CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 5
F/cm 2 with highest dose of nitrogen indicating better passive film stability. Thus, in general with
increasing dose of nitrogen ion implantation increase in the stability of the passive film was
observed as compared to unimplanted condition [21].
N + Dose
R S
(ohm)
R P
(ohm cm 2 )
C dl
(F/cm 2 )
AISI 304L SS 5 1675 1×10 -5
1×10 15 N + /cm 2 5 2223 1×10 -6
1×10 16 N + /cm 2 5 2690 1×10 -6
1×10 17 N + /cm 2 7 4970 1×10 -7
2.5×10 17 N + /cm 2 7 7085 1×10 -8
Table. 5.2: EIS fitted values of unimplanted and nitrogen implanted 304L SS in 1 M HNO 3 [21].
The ennoblement observed in polarization resistance is due to stable and readily passive
film formation because of presence of interfacial nitrogen at lower doses, and due to formation of
chromium nitride at higher doses. At lower doses, nitrogen is present in solid solution gets
enriched in passive film by bonding with chromium and thereby enhances passive film stability
[168]. The implanted nitrogen can also accumulate at the surface inhomogenities such as surface
defects and kinks making the passive film homogenous [166]. At higher doses presence of
chromium nitride provides rich supply of chromium due to high chromium content in nitrides for
oxide film formation [166].
The corrosion behaviour of stainless steels is often correlated to the protective nature of the
passive oxide film, which forms on the surface. If one takes the reasonable view that corrosion
initiate at flaws in the film or substrate (inclusions), then one can argue that the surface film
composition will directly reflect corrosion resistance of the alloys. Based on the present results,