Effect of temperature, concentration, and synergism on the inhibition behavior of Opuntia ficus-indica mucilage for P11 steel corrosion in 1 M HCl solution

The aim of this study was to investigate Opuntia ficus-indica mucilage (OFIM) as a corrosion inhibitor alone and in combination with KI for P11 steel in 1 M HCl solution at 25, 45, and 65°C, using potentiodynamic polarization curves (PDP), linear polarization resistance (LPR), electrochemical frequency modulation (EFM), electrochemical impedance spectroscopy (EIS), and gravimetric tests.The OFIM inhibition efficiency increases with inhibitor concentration and with temperature, from 25 to 65°C.The PDP results revealed that OFIM acts as a mixed-type inhibitor.According to the EIS results, OFIM has a maximum inhibition efficiency of 72.3% at 65°C with a concentration of 1 g/L.Among the isotherms tested, the OFIM adsorption on the P11 steel surface obeys the Langmuir adsorption isotherm.The thermodynamic parameters of adsorption and activation support a mixed physical and chemical adsorption process.The OFIM/KI mixture substantially enhances the corrosion inhibition efficiency at temperatures from 25 to 65°C.The EIS results showed that 1 g/L OFIM and 5 mM KI had a maximum inhibition efficiency of 88.5% at 65°C.Electrochemical and gravimetric tests show that the inhibition efficiency follows the order: OFIM/KI > KI > OFIM.The synergistic effect of KI was determined by calculating the synergy parameters.This showed that there is a competitive co-adsorption mechanism between the iodide anion and OFIM cations.