Figure 2
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 (Ohm squared centimeters)” ranging from negative 100 to 400 with an interval of 50 and the vertical axis labeled “negative Z i (Ohm squared centimeters)” ranging from negative 100 to 400 with an interval of 50. Distinct symbols at 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 depressed semicircular arcs typical of impedance spectra. The 5 percent sample shows the largest semicircle, extending furthest to the right (Z r near 350) and the highest negative Z i values (around 140). The 10 percent and 15 percent samples display intermediate arc sizes, while the 20 percent sample exhibits the smallest semicircle, centered around Z r values near 150–200 with peak negative Z i near roughly 70–80. The trend indicates decreasing impedance arc diameter with increasing percentage 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 negative 8 to negative 3 with an interval of 1 versus “E (V per S C E)” on the horizontal axis ranging from negative 0.9 to negative 0.3 with an interval of 0.1. Four lines correspond to the same compositions: 5 percent, 10 percent, 15 percent, and 20 percent. Each curve exhibits a sharp minimum near E equals negative 0.55, forming a V-shaped profile characteristic of corrosion polarization behavior. The 15 percent curve reaches the lowest current density at the minimum (around log i equals 8), while the other compositions show slightly higher minima. Toward both more negative and more positive potentials, all curves rise smoothly, with the 20 percent sample generally exhibiting higher current densities than the others over much of the potential range. Note: All the numerical data values are approximated.Electrochemical impedance spectra (a) and potentiodynamic polarisation curves (b) of Q235 steel in acidic cleaning agents containing different concentrations (5%, 10%, 15%, 20%) at 298 K. Source(s): Authors’ own work