Dual-Functionality of Henna <em>(Lawsonia inermis)</em> Leaf Extract as a Dispersant and Green Corrosion Inhibitor in a Water-Borne Silicate Coating

This study investigated the effect of Lawsonia inermis extract as a natural additive to improve the performance of zinc-rich silicate-based coatings on carbon steel. The paint films were prepared with extract concentrations of 0-12 wt% and analyzed by FTIR, XRD, XRF, SEM. The corrosion resistance was evaluated by electrochemical measurements (EIS, potentiodynamic polarization) after 35 days of immersion in 3.5 wt% NaCl solution. The results indicated that a 5 wt% concentration was optimal, as it improved the microstructure of the paint film, leading to a denser and more homogeneous coating. Electrochemical measurements confirmed that this sample exhibited the highest impedance and polarization resistance after testing, which demonstrates enhanced corrosion resistance. The study concluded that the henna extract serves a dual role as both a corrosion inhibitor and a microstructure modifier. The use of natural additives at optimal concentrations is considered a potential approach to improve the effectiveness of protective coating systems.