Dear Sir. Concerning your issue about the using potentiostat/ galvenostat of the company "CorrTest". I think the following below links may help you in your analysis:

http://www.corrtest.com.cn/uploads/soft/170904/CS350potentiostat-Corrtest.pdf

http://www.corrtest.com.cn/uploads/soft/160616/InstallationguidanceofCSPotentiostat.pdf

http://www.corrtest.com.cn/uploads/soft/170828/manual.pdf

Thanks

Dear Dr. Saeed sb,

A1: I am not using this potentiostat but i can answer your questions

A2: (i)The OCP stabilization before corrosion testing is very important. For this the potential stability is more important than fixing the time for OCP. You may start polarization test once you achieved stability of approximately 1mV/sec in the OCP. The large variation could affect the polarization behavior and reproducibility in the results.

ii. You can only get the potential (OCP) profile by connecting with potentiostat and the large impedance (in the internal circuit of potentiostat) would restrict the current flow between working and counter electrode (open circuit mode).

iii. You will get potential vs. time plot (OCP) of the sample and need to meet stability criteria.

iv. once you immerse the sample (WE) in solution, the WE will tend to establish equilibrium with the electrolyte (Indicated as OCP), run OCP until you get the stability. Then you will go for Tefel plots. You may select -250mV and +250mV (vs. OCP) as initial and final potentials, respectively. You may select 0.1 or 0.1666 mV/sec scan rate. You may also select higher scan rate but this depends on the reactivity of the metal under study in the respective electrolyte. The very high scan rate may include diffusion controlled processes which may add up in the polarization trend. In this way the activation controlled processes (used to calculate corrosion rate and other kinetic parameters) will under/over estimated.

v. You will get E vs. log i plot (Tafel plots), The linear potions (in both cathodic and anodic branch but 50-100mV away from the Ecorr) are extrapolated to get the icorr and Ecorr values. The slopes of these linear trends depict the Tafel slopes.

vi. Inhibitors are categorized based on their tendency to restrict anodic or cathodic reaction. The mixed affect both anodic and cathodic electrochemical behavior. Simply if you get higher polarization (larger anodic Tafel slope) in the anodic trend in the presence of inhibitor than without inhibitor, this species will control the anodic process and vice versa.

I hope i answered your questions and if you have further queries, you may also reach me via my official email.

regards

K. M. Deen

+1 Kashif's answer which is excellent. I just wanted to add that the Tafel plot and understanding are based on Butler-Volmer and assume that only one species is undergoing oxidation and one reduction. This assumption is not necessarily valid for all systems but it can still be used for quantitative evaluation of inhibitor performance (for example).