THE POINT-DEFECT MODEL FOR THE PASSIVE STATE

A review is presented of the point defect model (PDM) for the growth and breakdown of passive films on metal and alloy surfaces in contact with aqueous solutions. The model provides a reasonable account of the steady-state properties of cation-conducting and anion-conducting barrier layers on nickel and tungsten, respectively, in phosphate buffer solutions; of the impedance characteristics of passive films on nickel; of the breakdown of passive films on a wide range of metals and alloys; of the distributions in the breakdown parameters (breakdown voltage and induction time); of the role of alloying elements in enhancing the resistance of alloys to passivity breakdown; of transpassive dissolution and electro-polishing; of erosion-corrosion; and of photoinhibition of pit nucleation. Additionally, the PDM has allowed us to formulate a set of principles for designing new alloys and has led to the development of a deterministic method for predicting localized corrosion damage functions.