Fundamentals of Electrochemistry
This chapter aims to give the basic knowledge needed to interpret electrochemical corrosion. Metals ranked in their order of reactivity are said to be in an electrochemical or galvanic series, and such rankings, different for different environments, are important in predicting corrosion of "galvanic" couples between dissimilar metals. It is possible for the anodic and cathodic reaction sites on a corroding metal surface to be permanently separated on either a microscopic or macroscopic scale and this produces localized corrosion. Localized corrosion can be caused by deposits on a metal surface that create the different oxygen availability. Uniform attack occurs evenly over the whole metal surface, whereas localized corrosion may take the form of pitting or crevice corrosion, corrosion fatigue, impingement, and fretting corrosion. Stress corrosion cracking and corrosion fatigue are forms of localized attack characterized by the combined action of tensile stress and corrosion. Under the circumstances prevailing in corrosion reactions, the metal dissolution reaction always shows charge-transfer polarization.