A review of passivity breakdown on metal surfaces: influence of chloride- and sulfide-ion concentrations, temperature, and pH

Metals, including austenitic steels and alloys, have been extensively applied in industrial and engineering applications. Passive films on metal surfaces are very important for corrosion protection. However, localized attack, such as passive film breakdown and the initiation of pits, is found upon exposure of such metals to aggressive ion-containing environments, leading to material failure and prominent adverse economic and safety concerns. For several decades, the mechanism of passivity breakdown and pit nucleation during pitting corrosion has been widely studied. The present article provides a detailed review of passive film breakdown on metal surfaces and the effects of complicated conditions, such as chloride- and sulfide-ion concentrations, temperature, and solution pH, on passivity breakdown. The possible mechanism for passivity breakdown is reviewed and discussed. The composition, structure, and electronic properties of passive layers are of conclusive importance to understand the leading corrosion mechanism, and they have been investigated with different techniques. Furthermore, we aim to present the structure, chemical composition, and electronic properties of passive films on metal surfaces by using X-ray photoelectron spectroscopy and energy-dispersive spectroscopy. Additionally, the surface morphology of passive films is analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) techniques. Finally, the effect of chloride- and sulfide-ion concentrations, pH, and temperature on passivity breakdown is discussed in detail.