# _Laasonia inermis_ as an Active Corrosion Inhibitor for Mild Steel in Hydrochloric Acid
## 3 Results and Discussion  
### Gravimetric Results  
In Figure 1, the corrosion rate reduced significantly as the concentration increased from 100 mg/dm\({}^{3}\) to 3000 mg/dm\({}^{3}\), that is, from 8.4259 to 0.0576 for 0.1 M HCl and from 0.034 mdd to 0.0121 mdd in 1 M HCl, respectively. At the higher concentrations of 2000 mg/dm\({}^{3}\) and 3000 mg/L, the corrosion rates approach zero, thus indicating good corrosion inhibition of mild steel at the studied concentrations. The significant reduction in the corrosion rate observed with increasing inhibitor concentrations (from 100 mg/dm\({}^{3}\) to 3000 mg/dm\({}^{3}\)) for mild steel exposed to 0.1 M and 1 M HCl solutions highlights the effectiveness of the corrosion inhibitor in mitigating corrosion. This phenomenon can be attributed to the adsorption of the inhibitor molecules (for example, hexadecanoic acid-2,3-dihydroxy ester and hexadecanoic ethyl ester) on the metal surface, forming a protective barrier that inhibits the corrosion process. In acidic environments, like hydrochloric acid (HCl), mild steel is susceptible to rapid corrosion due to the dissolution of iron ions (Fe\({}^{2+}\)) in the solution. However, when corrosion inhibitors are introduced to the solution, they interact with the metal surface through physical or chemical adsorption, hindering the electrochemical reactions responsible for corrosion. The mechanism of the adsorption of the _Lawsonia intermis_ extract is an interplay between physisorption and chemisorption. At the initial time, the LI extract first adheres physically to the surface of the mild steel through weak van der Waals forces. However, as the contact continues over time, some of the molecules may chemisorb by the formation of strong covalent or ionic bonds between the iron atoms in mild steel and hydroxyl and carbonyl groups in the identified compounds. The inhibitor molecules may block active sites on the metal surface, preventing aggressive species, like H\({}^{+}\) ions, from accessing and reacting with the metal. The observed corrosion rates of 8.4259 mdd reducing to 0.0576 mdd for 0.1 M HCl and from 0.034 mdd to 0.0121 mdd for 1 M HCl at higher inhibitor concentrations (2000 mg/dm\({}^{3}\) and 3000 mg/dm\({}^{3}\)), approaching zero, suggest that the corrosion inhibition efficiency is quite high. A corrosion rate approaching zero indicates the effective protection of the mild steel, as the inhibitor is able to significantly reduce the rate of metal loss due to corrosion. Figure 1 shows that the weight loss of the metal coupons is lowered in the presence of _Lawsonia intermis_ when compared with the blank solution. It is shown that the loss in the weight of the coupons reduces at all the various concentrations of the inhibitor, indicating good corrosion inhibition performance. [PERSON], [PERSON], and [PERSON] (2016) also observed a similar trend of behaviour when they studied the corrosion inhibitory effect of elephant grass (_Pennisetum purpureum_) extract on mild steel corrosion in a 1 M HCl solution by employing the mass loss technique. The results of their work showed that mass loss and corrosion rates decreased as the concentration of the extract was raised. The work of [PERSON], [PERSON], [PERSON], [PERSON], and [PERSON] (2014) confirmed a similar behaviour, as it was observed that the extract of _Terminalia chebula_ inhibited the corrosion of mild steel in acidic media. The work of [PERSON] (2015) also found Hibiscus sabdarifa extract to slow the corrosion of mild steel in 2 M hydrochloric and 1 M sulphuric acidic solutions. In Figure 2, there was no significant weight loss over time for the different concentrations of the _Lawsonia intermis_, thus signifying the stability of the inhibitor with respect to time under the studied environmental conditions. This shows that the inhibitor is stable under the studied conditions with respect to time.