what's the difference of running cathodic or Anodic potentiodynamic sweep separately or running the potentiodynamic including cathodic and anodic together at the same time ( example -5mv to 5 mv )?
my experience for the past 35 years in CV- i called this 1980 as TPSV triangular potential sweep voltammetry as the input is isosceles triangle
start with a clean surface that is the potential in which copious evolution of hydrogen
go anodic - net cathodic current will decrease - there will be a potential i named as ZCCP
that is zero current crossing potential in which the net anodic current= net caothoridc current = corrosion current
then proceed further you will have anodic currents flowing
For corrosion current density measurements start from -300 mV cathodic to OCP or steady corrosion potential --go anodic you will cross OCP and go anodic upto +300 mV
then do analysis
Qusay,
Every zone will give you information about the processes that occur on the surface of your material. Please refer to the Mix-potential theory in a corrosion book. Also you can read about Tafel slopes.
https://books.google.com/books?id=Zl2XlEOuJnMC&q=corrosion+engineering&dq=corrosion+engineering&hl=en&sa=X&ved=0CDAQ6AEwAGoVChMI_pTOx_zpxgIVRIMNCh2VzwDK
https://books.google.com/books?id=YILALB8g3c0C&dq=corrosion+engineering&hl=en&sa=X&ved=0CE0Q6AEwBWoVChMI_pTOx_zpxgIVRIMNCh2VzwDK
https://books.google.com/books?id=D0nAMorpSIYC&dq=corrosion%20engineering&source=gbs_similarbooks
Thanks a lot Enrique Maya , I have one of these books and I'll try to get the first one , but What I mean that some people run anodic or cathodic potentiodynamic separately while others run potentiodynamic for both anodic and cathodic together by using sweep range from -ve to +ve potential. what's the difference between of two methods?
the moment you polarize the surface changes
surfaces are different in both these cases results would be different
Hi,
As rightly pointed out, the concept of polarization depends on the potential applied to the surface. During cathodic polarization, the potential is much lower while during anodic polarization a much higher potential is applied. And in a polarization measurement from cathodic to anodic, the sample surface changes dramatically and the resultant electrochemical behaviour is seen in terms of the corrosion current densities. So its not only that the polarization measurements are conducted separately will the surfaces be different, it will also depend on what point the start and end potential is applied to the sample surface. So, before carrying out the electrochemical measurements carefully plan the experiment and understand the results you have achieved, before concluding the behaviour of the surface
As other respondents have noted, potentio-dynamic scans are destructive tests (i.e. they change the very surface being studied). This is why different pieces of metal are commonly used for cathodic and anodic scans. This is also why repeat measurements have little meaning, since the substrate is being changed by the test itself. Replication is accomplished by taking fresh, unexposed metal pieces and running the test of them.
Anodic scans will oxidize the surface (although in the presence of appropriate agents, passivation may occur) followed by a breaking down of that passive layer. After breakdown, oxidation typically becomes pitting in nature.
Cathodic scans reduce the surface, and may serve to clean it of various adsorbed materials. It too produces passivation, but from a different region of the Pourbaix diagram. Thus, the nature of the passivation is different, and the changes in the substrate are different from anodic scans.
Because you are dealing with a destructive test, it makes no sense to run both scans on the same sample.
Are you talking of cyclic volatammetry when referin to "running the potentiodynamic including cathodic and anodic together at the same time"?
my experience for the past 35 years in CV- i called this 1980 as TPSV triangular potential sweep voltammetry as the input is isosceles triangle
start with a clean surface that is the potential in which copious evolution of hydrogen
go anodic - net cathodic current will decrease - there will be a potential i named as ZCCP
that is zero current crossing potential in which the net anodic current= net caothoridc current = corrosion current
then proceed further you will have anodic currents flowing
For corrosion current density measurements start from -300 mV cathodic to OCP or steady corrosion potential --go anodic you will cross OCP and go anodic upto +300 mV
then do analysis
Dear Prof. V.S Muralidharan
Thanks a lot for all your explanations, they are really valuable. I am using +- 150 mV vs. OCP to minimize the change in the surface. Do you think it would be any difference if I use a wider range?
All the best
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