Study of the Efficiency of Tetramethylammonium Iodide as a Corrosion Inhibitor for UNS S31803 Duplex Stainless Steel in Hydrochloric Acid Solution

The increasing demand for sustainable and efficient corrosion control strategies has highlighted the potential of ionic liquids as alternative inhibitors due to their excellent properties. This study investigated the corrosion inhibition performance of tetramethylammonium iodide (TMAI) for UNS S31803 duplex stainless steel in 1 M HCl solution. Potentiodynamic polarization tests demonstrated that TMAI significantly reduced the corrosion current density, reaching a maximum inhibition efficiency of 88.1% at 40 °C with a concentration of 5 mM. A modest efficiency reduction was observed at 50 °C, suggesting a decrease in protective layer stability at elevated temperatures. SEM analysis revealed a smoother surface in the presence of the inhibitor, while EDS confirmed the adsorption of TMAI through the detection of characteristic elements. The adsorption behavior followed the Langmuir isotherm. These results demonstrate the effectiveness of TMAI as a corrosion inhibitor and reinforce the potential of ionic liquids for use in aggressive industrial environments.