Anticorrosion Effect of Ethoxylate Sulfanilamide Compounds on Carbon Steel in 1 M Hydrochloric Acid: Electrochemical and Theoretical Studies.

Metal corrosion is an important economic problem globally. One of the best ways to protect metal surfaces from corrosion is by the use of corrosion inhibitors, especially surfactants. This study assesses anticorrosion properties of three inhibitor compounds (S1, S2, and S3) of ethoxylate sulfanilamide containing 2, 10, and 20 units of ethylene oxide on carbon steel in 1 M HCl solution. The anticorrosive performance of S1, S2, and S3 was studied using potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), adsorption isotherm, surface tests (scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) spectroscopy, and X-ray diffraction (XRD) analysis), and computational studies (density functional theory (DFT) and molecular dynamics (MD) simulations) within the concentration range of 10-6 to 10-2 M at 30 ± 2 °C. The results of the methods used indicate that increasing the concentration of the inhibitor compounds improves the effectiveness of inhibition (from 50.9 to 98%), whereas the inhibition efficiency order for ethoxylated sulfanilamide compounds is S2 > S3 > S1 with the highest inhibiting efficiency, respectively, of 98.0, 95.0, and 90.0% for 10-2 M. Also, PDP indicated that S1, S2, and S3 inhibitors act as mixed-type inhibitors and their adsorption obeys the Langmuir adsorption isotherm model. Surface tests show that the studied compounds can significantly inhibit acid attack via chemical adsorption on the metal. Furthermore, all of the chemical descriptors derived from DFT indicate that the three inhibitors are quite well adsorbed by the adhesion centers on the CS surface. The three compounds' molecular geometries and electronic structures were calculated using quantum chemical calculations. Using theoretical computations, the energy difference between the highest occupied molecular orbital and the lowest occupied molecular orbital has been determined to represent chemical reactivity and kinetic stability of a composition.