Corrosion inhibition by naturally occurring Hibiscus sabdariffa plant extract on a mild steel alloy in HCl solution

The corrosion inhibition of mild steel alloys is of tremendous technological importance due to their increased industrial applications. Potentiodynamic polarization and electrochemical impedance spectroscopy techniques were used to establish the effect of different concentrations of HCl on the corrosion behavior of mild steel. A study was conducted on the inhibition of dissolution for a mild steel alloy in the most corrosive concentration of HCl (5 M) by adding different concentrations of aqueous extract of \textit{Hibiscus sabdariffa} plant (named karkade or rosselle) as an ecofriendly inhibitor. The extent of corrosion inhibition as measured by the two techniques was comparable. The results indicated that the additive acts by way of adsorption as an effective protective inhibitor in aggressive acid medium. Curves representing the variation in the extent of adsorption or surface coverage as a function of the concentration of the additive are invariably sigmoid in nature. Generally the inhibition efficiency increases with increasing additive concentration.