Please have a look at this figure, does it ever reflect that an EIS measurement has been made at t=5000 s and at t=10,000 s?
Thank you Adel for the notes, the Nyquist plots are not ready yet actually. You can see the abrupt change in the OCP vs. time after holding the OCPs for nearly 300 s during an EIS test from 10 kHZ to 0.01 Hz at 4000 and 9000 s. That what made me think of the reliability of the readings. Thank you again.
Here is the Nyquist plots. The EIS measurements were made after 5000, 10000 s and at the end of the OCP monitoring, at 15000 s
The WE tested is a high-strength steel immersed in a low-pH CO2-saturated solution of 10 g/L chloride. This Nyquist plot is typical for similar CO2-saturated systems. The plot seems composed of two depressed semi-circles overlapped at low frequencies. They reflect the continuous dissolution of the substrate and the simultaneous build-up of the corrosion products that raise the charge-transfer resistance over time. You can see the continuous increase in the size of the Nyquist profiles. If you have any comments please share.
Hi Adel,
I am using actually a range of chloride concentrations to study their effects on the corrosion behavior. The chloride concentrations in the pipeline flows are on a large scale of variation. Also, the chloride concentration in a pipeline flow is subject to change in association to many environmental factors if the flow is of a high water content. Yes, I have bode phase plots, but I depend on them for longer periods of immersion and in mildly-alkaline (bicarbonate) solutions - for which I conducted weight loss measurements.
Thank you Binod for your input.
Hi Faysal....
Whether yo can study lower or longer immersion periods, Bode plots gives realistic picture of your system. If your Nyquist plots exhibit two loops in semicircle, you will also get two phase angle maxima in your Bode plots. In your environment you can immerse the sample for 30 min or 1 h before the experiment. During this time OCP will be stabilized, later you can proceed with your experiment. In our case we have been tested our samples for a maximum immersion period of 90 days. In your case the Rct value is increasing with immersion time, because, there is formation of metal oxide on the metal surface. This metal oxide will protects it from corrosion up to some extent. So my sincere advice is increase your immersion time, until the Rct values are decreased.
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