CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 4
(Ag/AgCl). The platelets formed were very few, and the surface dissolution occurred on brighter
regions of the surface which are the topographically elevated portions on the surface (Fig. 4.8d)
[20].
a
c
d
Fig. 4.8: In-situ surface morphology of 304L SS in 0.6 M nitric acid (a) as polished, (b) 500 mV,
(c) 900 mV and (d) 1100 mV vs. Ag/AgCl [20].
Figure. 4.9a-d represents the surface morphology of 304L SS under immersion condition in 1
M nitric acid in as polished, 500 mV (Ag/AgCl), 900 mV (Ag/AgCl), and 1100 mV (Ag/AgCl),
respectively. In 1 M HNO 3 , the morphological features were different from other concentrations as
formation of platelet like structure was not observed. Instead the grain boundaries opened up
slowly with increase in potential showing well defined boundaries around 1100 mV (Ag/AgCl)
(Fig. 4.9d). This is due to increase in oxidizing power of nitric acid owing to higher auto-catalytic
activity which preferentially attacks the heterogeneous oxide boundaries [20].