I want to obtain the bode and Nquest plot for PEO coated AZ91 magnesium alloy. I tried for various frequencies ranges with 10mV AC input. sometime the experiment runs and some time it gives error. When the experiment run it give me incomplete loop and than completely zig zig loop. Usually for short time as 7min, the experiment runs however when i increase the time by increasing the frequency range the experiment gives again errors. please let me know what are the possible mistake i am doing due to which i am facing these errors.?
For electrochemical impedance, frequencies higher than 100 kHz may be complicated, as you will have effects from cabling etc. Now, if you want to have information on the onset of eventual corrosion processes, frequencies lower than 1 Hz are advisable, in principle down to 10 mHz.
The initial impedance of the system, if the coating is very protective, may be very high, and this could explain your errors. Some impedance equipments are not supposed to work well at very high impedances (higher than 10-100 Mohm) and that may be the reason for your problems. Which equipment are you using?
Hello,
With immersion time the system becomes more stable and the reproducibility of the EIS data appears to be improved. We have observed significant deviations in the impedance diagrams immediately after immersion that decrease quickly and strongly with immersion time .
Have a nice day
@Quentin meyer , my voltage is AC.
@S.Feliu Jr we have waited for more than 3 hours to start the experiments.
Dear Zee:
Hello¿
Thank you for your answer
During the first hours or first day of exposure,,some authors have observed significant variations in the values of impedance measured under similar conditions attributed to the statistical nature of the initial corrosion process (pitting, filaments....).
During the later stages (more than 1day), the variations decrease quickly and strongly with immersion time indicating a homogeneous corrosion layer formation,
Have a nice day
@S. Feliu . today i started the process again for the sample which was remained in NaCl solution for a week . the sample is PEO coated AZ91. the now EIs experiment is only for 1 hr. and it showing significant variation in the impedance with frequency. However, i hop it will be stabilized with time as per your suggestion that it get stabilized with time.
@JCS Fern... I ma using Biologic-science instrument. I now successfully obtained the plot however can you suggest any proper software to fit the data.
Dear Zee
I am used with ZView from Scribner. Up to now, I think it is the most user-friendly fitting software.
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