If I have a Nyquist graphs, is it possible to see the difference without make fitting? I mean which will be more corroded over than others.
Thanks
I corrosion process is an active process on the surface. Current flows easily, this means the resistance of your system is low compare when no corrosion process or a passive layer. EIS monitors the metal-electrolyte interface, if you are comparing the same system maybe you can estimate, but changing the electrolyte and metals is hard to say because the kinetics might change.
In my opinion, the corrosion studies by EIS are best interpreted from Bode plots.
Nyquist plot will give the best comparison with variation in the resistance at lower frequency region i.e final resistance value.. when u have to take the real value of Z at lower frequency u can compare the systems.. At the same time based on the experiment condition and your sample the arc some time not in trend but even though it could give the idea about one system with respect to other.. but u have to take Modulus of Z value from Bode plot also will give idea...
If I have a Nyquist graphs, is it possible to see the difference without make fitting? I mean which will be more corroded over than others. The Nyquist plots give an idea, which is the best material.
Nyquist and Bode Plots gives complementary information about the system you are studying, see in lower frequency IZI or phi angulus or in the Nyquist, the CTR charge transference resistant.
You must analize Bode fi vs frequency and Bode I Z I vs frequency and Nyquist at lower frequencies, then Polarization Curves (corrosión currents) and Microscope studies to compare different system and define wich is the best material. Dr. Zulema Ángela Mahmud
Theoretically, for a corroding system under kinetic control the Nyquist plot shows a semi circle capacitive loop whose diameter is directly proportional to the corrosion resistance of the sample. So, one can compare the behavior of two samples in same medium or the effect of any tested parameter on the behavior of a system by comparing the length of this diameter without make fitting. Herewith I attach a helpful pdf for your consideration.
in our studies about the corrosion of magnesium alloys we normally associate the diameter of the capacitive loop in the high frequency region with the charge transfer resistance (RCT) of the corrosion process, value which is inversely related to the corrosion current (icorr) through the well known Stern-Geary equation:
icorr= B/Rct:
B being a proportionality constant which depends on the Tafel slopes, βa and βc.
For example in:
https://www.researchgate.net/publication/280007891_Corrosion_product_layers_on_magnesium_alloys_AZ31_and_AZ61_Surface_chemistry_and_protective_ability
Article Corrosion product layers on magnesium alloys AZ31 and AZ61: ...
dear Felix
is high frequency loop has to do with corrosion?
see the time scales
only at low frequency range corrosion occurs and not at high frequencies
Dear prof V.S Muralidharan ·
Thank you for your answer. Please see Figure 5 of the attached manuscript in which we compare the corrosion rate obtained from the EIS measurements by using the diameter of the capacitive loop in the high frequency region with the values obtained by two independent techniques (gravimetry and hydrogen evolution). They are consistent.
Kind regards.
Dear Feliu,
In your comment , something should be corrected as follows:
.... of the capacitive loop in the low frequency region ... This is because the charge transfer resistance (Rct) will dominate the ac respose of the redox system at the low frequency region. Thank you.
Dear Dr. Fakiha,
Thank you for your interesting comment. In our studies, we tipically obtain the capacacitative arc whose diameter is used for the corrosion rate estimations in a frequencies range from 100 kHz to 1 Hz.
Kind Regards
PLEASE ATTEMPT TO FIT EQUIVALENT CIRCUIT YOUR SYDTRM IS NOT EASY ONE TP MODEL
Your system is an alloy covered by an oxide film in a highly condutive solution
Two RC circuits
Now simultaneously do log z vs log plot. ..
And theta vs log f analysis
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