Application of response surface methodology using central composite design for the evaluation of corrosion inhibition performance of <i>Pilliostigma thoningii</i> on mild steel in acidic media

Abstract

Response Surface Methodology (RSM) based on Central Composite Design (CCD) was employed to examine the corrosion inhibition efficiency of pilliostigma thoningii stem bark extract on mild steel in hydrochloric acid solution using gravimetric method. The interactive effects of the inhibitor concentration, temperature and time were optimized for maximum response. The optimum inhibition efficiency of 93.75% at 1.0g/L of inhibitor concentration, temperature of 333K and immersion time of 1h was accomplished. The effectiveness of the inhibitor was also supported using scanning electron microscopy (SEM). Analysis of the results revealed that the adsorption of pilliostigma thoningii extract on the surface of the mild steel was spontaneous and occurred according to physisorption mechanism. The data obtained were fitted into various adsorption isotherms and the mechanism of the interaction was found to conform best to the Langmuir isotherm.