Innovative phosphorus-containing epoxy resins: A new approach to acidic corrosion protection

The main challenges in the corrosion field for steel include its high susceptibility to acidic degradation and the need for sustainable and efficient corrosion inhibitors. The main objective was to synthesize a novel phosphorus-containing trifunctional epoxy resin, named phosphoric ester triglycidyl ether hydroquinone (TGEHEP), through a two-step process. Initially, the intermediate known as phosphoric ester trihydroquinone was synthesized. Subsequently, epichlorohydrin was added in the second step to produce the new TGEHEP epoxy resin. For the structural characterization of this compound, FTIR, 1H and 13C NMR were used. These techniques confirmed the final chemical structure of the synthesized macromolecule. The newly developed TGEHEP epoxy resin was subsequently utilized as a protective agent for carbon steel in 1.0 M HCl. This study incorporated various techniques, including PDP, EIS, EFM, DFT, MC, and MD simulations. Additionally, SEM/EDS was applied to examine the surface. These methods allowed us to analyse the surface structure and chemical composition of the sample, providing further insights into the adsorption process and corrosion protection mechanism. Electrochemical test results revealed that the TGEHEP concentration significantly enhanced protection. Notably, EIS demonstrated an outstanding protection efficiency of 96.70% with 10−3 M TGEHEP epoxy resin. The polarization findings also indicate that the resin acts as a mixed inhibitor. In line with the Langmuir isotherm, epoxy resin was effectively used to protect the metal surface. Furthermore, thermodynamic kinetic parameters were estimated to evaluate the adsorption of the inhibitor. TGEHEP showed a greater adsorption energy (-195.05 kcal/mol) than did its protonated form (-178.65 kcal/mol), indicating that the interaction with the iron surface was stronger in its neutral form. A significant increase in the concentration of TGEHEP was detected, reaching a maximum of 762.4 Ω.cm² at a concentration of 10−3 M. This suggests that TGEHEP forms a barrier that impedes electron transfer, a key factor in corrosion processes. The ΔGads is −44.3 kJ/mol, which is within the typical range for chemisorption. This suggests that the adsorption of TGEHEP onto the metal surface includes more than just physical adsorption; it likely involves electron transfer, which is characteristic of a chemisorptive bond. Comparatively, TGEHEP demonstrates superior performance to previously published corrosion inhibitors, with its efficacy not only attributed to its unique chemical structure but also to its environmentally benign nature.