Electrochemical and quantum chemical studies on the corrosion inhibition of 1037 carbon steel by different types of surfactants

In this work, three different types of surfactants, namely, dodecyl trimethyl ammonium chloride (DTAC, C12H25N (CH3)(3)Cl)(-), octyl phenol poly(ethylene glycol ether)(x) (TX-100, C34H62O11 for x = 10) and dioctyl sodium sulfosuccinate (AOT-100, C20H37O7NaS) with corrosion restraint were utilized as corrosion inhibitors for 1037 CS in 0.5 M HCl. The protection efficacy (% IE) was indicated by weight loss and electrochemical measurements. Polarization curves showed that the investigated compounds are mixed-type inhibitors. The protection efficacy (% IE) increases with the increase in the surfactant concentration and reached 64.42-86.46% at 8 x 10(-4) M and 30 degrees C. Adsorption of these utilized surfactants (DTAC, TX-100, and AOT) onto the CS surface concurred with the Langmuir adsorption isotherm. Impedance data revealed that by increasing the surfactant concentration, the charge transfer resistance (R-ct) increases and vice versa for the capacitance of double layer (C-dl). Surface morphological investigations such as scanning electron microscopy (SEM) combined with EDX and atomic force microscopy (AFM) were used to further investigate the inhibitors' protective abilities. Monte Carlo simulations showed the great interaction between the tested surfactants and the metal surface of the CS. The theoretical results (density functional theory, DFT) were in good agreement with experimental measurements. The restraint efficiencies of anionic, neutral, and cationic surfactants regarded a certain dating to HSAB precept and Fukui indices.