CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 3
different doses of nitrogen (1×10 15 , 1×10 16 , 1×10 17 , 2.5×10 17 N + /cm 2 ) in 1 M nitric acid. Similarly,
OCP-time measurements for uncoated, titanium (Ti) titanium dioxide (TiO 2 ), and duplex Ti-TiO 2
coated 304L SS were carried out in 1 M and 8 M nitric acid, respectively. The solutions used in
the investigations were not de-aerated, and the specimens were immersed at least for 30 minutes
for attaining stability at the electrode-electrolyte interface. At least three tests were carried out to
check the reproducibility for various types of specimens examined in the present investigation at
different concentration of nitric acid.
3.1.5.2 Electrochemical impedance analysis
Electrochemical impedance spectroscopy (EIS) is one of the versatile electrochemical
techniques for characterizing electrochemical properties of the materials, and their interfaces in
different electrochemical environments. It is defined as the impedance of an electrode-electrolyte
interface as a function of frequency of the applied alternating current [95]. Today, it is widely used
to analyze the complex material properties such as dielectric properties, mass transport, defect
density, passive film stability, coating degradation, microstructural and compositional effects on
the conductance of solids, and impedance study of biological membranes [96-101]. The wide
spread use of impedance technique is due to the possibility of using very small amplitude signal
without disturbing the desired properties of materials to be measured. Moreover, the tests are non
destructive and provide a rapid and convenient way of characterizing physico-chemical properties.
However, the primary problem associated with EIS technique is the ambiguity associated with
data interpretation i.e. what equivalent circuit model [102] should be used out of several
possibilities. Even when, the equivalent circuit model is known, component values may not able to
be resolved properly. Nevertheless, the added dimension of frequency can provide essential
mechanistic information which would be otherwise unavailable from complimentary
electrochemical techniques [103]. Out of several applications, EIS is largely used in the field of