CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 5
layer capacitance (C dl ), polarization resistance (R p ), and solution resistance (R S ) are as shown in
Table. 5.2 [21].
-14000
-12000
-10000
304L SS
1x10 15 N + /cm 2
1x10 16 N + /cm 2
1x10 17 N + /cm 2
2.5x10 17 N + /cm 2
-Z''(Ohm cm 2 )
-8000
-6000
-4000
-2000
0
0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000
z'(Ohm cm 2 )
Fig. 5.8: Electrochemical impedance of unimplanted and nitrogen implanted
304L SS in 1 M HNO 3 [21].
In impedance measurement, high R p value implies good corrosion resistance, and the low
capacitance value signifies long term stability of the passive film. A comparison of Nyquist plots
between unimplanted, and implanted with different doses of nitrogen revealed better passive film
stability with nitrogen implantation owing to improvement in polarization resistance, and decrease
in double layer capacitance. The polarization resistance increased from 1675 Ohm cm 2
in
unimplanted condition to 7085 Ohm cm 2 at highest dose of nitrogen implantation. Similarly, the
double layer capacitance showed a reduction in total retained charge from 1×10 -5 F/cm 2 to 1×10 -8