Adsorption mechanism and inhibition efficiency of quaternium-15 (Q15) surfactant on carbon steel in 1 M HCl: A combined theoretical and experimental approach

Quaternium-15 (Q-15) is widely used not only in cosmetic products but also in various industrial applications such as glues, adhesives, emulsifiable metal-cutting fluids, latex and emulsion paints, floor polishes, and floor waxes. This study investigates the corrosion inhibition performance of Q-15 at varying concentrations on carbon steel in 1 M HCl solution over a temperature range of 20–50 °C using multiple electrochemical techniques. Both thermodynamic and kinetic analyses demonstrate that the corrosion inhibition efficiency increases with Q-15 concentration, achieving an average protection rate of 85% at 50 °C, which further improves to 95.51% at 794 ppm. Electrochemical results reveal that Q-15 acts as a mixed-type inhibitor by reducing both anodic and cathodic current densities. The adsorption of Q-15 on carbon steel surfaces follows the Langmuir isotherm model. Surface characterization by atomic force microscopy (AFM) and scanning electron microscopy (SEM) confirms a significant reduction in surface roughness and defects after treatment with Q-15. X-ray photoelectron spectroscopy (XPS) analysis detects Fe–N bonding, confirming the adsorption of Q-15 molecules at the steel interface. Furthermore, quantum chemical calculations and molecular dynamic simulations provide molecular-level insight into the strong corrosion inhibition capability and adsorption mechanism of Q-15 on the Fe (111) surface.

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