Passivity of Iron-A review

Abstract

The passive film on iron has provided positive benefits to the longevity of iron structures since antiquity. As the benefits of passivity of iron became recognized, debates among scientists developed over the possible mechanisms by which the very thin (2-3 nm) passive layer could impart substantive corrosion resistance. The mechanisms of passivity that impart unique properties to passive iron have been studied and debated for decades. In recent years, equipment that is sufficiently advanced for surface studies at an atomic level has been used to explore the mechanisms of passivity and, in combination with electrochemical studies, to characterize the chemical composition, physical structure, and electronic properties of the passive film on iron. The evolution of the concepts and theories of the passivity of iron are reviewed in this paper, beginning with the earliest observations and summarizing the developments that have become possible as a result of advances in instrumentation and surface analytical methods. Effects of temperature, texture, and hydrodynamics on the mechanisms of passivity of iron are discussed.