CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 4
pitting, and intergranular corrosion of 304 SS in NaCl and oxalic acid medium. Zhang et al [118]
have reported that the current density for pit growth is higher as compared to that of applied
current on the analysis of the role of corrosion products on pitting corrosion of SUS 304 SS.
Femenia et al [119] have shown that potential for the dissolution of austenite phase is higher as
compared to ferrite phases on the investigation of surface dissolution process of 2205 duplex
stainless steel in H 2 SO 4 and HCl medium. Martin et al [120] have reported the initiation of the pits
is along the ridged lines as a result of strain hardening due to mechanical polishing on the
investigation of pitting corrosion of 304L SS in chloride media. However, to date no ex-situ or insitu
study has been carried out to understand the passive film properties of austenitic stainless steel
in nitric acid medium which is mostly related to the corrosion resistance of stainless steel in
nuclear fuel reprocessing environment.
The scope of the chapter is to understand the passive film morphology of 304L SS in nitric
acid medium in both ex-situ and in-situ conditions with increase in concentration. The
concentrations of nitric acid used in ex-situ, and in-situ study are different because process
conditions have to be simulated, and experimental difficulties should be taken care. Thus for exsitu
study higher concentration, and for in-situ study lower concentration of nitric acid were used.
Overview of the present investigation includes, (a) examining the time-dependent morphological
changes of 304L SS in 1 M, 4 M, 8 M, and 11.5 M nitric acid after different hours of exposure
using atomic force microscope, (b) analysis of polarization behaviour of 304L SS in 0.1 M, 0.5 M,
0.6 M, and 1 M nitric acid, (c) realizing the morphological changes according to polarization
study using in-situ electrochemical atomic force microscope (EC-AFM), and (d) analyzing the
chemical composition of the passive film as observed in in-situ study in 0.1 M, 0.5 M, 0.6 M, and 1
M nitric acid by using X-ray photoelectron spectroscopy.