Critical review on the passive film formation and breakdown on iron electrode and the models for the mechanisms underlying passivity

Iron and its alloys acquire stability because of the phenomenon of passivity. Though several theories, models and experimental works on passivity have been published in the literature, the mechanisms underlying the stability of the passive oxide over the metals remain still a mystery. This review presents recent developments on theoretical and experimental results besides the literature available in other reviews and critically review selected experimental results on iron/electrolyte system and theoretical developments in general and specific to iron by invoking high field model, modified high field model, point defect model (PDM), variants of PDM (VPDM), diffusion Poisson coupled model (DPCM), density functional theory based atomistic model. The experimental and model-predicted dependencies on applied voltage, pH, chloride and temperature are also presented and discussed.