Greetings,
I just read an article which says that for the analysis of corrosion using EIS, a low frequency limit should be chosen to ensure minimal change in system during data collection.
My question is quite simple, since the max limit of EIS is 1 MHz, then what is this range of low frequency limit I should be choosing?
Dear Dr. Wan Mohamad Ikhmal,
I have often used an EIS set up that gives me good results in the evaluation of protective protection of organic coating systems for the automotive sector.
In setting impedance measures, several instrumental parameters were defined, such as the potential amplitude ranging around the balance potential and able to generate superimposed alternate current (+10 mV) and the frequency range (gradually dropping from 65 kHz to 100 mHZ). With these settings, the average measurement took about twenty minutes. Lower frequencies would have taken more time and it would have been more difficult to keep a stationary system condition. In other words, if it takes too much to measure, it will not just be impractical hence difficult to apply in industrial settings, but the measurement will also significantly depend on the system evolution. Many times, when we have a coating with a high protection power, an exclusively capacitive behavior is observed with a very high system impedance at low frequencies. No stable potential can be measured owing to strong fluctuations caused by electric insulation between the working electrode and the reference electrode. Impedance was measured on specimens that had been submerged in the solution for periods from 2 to 240 hours (on the same specimens, since this is not a destructive test) in order to monitor the system evolution over time.
Best regards, Pierluigi Traverso
Dear Wan Mohamad Ikhmal ,
If the object of your research are organic coatings, the lower frequency range is less important because the system during the measurement is rather stable. In the case of "pure" electrochemistry and corrosion you need to observe impedance spectra at low frequencies because due to the dynamics of changes in the system there may be behavior difficult to unambiguously interpret. The frequency range depends primarily on the system being tested. For example, if we want to study the adsorption processes of low frequency inhibitors, we need them. The solution is also the use of a package of sinusoid.
thank you very much especially to Dr. Pierluigi Traverso , Dr. Benbouzid Abdelmoheiman Zakaria
and Dr. Stefan Krakowiak for the answers. It really helps me a lot !!
Dear Wan
In general, the frequency range of EIS analysis is between a maximum value of 1MHz to a minumum value of 0.01Hz.
However, as far as the frequency range of the minimum value, the minimum frequency range should include the 0.16Hz frequency value. Because at a such value, the angular velocity w=2Pf=1 (where P =3.14and f is the frequency). So on the abscissa coordinate (X-axis) of Bode plot at log{w}=log{2(3.14)x(0.16)} =log{1}=0. So at f=0.16 Hz, a tested sample by EIS would be at its open circuit potential in an aqueous solution. As a result, one can determine the polarization resistance of the sample , which corresponds to the open circuit potential of the sample in the solution. Subsequently, from the polarization esistance , one can determine the corrosion rate from Stern and gary equation.
Refer to the attachment for how to do the above procedures:
Generally, in corrosion studies, the most commonly choosen range is 100KHz to 10mHZ. Good luck
hi..can i ask suggestion jurnal that have frequency and amplitude data from eis measurement for analyses corrosion rate of mild steel coating
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