A Live Demonstration "A Tafel Experiment - Calculating Tafel Constants" presented on August 20th, 2020 hosted by Gamry Instruments and presented by Andrew McCaskill.
Hi thank you for the video. I actually did measurements with and without inhibitor. And with inhibitor the corrosion rate gets smaller an my anodic slope gets steeper. But all of my tafel constants (ba= 50 mV/dec; bc= 470 mV/dec) stay more or less the same because it's the only way to get a fit where the linear part of cathodic and anodic branch intersect with Ecorr. So my question is what does it mean, when the anodic branch changes and what physical meaning does the tafel constants have? Thanks
There is not a simple or straight forward answer to this question. There are many variables that can cause the tafel constants and the anodic slope to shift. When the slope of the anodic portion changes, we can say that the kinetics of the M -> (M+) + e- half reaction has changed. The cause of this is varied, and system dependent. If you email your data files to techsupport@gamry.com, we can perhaps provide more specific details, or provide resources on the topic.
Hi, I am currently doing potentiodynamic polarization corrosion testing for my research. Sorry for asking, how do we obtain the passive region in potentiodynamic polarization as shown in 17:56. Do we increase the potential applied to get the extension curve in the anodic curve?
Hello. The passive region is an inherent property to certain materials. How and where it will occur differs for each material type. Unfortunately, there is not a quick or direct answer to your question. If you have data you need help analyzing, please email it to techsupport@gamry.com and one of our engineering staff would be happy to assist.
Hi @Gamry Instruments, I am currently evaluating susceptibility of material to corrosion from Tafel plot. I'd like to ask what is the most appropriate range of current values used to evaluation by your Tafel Fit routine. Evaluation will be done by more people so I am looking for an objective way to do the evaluation. Is there any standard (ISO, ASTM,...) for this purpose? Thanks.
Due to the wide variety of materials and electrolytes used, there is no generic standard or "rule" to follow when selecting a region. The region selected should encompass the linear Tafel region, but there are no guidelines beyond this. If you commonly test the same materials and have a large data set, you can likely define a range of values more specific to your system. If you email your data set(s) to techsupport@gamry.com, one of our Technical Support Engineers can provide feedback on the selected region.
From the Tafel information can you give a time that the corrosion began? In theory you should be able to. Do you have a video on that or does Gamry have a tutorial on such a thing.
Hello. Thank you for the video. Can we make a Tafel fit combining two polarization curves? One for cathodic, and another for anodic potentials. Thank you for the answer in advance.
Yes, you are able to do this in our Analyst software. You can overlay the two files, one for the anodic and one for the cathodic. To calculate the constants you can perform an "E log I" fit, which is a Tafel fit performed on either the anodic or cathodic half of the curve. If you need any assistance performing this, please reach out to our Technical Support Engineering team at techsupport@gamry.com. We are happy to help.
@@gamryinstruments Thank you for the answer. One more question: Is it possible to correct my data (current or impedance) with surface area of the sample?
@@dmitrykurchavov9744 Yes, this is possible. Once you open a data file, you can go to Options. In here you will see a section for "Units for Current". You can select between Current (non-normalized) and Current Density (area normalized). Same applies for impedance data. If you need any assistance, please do not hesitate to reach out to our Technical Support team. www.gamry.com/contact-us/speak-to-an-electrochemist-2/
Energy density is usually determined in a cyclic charge-discharge experiment. There is a beginner guide here explaining how to setup such a test: www.gamry.com/support/technical-support/getting-started-with-gamry-software/your-first-experiment-cyclic-charge-discharge/ Electrical conductivity is usually determined via an EIS experiment. If you contact our technical support engineers at techsupport@gamry.com, they can provide specific details to make these measurements on your exact cell type. They will be happy to help!
Once Icorr, Ba, and Bc have been calculated by Tafel analysis, Faraday's law can be used to relate current to mass (and mass loss). The mass loss can then be converted to a corrosion rate. We offer a application note that shows the details of this calculation: www.gamry.com/application-notes/corrosion-coatings/basics-of-electrochemical-corrosion-measurements/
Increasing the "Init. Delay" parameter time will help ensure your sample is stable before the Tafel test begins. This can help reduce the difference between Ecorr and Eoc. If you email your data file to techsupport@gamry.com, one of our engineers may be able to provide additional suggestions
@@gamryinstrumentsOk, thank you sir I will see to that and sir one more thing, whenever this comment shows up, does this mean that the graph obtained is wrong ?
Dear sir, we know that Tafel extrapolation is only valid for high value of overvoltage : typically |80 | mV/Ecor. but here you have used potential values less than the 80 mV recommended. Can you explain.
This presentation was designed as a general overview of Tafel experimentation and analysis. In order to keep the length of the talk reasonable we did not examine the finer details, caveats, and all use cases. If you have specific questions about your Tafel data, please email techsupport@gamry.com
