Optimization of the inhibition corrosion of carbon steel in an acidic medium by a novel eco-friendly inhibitor Asphodelus ramosus using response surface methodology

Ethyl acetate extract of Asphodelus ramosus (ARAE) was examined as an anti-corrosion agent for carbon steel (CS) in 1 M HCl acid medium using different techniques, namely weight loss method, potentiodynamic polarization, and electrochemical impedance spec­troscopy (EIS) at various temperatures and inhibitor concentrations. An inhibition efficiency of 89.81 % was obtained by the weight loss method at the inhibitor concentration of 700 ppm at 293 K. Increasing the temperature decreases the corrosion inhibition rate. Poten­tiodynamic polarization results showed that the extract is adsorbed on CS surface according to the Freundlich isotherm, while negative values of the standard free energy of adsorption (DG0ads) suggested the physical spontaneity of the adsorption reaction. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) analyses were performed to examine the surface morphology of inhibited and uninhibited CS samples. Central composite design (CCD) based optimization was engaged to analyze factors and maximize inhibition efficiency by applying response surface methodology (RSM) using Design-Expert software.