CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 6
The high phase angle over wide frequency region for TiO 2 coated specimens as compared
to uncoated, and Ti coated specimens is due to their capacitive property as well as high resistance
to current flow in coated surface owing to insulating nature [22]. Similarly, the plot of Log f vs.
Log |Z| of 304L SS at lower concentration (1 M) showed two frequency independent horizontal
regions in low and high frequency region, and capacitive behaviour at intermediate frequency in
middle region (Fig. 6.10b). As compared to uncoated specimens, TiO 2 coated specimens showed
two order increase in magnitude of total impedance (|Z|), and slope of -1 up to high frequency
region showing largely capacitive property. As compared to Ti coated specimens, the
improvement in magnitude of total impedance was one order of magnitude (Fig. 6.10b)
Fig. 6.10b: Log f vs. Log |Z| for uncoated and TiO 2 coated 304L SS in 1 M HNO 3 [22].
However, the TiO 2 coated specimens exhibited two time constant feature in 8 M nitric acid
[203] indicating change in passive film property at higher concentration (Fig. 6.10c). The two time