Acid-phase protection of carbon steel by lauramidopropyl amine oxide: evidenced by ICP-AES, electrochemical methods, severe-condition testing, and atomistic modeling

The corrosion-inhibition performance of commercial lauramidopropyl amine oxide (LAO) toward carbon steel in 0.5 M HCl was evaluated through a combined experimental and computational workflow. Dissolved metal release was quantified by ICP-AES, while potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS), and linear polarization resistance (LPR) were used to probe the interfacial electrochemical response at 293 K. LAO suppressed steel dissolution in a concentration-dependent manner. Based on ICP-AES, the inhibition efficiency increased from 76.5% at 50 ppm to 85.5% at 600 ppm. Electrochemical methods showed the same trend, and at 1200 ppm the inhibition efficiency reached 95.0%, 97.6%, and 97.5% according to PDP, EIS, and LPR, respectively. The small displacement in corrosion potential indicates mixed-type inhibition, whereas the marked increase in charge-transfer resistance and the decrease in double-layer capacitance support the formation of an adsorbed protective layer. Adsorption analysis was consistent with Langmuir-type behavior after converting the inhibitor concentration to molar active-LAO units and afforded ΔG°_ads ≈ - 37.9 kJ mol^- 1, indicating spontaneous and strong interfacial affinity, while the non-unity Langmuir slope indicates non-ideal adsorption. Temperature-dependent ICP-AES measurements between 293 and 333 K showed increasing corrosion rate with increasing temperature, but retained measurable inhibition at 150 ppm. In contrast, under severe gas-pressurized rotating-vessel conditions at 150 °C, 150 ppm LAO delivered only 27.9% inhibition, demonstrating that room-temperature efficacy does not translate directly to harsh service. To rationalize the adsorption tendency, density functional theory (B3LYP/6-31 + G(d, p)) and Monte Carlo simulations on Fe (110) were performed. The calculated descriptors (EHOMO = - 8.12 eV, ELUMO = - 2.72 eV, ΔE = 5.40 eV, dipole moment = 5.1 D) support favorable interfacial reactivity, while the Monte Carlo adsorption energy (- 175.27 kcal mol - 1) indicates strong adsorption on an idealized iron surface. Taken together, the data identify LAO as an efficient ambient-condition acid inhibitor for carbon steel, while also defining its limitations under high-temperature rotating-vessel conditions.