Nitrogen-based Cationic Copolymers as Corrosion Inhibitors for P110 Carbon Steel in 20% H2 SO4 : Experimental and Theoretical Studies

The present study demonstrates the corrosion inhibition potential of three nitrogen-based cationic surfactant molecules (AMCs) for P110 carbon steel (P110 CS) in 20% H ₂ SO ₄ solution. The corrosion inhibition efficiency (%IE) of the studied surfactants was demonstrated using electrochemical (OCP, PDP, and EIS), scanning electron microscopy (SEM), and DFT-based computational studies. The outcomes suggest that their inhibition efficiencies increase with increasing hydrophobic character in the form of alkyl chain(s). The surfactant molecule (AMC-3), having two long alkyl chains, manifests the best inhibition efficiency, and AMC-1, without any such alkyl chain, manifests the lowest efficiency. Their %IE followed the sequence (PDP data at 100 ppm): AMC-3 (89.77%) > AMC-2 (93.39%) > AMC-1 (94.44%). Potentiodynamic polarization (PDP) study suggests that they retard anodic and cathodic Tafel reactions and serve as mixed-type corrosion inhibitors. Electrochemical impedance spectroscopy (EIS) study suggests the AMCs become effective by creating a barrier for the charge transfer process through their adsorption at the interface of metal and electrolyte. The adsorption mode of corrosion protection was also supported by SEM analyses, where a significant improvement in the surface morphology of the P110 CS surface was observed in the presence of AMCs, especially in the presence of AMC-3. Their adsorption on the P110 CS surface followed the Langmuir isotherm model. DFT-based quantum chemical calculations show that AMCs interact with the P110 CS surface through physicochemisorption mechanisms where long alkyl chains (or hydrophobicity) play a crucial role in their adsorption.