dear Wan Mohamad Ikhmal ;

In my opinion, you can try 20 mv s-1 without initial delay

Dear Wan

That is dependent on the materials of the sample,i.e.,conductive,semiconductive, and insulator, and the aqueous solution, i.e., ionic or not,inhibited or not,. The standard immersion time of a metallic alloy is one hour in order to monitor the open circuit potential (OCP)of the sample in the solution. After attaining a steady state OCP,one can start the test with a low scanning potential rate i.e.,5-10 mV/s, for instance for both the solution that has relatively a low value of resistivity and the sample that is relatively a conductor.Otherwise,one can use a higher scanning potential rate ,i.e.>10mV/s for hight resistive solution,inhibited, and high resistance sample,i.e.,coated sample,passive sample with oxide film on the sample ,and so on.

Dear Dr. Wan Mohamad Ikhmal ,

in addition to what Dr. Khaled J. Habib correctly said, I suggest you to have a look at the following, interstig book:

- RECENT RESEARCHES IN CORROSION EVALUATION AND PROTECTION

Edited by Reza Shoja Razavi

Published by InTech (2011) - ISBN 978-953-307-920-2

Available at: https://cicorr.uacam.mx/view/download?file=96/adjuntos/Dzib_CapLib_6.pdf&tipo=paginas

Enjoy readings and my best regards, Pierluigi Traverso.

Thank you so much for the answers dear Dr. Mahmood H. M. , Dr. Pierluigi Traverso and Dr. Khaled J. Habib

Dear Dr. Wan Mohamad Ikhmal ,

It looks like you are using Gamry software. For Gamry, the initial delay refers to how long the instrument waits prior to measuring the final OCP before starting your experiment (i.e. potentiodynamic polarization for Tafel determination or EIS).

The "stab. (mV/s)" setting is an exception to the initial delay that tells the software to start your experiment than your preset initial delay if the OCP stabilizes to your preset value. For example, if your initial delay is 600 seconds and your stabilization is 0.1 mV/s, then your initial delay may be up to a maximum of 600 seconds (for example, if stabilization occurs after 10 seconds, then the experiment starts after 10 seconds). The software uses the OCP measured at the end of your delay (i.e. 600 seconds or less if stabilization better than 0.1 mV/s occurs) in any case where you set a potential that is with respect to OCP (i.e. "vs Eoc" as labelled in the software). A stabilization of 0 means the software waits for the full "initial delay" time to pass prior to starting the experiment.

See the Gamry website for more details on this:

https://www.gamry.com/support/technical-support/getting-started-with-gamry-software/how-to-run-your-first-experiment/

and

https://www.gamry.com/assets/Uploads/Getting-Started-with-Your-First-Experiment-EIS300-PotenStatic-EIS-r1.pdf?utm_medium=email&utm_source=sharpspring&sslid=MzM2MjG1MDQ0sDS3BAA&sseid=M7Q0NDU1tzA2NwQA&jobid=382bc7db-17b7-45b2-9847-23b5abcab1b6

Also, it is important to note that the "stab. (mV/s)" setting is not the "scan rate" of the experiment (although they have the same units).

Specifically in your case, since your sample has already been immersed for a few days (and I assume ready to be tested), I would expect that the initial delay does not need to be too long since your sample has likely already stabilized. I agree with Dr. Khaled J. Habib and Dr. Pierluigi Traverso that the immersion time prior to running an electrochemical test is dependent on your specific case and what you are interested in.

With regards to the stabilization rate, for many corrosion studies you often want to be consistent with the time of immersion prior to testing so I would recommend setting the stabilization to 0 mV/s; this ensures that the full time you set for the initial delay is waited prior to testing (as mentioned in the links I provided on the Gamry website).

Good luck in your testing!

Cheers,

Leo

Some of the answers refer to scanning rates, but that isnot the point here.

As metioned by Leo Monaco, the initial delay may be set as time or drift rate (stabilization).

Depending on the system (material and testing environment), the time needed for stability may vary. As an example, if we are testing a paint specimen for different times of immersion and you are performing an EIS test after 3 or 4 days, its potential will be already steady and the initial delay may be of 5 min. On the contrary, if you immerse a Ti specimen in a saline solution, the evolution of its passive layer up to a steady state may take more than 24 h.

So, the definition of the initial delay should depend on the previous experience with the system being studied.

Dear Dr. Leo Monaco and Dr. J.C.S. Fernandes , thank you so much for the clarification !!

Check https://www.researchgate.net/topic/Electrochemical-Impedance-Spectroscopy

https://www.gamry.com/application-notes/EIS/basics-of-electrochemical-impedance-spectroscopy/

Also check https://www.sciencedirect.com/science/article/pii/S0013468618322345

https://www.sciencedirect.com/science/article/pii/S0013468615006325

Some have 30 minutes as shown in this paper

Article Reducing subjectivity in EIS interpretation of corrosion and...

The suitable duration for the initial delay in EIS measurement for corrosion study depends on the type of corrosion and the environment in which the sample is being tested. In general, a delay of 10 to 30 minutes is sufficient to allow the sample to reach a steady state. However, for some types of corrosion, a longer delay may be required. For example, if the sample is being tested for pitting corrosion, a delay of 1 to 2 hours may be required.

Here are some factors to consider when determining the suitable duration for the initial delay:

• Type of corrosion: The type of corrosion will affect the rate at which the sample reaches a steady state. For example, pitting corrosion is a more aggressive type of corrosion than uniform corrosion, and it will require a longer delay to reach a steady state.
• Environment: The environment in which the sample is being tested will also affect the rate at which it reaches a steady state. For example, a sample that is being tested in an aerated solution will reach a steady state more quickly than a sample that is being tested in an anaerobic solution.
• Sample size: The size of the sample will also affect the rate at which it reaches a steady state. Larger samples will reach a steady state more slowly than smaller samples.

It is important to note that the initial delay is not always necessary. In some cases, it may be possible to start the EIS measurement immediately. However, in general, it is advisable to wait for a short period of time to allow the sample to reach a steady state. This will ensure that the EIS measurements are accurate and that the results are reliable.

Here are some additional tips for conducting EIS measurements for corrosion study:

• Use a controlled environment. The environment in which the sample is being tested should be as controlled as possible. This will help to ensure that the results of the EIS measurements are accurate.
• Use a reference electrode. A reference electrode is used to measure the potential of the sample. This is important because the potential of the sample can affect the results of the EIS measurements.
• Use a sweep rate that is appropriate for the system. The sweep rate is the rate at which the frequency of the EIS measurement is changed. It is important to use a sweep rate that is appropriate for the system being studied.
• Use a data acquisition system that is capable of storing a large amount of data. EIS measurements can generate a large amount of data. It is important to use a data acquisition system that is capable of storing all of the data.
• Analyze the data using appropriate software. There are a number of software packages that can be used to analyze EIS data. It is important to use software that is appropriate for the type of corrosion being studied.

By following these tips, you can improve the accuracy and reliability of your EIS measurements for corrosion study.