Adsorption and corrosion inhibition behavior of Pterocarpus marsupium stem extract on mild steel in acid medium: Experimental and Statistical approach

The present work emphasizes the corrosion mitigation behavior of Pterocarpus marsupium stem extract (PMSE) on mild steel (MS) in various concentrations of hydrochloric acid (HCl) solution using an electrochemical technique. The experiments were conducted in three different levels of acid concentrations (0.1, 0.25, and 0.5 M), three levels of inhibitor concentration (0.03, 0.12 and 0.24 g/L), and at three different temperatures (303 to 313 K) and optimized to get maximum inhibition efficiency. The inhibition efficiency increased with an increase in PMSE concentrations in all the acid concentrations and decreased with an increase in temperature. The Tafel polarization technique revealed mixed inhibition behaviour of PMSE with maximum inhibition efficiency (% IE) of 88.9 % at 303 K containing 0.24 g/L of PMSE in 0.1 M HCl solution. The adsorption mechanism of PMSE on the surface of MS is consistent with physisorption by obeying Freundlich’s adsorption isotherm. The corrosion inhibition of PMSE predominantly owing to protective film formation on the metal surface and is confirmed by surface morphological and FTIR spectral studies. RSM studies using the Taguchi method revealed the highest inhibition efficiency to be predicted at minimum temperature and acid concentration and at the maximum inhibitor concentration as obtained in the experiments.