CHEM02200704003 Nilamadhab Pandhy - Homi Bhabha National ...

Chapter 3
All the measurements were carried out in open circuit potential condition in standard
electrochemical cell as mentioned earlier consisting of specimen as working electrode, Ag/AgCl
as reference electrode, and platinised platinum as counter electrode using Solatron 1255
Frequency Response Analyzer associated with 1287 electrochemical interface. The experiments
were carried out in the frequency range from 10 -1 Hz to 10 5 Hz by superimposing an AC voltage
of 10 mV amplitude with data density of 5 points per decade.
3.1.5.3 Potentiodynamic polarization study
Potentiodynamic polarization is probably the most commonly used polarization technique
often used for testing corrosion susceptibility. This technique can provide significant information
regarding corrosion mechanism, corrosion rate, and corrosion of specific materials in designated
environments. A polarization curve can provide evidences whether or not a material is active,
passive or active-passive. Apart from this, passivity and corrosivity can be determined in presence
of oxidizing-reducing species also. One of the major advantages of potentiodynamic polarization
study is quick determination of corrosion rate as compared to traditional weight loss methods. In
this technique the corrosion rate is determined by extrapolating linear segments of cathodic and
anodic regions (Tafel lines) [104]. The intersection of the Tafel lines gives the corrosion potential
and corrosion current density.
Potentiodynamic polarization method involves changing the potential of the working
electrode at a fixed rate, and monitoring the current density which is produced as a function of
potential [93]. The instrumentation for carrying out the polarization study consist of a potentiostat
which maintains the potential of the working electrode according to the preset value. A current
measuring device (electrometer) for measuring the current produced by the applied potential.
Polarization cells for carrying out polarization study consists of, (a)
working electrode i.e.
specimen to be tested, (b) a non-polarizable counter electrode for completing the circuit, and (c)