The electrochemical degradation of carbon steel in acidic media constitutes a significant industrial challenge, necessitating the development of efficient and structurally optimized corrosion inhibitors. This study evaluates the inhibitory efficacy of hexylamine (HA) on carbon steel in 0.1 M hydrochloric acid employing gravimetric measurements across a controlled temperature range of 298–308 K. Inhibition efficiency (IE%) exhibited a direct concentration dependence, attaining a maximum value of 94.9% at 0.025 M and 298 K, while demonstrating a marginal decline with increasing temperature due to partial thermal desorption of the adsorbed film. The interfacial adsorption process conformed precisely to the Langmuir isotherm model at all investigated temperatures, confirming monolayer coverage without significant lateral interactions. Kinetic analysis revealed a systematic increase in apparent activation energy (Eₐ) and enthalpy of activation (ΔHₐ) in the presence of HA, indicative of an elevated energy barrier for anodic metal dissolution and an endothermic corrosion process. Thermodynamic evaluation yielded standard Gibbs free energy of adsorption (ΔG°ₐdₛ) values ranging from −24.20 to −24.64 kJ·mol⁻¹, signifying a spontaneous adsorption process governed by a mixed physisorption–chemisorption mechanism. Furthermore, the enthalpy of adsorption and entropy of adsorption were mechanistically rationalized through a quasi-substitution model, wherein the displacement of multiple pre-adsorbed water molecules by a single hexylamine molecule result in a net increase in interfacial disorder. These findings establish hexylamine as a highly effective, thermodynamically stable inhibitor for mitigating acid-induced corrosion in industrial pickling applications.
Boshra Ahmed Abazid*1 (2026) studied this question.