# _Laasonia inermis_ as an Active Corrosion Inhibitor for Mild Steel in Hydrochloric Acid
## 3 Results and Discussion
### Electrochemical Measurements  
Electrochemical measurements are useful to identify the effects of corrosion inhibitors on anodic and cathodic reactions [19] and, at the same time, monitor the progress of these reactions. Figure 3: Inhibition efficiency versus concentration of _Lawsonia inermis_ for mild steel corrosion in (**a**) 0.1 M and (**b**) 1 M HCl at 30 \({}^{\circ}\)C.  
Potentiodynamic Polarisation (Pdp) Results for Mild Steel  
The Pdp graphs for the mild steel in 0.1 M and 1.0 M HCl with or without LI at 30 \({}^{\circ}\)C are as seen in Figure 4 below. The electrochemical variables, like the corrosion potential (Ecorr) and corrosion current densities (Icorr), are presented in Table 1.  
The results depicted in Figure 4 show that there was a significant shift in (Ecorr) towards more positive (anodic) values when the LI extract was added to the 0.1 M and 1 M HCl solutions. The two arms of these curves represent the cathodic and anodic arms. The upper curve represents the corrosion behaviour of the mild steel before the addition of the inhibitor. The lower curve represents the shift in the cathodic and anodic arms with the addition of the inhibitor. This shift suggests that the electrochemical behaviour of the mild steel's surface was modified when the surface was in contact with the LI extract, thus suggesting a change in its corrosion kinetics and mechanism. This behaviour typically shows an increased tendency for the metal to resist corrosion, which is often associated with the adsorption of the inhibitor on the metal surface to block active sites for contact of the metal with the corrosive environment, thus reducing the rates of the anodic and cathodic half-reactions. In addition, the observed changes in the cathodic and anodic curves suggest the ability of the LI extract to affect multiple steps of the corrosion process. The cathodic half-reaction suggests that the reduction of the oxygen may have been slowed down with the addition of the LI plant extract, while the anodic reaction showed the suppression of the iron dissolution as a result of modifications in the surface chemistry. This indicates the ability of the LI extract to effectively alter the corrosion of metals in aggressive environments and preserve the integrity of the metal. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**System** & **Ecorr** & **Icorr** & \(\mathbf{\Theta}\) & **IE (\%)** \\ \hline
1 M HCl & \(-500.4\) & 183 & & \\
100 mg/dm\({}^{3}\) LI & \(-468.3\) & 113.5 & 0.381 & 38.1 \\
1000 mg/dm\({}^{3}\) LI & \(-461.9\) & 26.6 & 0.855 & 85.5 \\
0.1 M HCl & \(-496.2\) & 145.7 & & \\
100 mg/dm\({}^{3}\) LI & \(-490.3\) & 85.6 & 0.412 & 41.2 \\
1000 mg/dm\({}^{3}\) LI & \(-497.9\) & 15.8 & 0.892 & 89.2 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Potentiodynamic polarisation variables for mild steel corrosion in 1 M and 0.1 M HCl in the presence and absence of the inhibitor. Figure 4: Pdp graphs for mild steel in (**a**) 1 M and (**b**) 0.1 M HCl with or without LI. Table 1 presents the polarisation variables for the mild steel in the corrosive and inhibited solutions. The highest shifts in the Ecorr values for _Lawsonia ihernis_ (LI) are 38.5 mV in 1 M HCl and 1.7 mV in 0.1 M HCl. Moreover, there was a notable reduction in the corrosion current density (Icorr) by 156.4 \(\mu\)A/cm\({}^{2}\) in the presence of the LI in 1 M HCl; the reduction was 129.9 \(\mu\)A/cm\({}^{2}\) in 0.1 M HCl. The shift in the Ecorr value and decrease in Icorr signify the effectiveness of the LI in suppressing the corrosion rate of the mild steel under acidic conditions. These changes indicate the potential of the LI to modify the electrochemical characteristics of the metal and fortify its corrosion resistance power in hydrochloric acid solutions. When the shift in Ecorr is below 85 mv, the inhibitor is classified as a mixed inhibitor; values above 85 mv could mean that the inhibitor functioned either as an anodic or a cathodic inhibitor.