During calculating the corrosion parameters using tafel extrapolation method what does it mean if the values of anodic and cathodic tafel slopes are coming out same (approx.).
Dear Mehta
It depends on how much the value of the slopes are changed. You can only interpret if the values are changed significantly, otherwise the interpretation can not be accurate. Please send me your type of materials and the type of corrosive medium for further discussion.
Tafel slope is given by the relation: 2.3RT/a.n.F, where a = transfer coefficient, n = number of electrons involved in the rate controlling reaction. If you get similar Tafel slopes for anodic and cathodic reaction (nothing unusual about it), it indicates that the transfer coefficient is 0.5, and the same number of electrons are involved in both the reactions.
Dear Dr. Harshal Mehta,
from the Tafel slope you can deduce whether your rate-determining step involves an electron transfer or not, as well as the number of electrochemical (involving an electron transfer) and chemical (not involving an electron transfer) steps.
In a reaction involving only one step with one electron transfer, the Tafel slope will be of about 100 mV/dec. In a more complex reaction involving several steps and several electron transfers, the Tafel slope will be determined by the reaction kinetics and by the number and nature (i.e., involving an electron transfer or not) of the preceding steps.
If you have obtained similar values of anodic and cathodic tafel slopes you can reasonably suppose that the kinetics related to the electron transfer and the number and nature of electrons involved in the two reactions (anodic and cathodic) are also similar.
Best regards, Pierluigi Traverso
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