S65687 PRACTICAL ASSESSMENT

Creating Nyquist Plot in Excel00:00:24

The video starts by explaining how to create a Nyquist plot in Excel. It involves using the 'Insert' tab, selecting 'Chart', and choosing a 'scatter with smooth line and makers' graph type. X-values (Z real in Ohms) and Y-values (V imaginary in Ohms) for inhibitor coating and control samples are then inserted, and the axes are labeled accordingly.

Creating Tafel Plot in Excel00:01:17

The process for creating a Tafel plot is similar to the Nyquist plot. A scatter graph type is chosen, X and Y values are inserted, and axes are named. The Y-axis is labeled 'Lock IO' and the X-axis as 'Electrode potential versus e EO'.

Extrapolating Nyquist and Tafel Plots00:01:46

For the Nyquist plot, dotted lines are extended to find the polarization resistance. For the Tafel plot, two tangent lines are drawn for each curve, and a straight line is drawn to find the corrosion current (Icor) and corrosion potential (Ecor).

Comparing Polarization Resistance (RP) Values00:02:48

After extrapolation, polarization resistance (RP) values are determined for the inhibitor, control sample, and coating. The inhibitor has an RP of 5.3, the control sample 2.80, and the coating 5.40. To determine the most efficient corrosion protection, the highest RP value and the largest semicircle diameter on the Nyquist plot indicate better corrosion resistance. Based on this, the coating method is chosen as the most effective.

Comparing Corrosion Current and Potential (Icor, Ecor) Values00:03:41

The video then compares Icor and Ecor values for different time points (0 minute, 10 minutes, and smart). A lower Icor value indicates higher corrosion resistance, and a more positive Ecor value signifies a lower thermodynamic tendency for corrosion. The 0-minute measurement shows the best corrosion protection based on these criteria, followed by 10 minutes, and then smart.

Constructing the Equivalent Circuit00:05:41

Finally, an equivalent circuit is constructed based on the shape of the Nyquist plot. Since all graphs exhibit a semicircle shape, the common equivalent circuit used is R(RC), which consists of two resistors and one capacitor.