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CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

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Chapter 6<br />

showed steady improvement with increase in time, however transient points were observed prior<br />

to attainment of steady state which could be due to competitive passive film formation and<br />

dissolution at the few existing structural heterogeneities such as pinholes and inter-columnar<br />

boundaries causing increase in oxidizing ability.<br />

Fig. 6.14b: OCP vs. time measurement for uncoated and Ti-TiO 2 coated 304L SS in 8 M HNO 3 .<br />

6.2.3.3 Electrochemical impedance analysis<br />

The results of electrochemical impedance analysis for uncoated, and Ti-TiO 2 coated 304L<br />

SS in 1 M and 8 M nitric acid in OCP condition are shown in Fig. 6.15a-d. As mentioned earlier,<br />

the fitted graphs obtained using electrical equivalent circuit model as shown in Fig. 3.10a-b are<br />

also shown in Fig. 6.15a-d. The plot of phase angle () vs. frequency in 1 M nitric acid largely<br />

revealed near capacitive property in the entire frequency domain of investigation with one time<br />

constant feature which shows the formation of very stable passive film as well as resistance to<br />

alteration in property and initiation of anodic activities on the coated surface (Fig. 6.15a) [208].

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