CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 5
electrochemical environment, nitrogen present at the surface forms ammonium ion which buffers
the local pH, and enhance the passivation property [165]. According to study carried out by
Newman et al [166], nitrogen enrichment on the surface can block the kinks and defects, making
the surface homogenous, and forming uniform passive film over the surface. At higher doses the
formation of chromium nitride also improves the passive film stability by forming rich oxide
layer, and ammonium ions [166]. However, OCP gives only an initial indication of passive film
behaviour, its actual stability in aggressive environment can be better understood from
electrochemical perturbation conditions.
0.4
Potential (V) vs Ag/AgCl
0.3
0.2
0.1
0.0
-0.1
304L SS
1 x 10 15 N + /cm 2
1 x 10 16 N + /cm 2
1 x 10 17 N + /cm 2
2.5 x 10 17 N + /cm 2
-0.2
0.0 5.0x10 3 1.0x10 4 1.5x10 4 2.0x10 4
Time (Sec)
Fig. 5.6: OCP of unimplanted and nitrogen ion implanted 304L SS in 1 M HNO 3 [21]
5.2. 7 Potentiodynamic polarization study
The potentiodynamic anodic polarization results for the unimplanted, and nitrogen
implanted 304L SS in 1 M HNO 3 are depicted in Fig. 5.7 [21]. The polarization plots for both