Figure 6
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 4 power Ohm squared centimeters)” ranging from approximately negative 2 to 16 with an interval of about 2, and the vertical axis labeled “negative Z i (10 to the 4 power Ohm squared centimeters)” ranging from approximately negative 2 to 16 with an interval of about 2. Distinct symbols in the legend represent experimental data for each composition: 5 percent (right-pointing triangles), 10 percent (circles), 15 percent (left-pointing triangles), and 20 percent (stars). Solid lines labeled “Fitted curves” overlay each dataset. All curves form rising, depressed semicircular impedance arcs. The 5 percent sample exhibits the largest arc, extending to Z r near about 13 and peaking at negative Z i around 14. The 10 percent sample shows slightly smaller values, reaching Z r near 11–12 with peak negative Z i near 12. The 15 percent sample reaches Z r around 10 with peak negative Z i near 10. The 20 percent sample displays the smallest arc, with Z r below about 9 and peak negative Z i near 8.5. Overall, the impedance magnitude decreases progressively from 5 percent to 20 percent. Panel (b) shows polarization curves plotted as “log i (A per centimeter square)” on the vertical axis ranging from approximately negative 9 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 0.0 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 sharp V-shaped minimum near E equals approximately negative 0.26-0.28, characteristic of corrosion polarization behavior. The 5 percent curve reaches the lowest current density at the minimum (around log i equals negative 8.8 to negative 9), while the 20 percent curve generally shows higher current densities on both anodic and cathodic branches. Toward more positive potentials, the 10 percent and 15 percent curves rise more steeply, whereas the 20 percent curve remains comparatively flatter. Note: All numerical data values are approximated.Electrochemical impedance spectra (a) and potentiodynamic polarisation curves (b) of Q235 steel at 298 K in alkaline cleaning agents containing different concentrations (5%, 10%, 15%, 20%). Source(s): Authors’ own work