Corrosion inhibition of mild steel in 1M HCl using Tamarindus indica extract: electrochemical, surface and spectroscopic studies

We report, here, the corrosion inhibition of mild steel specimen in 1M HCl by tamarind fruit pulp aqueous (TFPA) extract. The inhibition property in the presence of TFPA extract is studied using weight loss, polarization measurement and electrochemical impedance spectroscopy (EIS). The inhibitor efficiency is found to vary from 74% to 88% (weight loss method) with TFPA concentration of 100-600ppm. The reduction in Tafel slopes shows that TFPA acts as a mixed-type inhibitor. The adsorption of the inhibitor on the metal surface follows Langmuir isotherm. The standard Gibbs free energy of adsorption value of -40kJ/mol suggests the chemisorption of inhibitor molecules via coordinate bond. AFM results exhibit a decrease in the surface roughness of mild steel, exposed to 1M HCl from 299 +/- 12 to 154 +/- 6.6nm, with increasing concentration of inhibitor from 0 to 600ppm due to the uniform coverage of inhibitor molecules on the metal surface. X-ray photoelectron spectroscopy de-convoluted high resolution profiles of C 1s (carbon) for mild steel exposed to 1M HCl with 600ppm inhibitor show major peaks corresponding to sp(3) C-C/C-H (284.9eV) and oxygen bondings in C-OH, C=O, COOH with a binding energy of 285.9, 286.9, 288.5eV, respectively, thereby confirming the adsorption of organic moieties on mild steel surface. Fourier transform infrared spectroscopy further confirms the adsorption of inhibitor molecules on the metal surface. Therefore, tamarind fruit pulp extract is a potential corrosion inhibitor for mild steel, which is cost-effective, green and non-toxic.