Rencently, i found the corrosion rate calculated from the ''tafel plot'' is very different from the one which from the ''weight loss test'', cound anyone tell me which method is better to calculate the corrosion rate???
In addition, the corrosion rate calculated automatically form the commercial software in electrochemical workstation is accurate??? Which equation does the software use?? is it Stern-Geary's equation???
Both methods provide a measurement of corrosion rate, but they are measurements of different things. The electrochemical measurement that you made provided an instantaneous measurement of the corrosion rate at that specific time. The measurement makes a couple of assumptions to be discussed later, but generally provides a fair representation of what is happening on the metal surface in your test at the time that you make the measurement.
Weight loss measurements integrate the multitude of instantaneous corrosion rates that occurred during the test. A weight loss measurement will generally provide an accurate measurement of this integrated corrosion rate over the exposure time period. Often, the corrosion rate will start at a very high rate and will decrease over time. This can be caused by a buildup of corrosion products in the test solution or on the metal surface or changes in the metal surface that occur as the initial layer is removed.
As for the commercial software, either for computers or built into corrosion instruments, assumes values for the anodic and cathodic tafel constants. Normally the difference between the assumed values and the actual ones is not enough to introduce much error into the measurement. However, occasionally the chemistry of the corrosion reaction results in tafel constants deviate from the assumed values. In these cases, a "measured" corrosion rate using the assumed values and the real corrosion rate can differ enough to be important. Fortunately, most of the software have procedures that allow you to adjust the tafel constants if you have better information.
Both methods provide a measurement of corrosion rate, but they are measurements of different things. The electrochemical measurement that you made provided an instantaneous measurement of the corrosion rate at that specific time. The measurement makes a couple of assumptions to be discussed later, but generally provides a fair representation of what is happening on the metal surface in your test at the time that you make the measurement.
Weight loss measurements integrate the multitude of instantaneous corrosion rates that occurred during the test. A weight loss measurement will generally provide an accurate measurement of this integrated corrosion rate over the exposure time period. Often, the corrosion rate will start at a very high rate and will decrease over time. This can be caused by a buildup of corrosion products in the test solution or on the metal surface or changes in the metal surface that occur as the initial layer is removed.
As for the commercial software, either for computers or built into corrosion instruments, assumes values for the anodic and cathodic tafel constants. Normally the difference between the assumed values and the actual ones is not enough to introduce much error into the measurement. However, occasionally the chemistry of the corrosion reaction results in tafel constants deviate from the assumed values. In these cases, a "measured" corrosion rate using the assumed values and the real corrosion rate can differ enough to be important. Fortunately, most of the software have procedures that allow you to adjust the tafel constants if you have better information.
Hello,
Good Day!
Perhaps you may finf interesting the attached paper which aims to elucidate the main benefits and limitations from simple mass loss experiments to more complex electrochemical methodd in the case of the biodegradation behaviour of Mg and its alloys.
https://www.researchgate.net/publication/51846498_Assessing_the_corrosion_of_biodegradable_magnesium_implants_A_critical_review_of_current_methodologies_and_their_limitations
Have a nice day
Kind regards
Article Assessing the corrosion of biodegradable magnesium implants:...
Hi Pengpeng
You asked to know which method is better to calculate the corrosion rate. I think Prof Stephen addressed part of the story.
In my opinion, following the international standards for each technique is the only way to get satisfied results. For example, use ASTM G-102 and related standard practices for calculation of corrosion rates and related information from electrochemical measurements, and for weight loss method use ASTM G-1 as standard practice for preparing, cleaning, and evaluating corrosion test specimens. I recommend for you to stand on one standard practice to standardized your test and calculation procedure. This trend will narrow the difference in the results.
Thanks
Corrosion rate obtained by tafel method or another electrochemical methods is momentary corrosion rate and obtained by weight loss measurements is total corrosion rate. Both value must be different.
Hello,
Good Day!
Perhaps you may find interesting the attached paper:
https://www.researchgate.net/publication/231375757_Bridging_Gravimetric_and_Electrochemical_Approaches_To_Determine_the_Corrosion_Rate_of_Metals_and_Metal_Alloys_in_Cooling_Systems_Bench_Scale_Evaluation_Method
Have a nice day
Kind regards
Article Bridging Gravimetric and Electrochemical Approaches To Deter...
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