CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 4
Considerable progress have been made in the recent past towards understanding the nature
of passivity with the development of optical, electro-optical, in-situ electrochemical, and
morphological analysis equipments. Out of several important physico-chemical properties, surface
morphological evidences are critical for understanding the passive film properties such as, growth
of oxide film, possible pre-cursor sites for localized dissolution of passive film, physical changes
occurring during the breakdown of passive film, and the transport process occurring over the
surface [116]. Dynamic observations of the above surface morphological features in real condition
are quite helpful in understanding the nucleation and growth of passive film at nano-scale, aging
with increase in thickness, and the manner by which passive film breakdown occurs on the
surface. Similarly, the propagation of corrosion is a surface phenomenon, and without substantial
knowledge of surface morphological features it is difficult to fully understand the process of
corrosion. Thus, the conceptual understanding on the surface morphological features is
indispensable for understanding applied aspect of corrosion science.
Recent development of in-situ surface monitoring systems such as scanning probe
microscope has opened up a new scope and dimension for understanding localized corrosion
phenomenon, as it provides information regarding structural and electrochemical phenomenon
occurring in a simulated electrochemical environment [112]. Considerable attempts have been
made to comprehend the phenomenon of localized corrosion in stainless steel in various
electrochemical environments using in-situ scanning probe microscope technique. Kamachi
Mudali and Katada [11] have investigated the nano-mechanical properties of passive film of
nitrogen-bearing austenitic stainless steel, and have predicted the decrease in stiffness value and
increase in height of passivated surface in 0.5 M NaCl medium under different surface conditions.
Williford et al [117] have demonstrated the growth of pit over time, and initiation of intergranular
corrosion between grain boundaries adjacent to chromium carbide precipitate on the study of