongly dependent on the cathode-to-anode surface area ratio. 

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