Passivity of Metals and Alloys

Abstract

The sections in this article are Introduction Electrochemical Characteristics of Passive Systems Current–Potential Curves Thermodynamic Aspects of Passivity Potential Drops at the Passivated Surface Chemical Composition and Thickness of Passive Films on Metals Iron Nickel Chromium Copper Anodic Films on Aluminum Electronic Properties of Passive Films Structure of Passive Films Growth Mechanisms Effects of Alloying Elements Chromium Enrichment in Passivated Iron‐Based and Nickel‐Based Alloys Structural Aspects of Chromium Enrichment in Passive Films on Stainless Steels in Aqueous Solution: Aging Effects The Effects of Molybdenum The Effects of Nitrogen The Effect of Tungsten Passivity of Aluminum Alloys Alloying Elements as Passivity Promoters and Dissolution Moderators Detrimental Effects of Material Impurities: Sulfur‐Induced Corrosion Passivity Breakdown and Initial Stages of Pitting Phenomenology of Pitting Mechanisms of Pit Initiation Conclusions

Additive manufacturing – a general corrosion perspective

“…The oxide is, furthermore, chemically and most-likely structurally different from the usual native oxide. The oxide is protective if it is dense and well-structured without any defects or with low defect density, sustaining also low in ionic as well as electronic conductivity [13,14]. However, the ‘rapid’ manufacturing (quenched melted surface) is associated with a large in-built dislocation density which may be similar to highly deformed microstructures.…”

Passive film characterisation of duplex stainless steel using scanning Kelvin probe force microscopy in combination with electrochemical measurements

“…The bulk chemical composition of the two phases are different, and ferrite is typically rich in Cr and Mo while austenite is rich in Ni, Mn and N, resulting in usually higher corrosion potentials for the austenite than the ferrite. 20,21 Ni is known to propel Cr and Mo towards the outermost surface, 5,22,23 which may further explain the higher nobility (and also the nobler corrosion potential) of the austenite than that of the ferrite despite its lower bulk concentrations of Cr and Mo (Fig. 1).…”

“…26 The passive film of stainless steels is known to be composed of an outer iron-rich oxide, mainly Fe 2 O 3 and Fe(OH) 2 /Fe(OH) 3 , and an inner chromiumrich oxide, often stated as Cr 2 O 3 and Cr(OH) 3 , with also some molybdenum as well as silicon species. [22][23][24]27 The composition and morphology as well as defect contents and semiconductor properties of passive films of stainless steel can largely differ depending on the environment in which they form. In earlier work, it was shown that the native passive film on the studied alloy gets more defective upon anodic polarisation from its passive to transpassive potential regime in 1 M NaCl solution, and becomes thicker and changes its composition and structure.…”

“…6 Marcus et al reported passive films of stainless steels to be amorphous at the onset of oxidation and becoming crystalline by time. 23,28,29 It is therefore likely that the passive film after immersion in nitric acid became amorphous but had the tendency to transform to a crystalline structure as indicated by the change of the Volta potential by time. The passive film after the nitric acid treatment was imperfect, and some reconstruction processes governed the Volta potential changes.…”

Adsorption layers and passive oxide films on metals

“…[1][2][3][4][5][6][7] Detailed understanding of tribocorrosion properties of passivated metals requires not only a good knowledge of the composition and structure of passivated surfaces and their dissolution mechanism in the absence of the second body but also a clear understanding of the behavior of metal surfaces in the active state and of the modifications generated by ion adsorption and by the active/passive transition. The topics addressed in this chapter include the adsorption of salt ions from the electrolyte and its influence on the dissolution of metal surfaces in the active state, the adsorption…”