Thermodynamics of Aqueous Corrosion

Abstract

This chapter addresses the thermodynamic aspects of corrosion, starting from the concept of free energy: indeed, corrosion can take place only if the free energy variation associated with the reaction is negative, i.e., the reaction is thermodynamically favoured. This translates in terms of variation of potential, outlined as driving voltage, or electromotive force, for the reaction. Standard potentials and equilibrium potentials of anodic and cathodic reactions are defined, together with conditions for corrosion and for immunity. Reference electrodes are presented, which allow to measure the potential as difference between a given electrode and a well defined reference electrode that has the property of maintaining its potential constant. Finally, electrochemical cells, as Daniell or concentration cells, are introduced.