Physics-Chemical Aspects of Corrosion

From a general point of view besides the alloy composition and metallurgical structure, the most important physics-chemical parameters that control SCC are fundamentally five  

Their influence on SCC is very complex and can be generally expressed in terms of penetration depth versus time through an equation of the type 

In which is the variation of the Gibbs free energy relative to the passage from the first chemical species to the second, R is the ideal gas constant equal to 8.3144 J/(mol K) or 1.987 cal/(mol K), T the absolute temperature and K the equilibrium constant of the specific reaction. The equilibrium constant of a reaction involving two (or more) species A and B that react to form two new species C and D is a number that represents the ratio between the product of the concentrations or moles per liter of the two final species to that of the initial species, each to the power of the stoichiometric factor c, d, a and b of the chemical reaction 

The electrochemical reactions or redox reactions are defined by the Nernst equation 

10) the term RTInF InK is a constant for any given temperature and will be indicated as so that at ambient temperature (K = 298) taking the water concentration equal one, Eq. (13.10) becomes 

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