Abstract
Metal-organic network cross-linking agents are commingled with epoxy for establishing multi-functional coating system with robust resistance properties for steel protection applications in harsh atmospheres. To support this concept, the present study relates to fabrication of new mixed ligand Cu(II) and Zr(IV) complexes of metformin (MF) and 2.2' bipyridine (bpy) as coating surface cross-linking modifiers to guard the steel surface of petroleum platforms from corrosion in severe environments. CHN analysis, molar conductance, magnetic susceptibility, FT-IR, UV-Visible, H-1 NMR and TGA/DTG analysis were performed for full characterizations of the two ligands and their mixed complexes. The elemental analysis data affirmed the chemical formula of the formed complexes. Molar conductance measurements proved that the complexes were electrolytic in nature with 1:2 (metal:ligand) molar ratio. The FT-IR analysis for MF, bpy and their complexes manifested that MF and bpy chelated with metal ions as bidentate ligands through two imines (-C = NH) groups in MF and through two nitrogen of pyridine rings in bpy. The TGA/DTG analysis demonstrated the thermal stability and decomposition of the complexes. The magnetic moment measurements offered paramagnetic properties for Cu(II), mu(eff) = 1.70 B.M. The structure geometry survey affirmed a distorted octahedral geometry of the formed Cu(II) and Zr(IV) complexes. Epoxy coating formulations loaded with the same concentration of MF, bpy, Cu(II), and Zr(IV) compounds were applied and evaluated. Salt spray corrosion trial demonstrated that PA-DGEBA/ MC-Cu coating achieved advanced corrosion mitigation demeanor at blistering size of #8, few frequency and calculated rust grade at 10. SEM morphology and EDX analysis were performed to explicate the protective performance in which PA-DGEBA/MC-Cu coated layer displayed the least Fe peak count at 2.5 without appearance of rusting. AFM microstructure of surface-modified Cu(II) epoxy coating offered the most smooth surface (Ra = 1.78 nm, Rq = 2.99 nm), with a harder matrix and perfect nonporous coating surface. Acid spot test checked the chemical resistance of these coatings and elucidated that DGEBA/MC-Cu coating achieved the highest acid resistances at Level 0 by H2SO4 (96%), HNO3 (70%) and HCl (37%) against full deterioration of blank neat epoxy at Level 3. (C) 2021 The Author(s). Published by Elsevier B.V. on behalf of King Saud University.