Investigation of Corrosion Inhibition Efficiency of Bitter Leaf Extract on Mild Steel in Acidic Medium

This study investigates the corrosion inhibition efficiency of bitter leaf (Vernonia amygdalina) extract on mild steel in 1 M hydrochloric acid solution, a medium representative of industrial pickling and acid cleaning environments common in Nigerian fabrication workshops. Plant-based corrosion inhibitors have attracted research interest as environmentally benign alternatives to toxic synthetic inhibitors, and Vernonia amygdalina is abundantly available across Nigeria's southern and middle belt zones. Bitter leaf extract is prepared by aqueous maceration and characterised by FTIR spectroscopy to identify functional groups responsible for adsorption on the steel surface. Weight loss measurements are conducted at temperatures of 30, 40, 50, and 60 degrees Celsius over 2, 4, 6, 8, and 24 hour immersion periods at extract concentrations of 100, 250, 500, 750, and 1000 mg/L. Electrochemical measurements including potentiodynamic polarisation and electrochemical impedance spectroscopy are performed in a three-electrode cell setup. Results show a maximum inhibition efficiency of 91.3 percent at 1000 mg/L and 30 degrees Celsius. Inhibition efficiency decreases with temperature, indicating a physical adsorption mechanism confirmed by calculated activation energy values. Polarisation curves classify the extract as a mixed-type inhibitor. Adsorption obeys the Langmuir isotherm. The study recommends further investigation of bitter leaf extract in combination with surfactants to improve high-temperature performance. Keywords: corrosion inhibition, bitter leaf extract, mild steel, hydrochloric acid, green inhibitor.