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.