Mild steel corrosion inhibition in hydrochloric acid using cocoa pod husk-Ficus exasperata: extract preparation optimization and characterization

This paper aimed at studying optimization of cocoa pod-Ficus exasperate (CP-FE) extract preparation as mild steel anticorrosive agent in hydrochloric acid solution using central composite design as optimization tool. Maximum inhibition efficiency of 95.42% was obtained at ethanol volume, extraction time, CP-FE mixing ratio and CP-FE mass of 500 ml, 48 hr, 5 and 100 g respectively. Coefficient of determination value of 0.9674 between experimental and predicted values suggested that the model developed was exact. Optimum predicted point for CP-FE extract preparation by CCD was 62.02 ml, 9.51 hr, 3.42 and 75.68 g for the ethanol volume, extraction time, CP-FE mixing ratio and CP-FE mass respectively. SEM images revealed acid attack on mild steel surface. Adsorption of CP-FE extracts on mild steel surface prevents acid attack. FTIR revealed presence of carboxyl (-COOH) and hydroxyl (-OH) functional groups. EDS revealed high iron composition on mild steel surface in the presence of CP-FE extracts. Loss of Fe2+ into free HCl solution was observed from the AAS result. Conclusively, mixed cocoa pod-Ficus exasperate extracts exhibited effective corrosion inhibitory attributes for mild steel in HCl solution.