Combination effect of hydro-alcoholic extract of spent coffee grounds (HECG) and Potassium Iodide (KI) on the C38 steel corrosion inhibition in 1M HCl medium: Experimental design by response surface methodology

Abstract This paper introduces Response Surface Methodology (RSM) as a method in order to explore the combination effect of hydro-alcoholic used coffee grounds extract (HECG) and potassium iodide (KI) on the corrosion protection of C38 steel in 1M HCl medium. Open circuit potential (OCP) measurements as a function of time until the steady-state potentials were established. The inhibition efficiency (IE) was defined using electrochemical impedance spectroscopy and potentiodynamic polarization. The obtained results have shown that the influence of the combination of HECG and KI on the inhibition efficiency is statically significant. The addition of 0.007 M KI to 1.0 M HCl solution containing 0.30 g/L of HECG decreases the corrosion of iron steel and improves the performance of HECG by a synergistic effect. The optimum inhibition efficiency was about 97 %, showing a high inhibition efficiency in presence of a combination of the inhibitors (KI + HECG).