Figure 4
The figure contains two side-by-side plots labeled (a) and (b), comparing electrochemical behavior for four compositions: 5 percent, 10 percent, 15 percent, and 20 percent. Panel (a) presents Nyquist plots with the horizontal axis labeled “Z r (10 to the power 4 Ohm squared centimeters)” ranging from 0 to 8 with an interval of 1, and the vertical axis labeled “negative Z i (10 to the power 4 Ohm squared centimeters)” ranging from 0 to 8 with an interval of 1. Distinct symbols in the legend represent experimental data for each composition: 5 percent (right-pointing triangles in magenta), 10 percent (green circles), 15 percent (left-pointing triangles in pink), and 20 percent (blue stars). Black solid lines labeled “Fitted curves” overlay each dataset. All curves form rising, depressed semicircular impedance arcs. The 10 percent sample shows the largest arc, reaching Z r values near 6.5 and negative Z i near about 4.5. The 5 percent and 15 percent samples show intermediate responses, with peak negative Z i around 3 to 3.8. The 20 percent sample exhibits the smallest arc, with Z r below about 4 and peak negative Z i around 1.5. Overall, the impedance magnitude decreases from 10 percent to 20 percent, with 20 percent showing the lowest values. Panel (b) shows polarization curves plotted as “log i (A per centimeter square)” on the vertical axis ranging from negative 10 to negative 4 with an interval of 1 versus “E (V per S C E)” on the horizontal axis ranging from approximately negative 0.5 to 0.1 with an interval of about 0.1. Four colored curves correspond to the same compositions: 5 percent (magenta), 10 percent (green), 15 percent (pink), and 20 percent (blue). Each curve displays a pronounced V-shaped minimum near E equals approximately negative 0.26, characteristic of corrosion polarization behavior. The 10 percent curve reaches the lowest current density at the minimum (around log i equals negative 9.4), while the 20 percent curve shows the highest current densities on both anodic and cathodic branches. Toward both more negative and more positive potentials, all curves rise smoothly, with separation between compositions becoming more evident at higher potentials. Note: All numerical data values are approximated.Electrochemical impedance spectra (a) and potentiodynamic polarisation curves (b) of Q235 steel at 298 K in neutral cleaning agents containing different concentrations (5%, 10%, 15%, 20%). Source(s): Authors’ own work