using potentiodynmic polarization experiment , if there is a difference between the corrosion resistance and corrosion rate for two sample which one will be given wieghtage and why. pleas explain!
Hi Zeeshan,
If I understood your question correctly, Corrosion rate is a kinetics term (amount of metal reacted or corroded with respect to the time), which is obtained from ICorr of the polarization curve. Whereas Corrosion resistance is a thermodynamics term and can be obtained from Ecorr of the polarization curve. Both may have a significant effect on corrosion, higher the Ecorr, more the free energy required to initiate corrosion (more stable and passive) and lower the Icorr lower the corrosion and corrosion rate.
The corrosion resistance is the the corrosion potential by which the anodic and cathodic reactions are kept in balance. Please look at the attached Fig (mark as Ecorr).
The corresponding value of Ecorr is Icorr which is the corrosion rate of the metal. You can use these two values in order to study the polarization resistance of different samples.
By plotting a linear graph for (applied potential– Ecorr) versus current, the polarization resistance can be calculated, by the slope of curve= ∆E/∆i when ∆E →0), where
∆E variation of the applied potential around the corrosion potential and
∆i is the resulting polarization current.
If you'll calculate those values for different sample you will be able to compare which one will corrode faster.
Yes, there is difference between the corrosion rate and corrosion resistance. The corrosion rate is quantitative term calculated form the value of corrosion current density adopted from the polarization plot, while the corrosion resistance is qualitative term. It used for verifying and ranking materials according to one or more than one variables adopted from the polarization plot. For example: general corrosion rate, pitting potential, corrosion potential, critical current density, and passive region width, break down potential... ect.
Best regards
Please look at my book: Magnesium 97 : proceedings of the First Israeli International Conference on Magnesium Science & Technology.
Thanks you Dr Vignesh Nallasivam and Ravit Silverstein for your vluable reply. As for as i understoood that both these paremeters portray the same feature of any metal. However, in case of genral understand and industrial applications corrosion rate is more important term to catogarize metals and brand them for the sale. The corrosion rate show more clearly what is the future of a specific metal in terms of corroison while that kinf of information can not be assumed clearly from the corrosion resistance.
I must add to the comment of @Dr Mohammed hussein can you elaborate you quantitaive expalantion a bit more.
@Ravit Silverstein what are the variables on which these both functions depends. sometimes from the tafels curves of two samples, higher corrosion rate gives high corroiosn resitance while low corrosion resistnace sample have low corroison rate. how this can be explained ?
dear Vignesh Nallasivam
"higher the Ecorr, more the free energy required to initiate corrosion"
I think Ecorr is a kinetick parameter not thermodynamic, I know the relation between reversible potential with free energy but not Ecorr with free energy ? How you relate them?
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