Corrosion inhibition of aluminum alloy in HCl by SDS: experimental, SEM/AFM imaging, and computational insights (DFT and MD simulations).

CONTEXT

The surfactant sodium dodecyl sulfate (SDS) has been investigated for aluminum (Al) corrosion inhibition in 0.2-0.4 M hydrochloric acid (HCl) employing mass loss (ML), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization (PDP) techniques. The inhibition efficiency (IE) of SDS was found to be concentration-dependent, with a maximum of 97% at 8 mM, which was attributed to the presence of long-chain groups. Notably, the highest inhibition efficiencies were recorded at an inhibitor concentration of 8 mM in a 0.2 M HCl solution at 303 K, achieving 97.76% via the gravimetric method, 97.30% through PDP, and 93.72% using EIS analysis. The temperature variation from 303 to 333 K showed that higher SDS concentrations improved the degree of inhibition, whereas higher temperatures reduced the degree of effectiveness. Polarization measurements indicated that SDS exhibited a cathodic inhibition mechanism. A double-layer capacitance (C) was added to an equivalent circuit model for evaluating the electrochemical impedance spectroscopy data. SDS adsorption behaviour followed the Langmuir and Freundlich isotherms as well as the kinetic thermodynamic model. SEM (scanning electron microscopy), EDX (energy-dispersive X-ray spectroscopy), and AFM (atomic force microscopy) proved the protective adsorbed layer of the Al surface.

METHODS

Corrosion resistance of aluminum in SDS-acidic environments was investigated using PDP and EIS methods. Experiments utilized a three-electrode system in which only a 1-mm area of the aluminum sample was exposed, with measurements carried out in 0.2 M HCl solutions (with and without SDS) under controlled conditions, including OCP stabilization, PDP, and EIS with repeated trials to ensure data reliability. The study assessed Al corrosion by measuring weight loss under varying SDS concentrations, immersion times, and temperatures, using precise weighing and standardized calculation methods for inhibition efficiency. Additionally, surface analysis after immersion in corrosive media was carried out using SEM, EDX, and AFM to observe morphological and elemental changes. The Gaussian 09 W software utilizes density functional theory (DFT) for computational studies in this research, applying the B3LYP functional with the 6-311 +  + G (d,p) basis set and conducting a natural bond orbital analysis of sodium dodecyl sulfate (SDS) in both gas and aqueous environments. To enhance the precision, the polarizable continuum model (PCM) was employed, using water as the solvent. The computational tasks were run on a PC with results visualized through Gaussian View 5.0.9, with a focus on parameters such as the HOMO energy, LUMO energy, band gap, and electrophilicity. For the Monte Carlo (MC) and molecular dynamics (MD) simulations, Material Studio 7.0 was used to model interactions between the aluminum surface and an inhibitor molecule in corrosion simulations. The simulations were carried out via an Al (1 1 0) model under periodic boundary conditions, with a simulation box containing ions and molecules in a 0.2 M HCl solution. Multiple cycles of simulated annealing and MD simulations were performed at temperatures ranging from 303 to 333 K, with the COMPASS III force field employed for accurate interaction analysis, including calculating the radial distribution function (RDF).