Biological macromolecule as an eco-friendly high temperature corrosion inhibitor for P110 steel under sweet environment in NACE brine ID196: Experimental and computational approaches

The results of this study reveal the inhibitory performance of biological macromolecules, i.e., maltodextrin (MDL), on P110 steel in NACE brine ID196 solution saturated with CO₂ at 50 °C. The MDL is an environmentally friendly corrosion inhibitor. The inhibitory performance of MDL was investigated using weight loss (WL) tests, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP). The mean and highest deviation from the mean (H. D) of the aforementioned measurements were determined. The results of a computational study predict that neutral MDL molecules exist in the corrosive medium. The EIS findings reveal that charge-transfer resistance is enhanced at high MDL concentrations, demonstrating the protective effect of the MDL molecule. The PDP results suggest that MDL behaves as a cathodic inhibitor. The MDL corrosion inhibition efficiency is 92.4% at 400 mgL^-1. KI (5 mM) is found to enhance the corrosion inhibition efficiency to 95.2% at 300 mgL-1 MDL. The Langmuir model best describes the MDL adsorption process. The AFM results suggest that the average roughness (R_a) decreases from 43 nm (blank) to 10.5 nm using MDL to 8.2 nm using KI + MDL. The results of a contact angle study reveal that the addition of MDL causes the contact angle to increase from 61.28° (blank) to 84.08° (MDL)/92.17° (KI + MDL). The XPS results suggest that hydroxyl (–OH) groups act as strong adsorptive sites. Density functional theory (DFT) results reveal that as the number of glucose units increase, the MDL performance increases.