Synthesis of 1, 4, 7-triazaheptane derivative and its corrosion inhibition for mild steel in the hydrochloric medium

Abstract

To exploit the advanced corrosion inhibitor for mild steel in acidic solution, N, N, N, N, N′-pentakis (2-hydroxyethyl)-1,4,7-triazaheptane (PHET) was synthesized by a facile process, which was confirmed by FT-IR, NMR and EI-MS. Inhibition effect of PHET was examined on mild steel in 1.0 M HCl solution by using weight loss, electrochemical tests and surface analyses. The results showed that the optimal concentration of PHET in HCl solution was 400 mg/L corresponding to the inhibitive efficiency of 93% at 293 K. PHET presented superior and durable corrosion inhibition performance for mild steel. Meanwhile, PHET acted as a mixed-type inhibitor which affects both anodic and cathodic reactions of the corrosion process. PHET could be absorbed on mild steel through forming complexes with ferrous ions that acted as protective film, which was supported by UV–vis and XPS analyses. The adsorption process of PHET molecules on mild steel, following Langmuir adsorption isotherm, was an exothermal process and belonged to mixed adsorption mechanisms (ΔGads°=-31.78 kJ mol−1, 293 K) between physisorption and chemisorption. Besides, theoretical calculations were conducted to give further investigation on the inhibition mechanism of PHET and elucidated the adsorption behaviour of PHET. PHET synthesized in this work also can be extended to use for the corrosion protection of other metals in acidic medium.