Inhibitive Properties of Acanthospermum hispidum Dc Leaves Extracts on Corrosion of Mild Steel in 1M HCl solution

This study was conducted to investigate the suitability of Acanthospermum hispidum Dc leaves extracts for corrosion inhibition of mild steel immersed in 1M HCl solution using gravimetric and potentiodynamic polarization methods. The study was conducted at room and elevated temperatures of 313, 323, 333 and 343K. The test period was varied from 24 to 168hrs at 24hrs interval, at room temperature and 3 hours at each elevated temperature. The experiments were performed with inhibitor concentrations of 0.1, 0.2, 0.3, 0.4 and 0.5 g/L. The results showed that the corrosion rates increased with time of immersion in the absence of inhibitor but decreased with inhibitor concentration at room and elevated temperature, while inhibition efficiency increased with increase in inhibitor concentration at room temperature but decreased with temperature rise. .Inhibition efficiency of 80 % for leaves extracts was achieved at 0.5 g/L at room temperature but decreased to 66.67 % at 0.5 g/L and temperature of 343K implying desorption of inhibitor at higher temperature. Potentiodynamic polarization method was used to see the influence of the extracts on the anodic dissolution of mild steel. The results showed that the extracts acted as mixed type inhibitor by moderating both the anodic and cathodic reactions and remarkably lowered corrosion rates from 10.889 to 0.365 mm/yr. The absorption of the extracts on the metal surface obeyed Langmuir and Temkin isotherms. The thermodynamic parameters evaluated gave negative values of ∆G°ads in the range of -21.35 to – 22.82 kJ/mol. which is less than 40 kJ/mol indicating physical absorption of the extracts on the metal surface. The increasing values of Ea (kJ/mol) from 24.21 to 47.88 kJ/mol also confirms that absorption is by physisorption mechanism.