SURFACE SCIENCE APPROACH OF CORROSION PHENOMENA

Authors
Citation
P. Marcus, SURFACE SCIENCE APPROACH OF CORROSION PHENOMENA, Electrochimica acta, 43(1-2), 1998, pp. 109-118
Citations number
26
Categorie Soggetti
Electrochemistry
Journal title
ISSN journal
00134686
Volume
43
Issue
1-2
Year of publication
1998
Pages
109 - 118
Database
ISI
SICI code
0013-4686(1998)43:1-2<109:SSAOCP>2.0.ZU;2-A
Abstract
This article presents a brief review of data on adsorption, anodic dis solution and passivation of well-defined single crystal surfaces of me tals (Ni, Cr) and alloys (stainless alloys), which exemplify the conce pt of surface science approach of corrosion phenomena. This approach a ims at a better understanding of corrosion phenomena at the atomic or molecular level. In the first part, the effects of sulphur, adsorbed o r segregated on the surface, on corrosion or passivation are described , including the sulphur-induced enhancement of dissolution and the blo cking of passivation. It is shown how the conditions of stability of a dsorbed sulphur monolayers can be predicted on thermodynamics grounds and this is illustrated by a potential-pH diagram for adsorbed sulphur on nickel in water at 25 degrees C. The next part of this paper deals with the structure and chemistry of thin oxide overlayers (passive fi lms), with special emphasis on recent data on the atomic structure of passive films obtained by scanning tunneling microscopy (combined with surface chemical analysis by X-ray photoelectron spectroscopy). The m ajor problems which are addressed are the crystallinity, the epitaxy a nd the nature of defects of passive firms, which are key factors in th e resistance to both general and localized corrosion. The recently obs erved structural modifications of passive films on stainless steels pr ovided by aging in aqueous solution are indicated (crystallization and coalescence of Cr2O3 islands). Finally, an attempt to rationalize the role of alloyed elements in terms of passivity promoters (elements th at enhance passivity) or dissolution moderators or blockers (elements that slow down the anodic dissolution rate) is described. The proposed model is based on a comparison, for different metals, of the tendency of the metal for oxygen adsorption (reflected in the heat of adsorpti on of oxygen) and the relative facility in disrupting metal-metal bond s (a necessary step in the transition between two-dimensional and thre e-dimensional oxide, leading to passivity. (C) 1997 Elsevier Science L td.