ABSTRACT
Corrosion of metal materials is classied, in terms of environmental conditions, into either wet or dry corrosion. is subsection focuses on wet corrosion. As stated earlier, stainless steels are iron-system alloys containing Cr as the principal alloying element with additional solute elements such as Ni. To understand the corrosion behavior of a metal material, it is important to understand the dissolution behavior of each of the alloying elements. Wet corrosion occurs as a result of an electrochemical reaction. Generally, the reaction by which a metal (M) dissolves in an aqueous solution as an ion (Mn+) is expressed as follows:
M M ne n
= ++ − (6.1)
e Gibbs free-energy change ∆G of this equation is given as follows:
∆ ∆G G RT K= + 0 ln (6.2)
where ∆G0 is the standard Gibbs free-energy change R is the gas constant T is the absolute temperature K is the equilibrium constant for Equation 6.1
en, where F is Faraday’s constant and E is the electrode potential, −∆G is equal to maximum work nFE of the reaction.
