Dual-cation co-precipitated spherical ZP-based pigments: Enhancing anticorrosive performance of WEP coatings

Abstract

In this work, a novel micro/nanoscale filler with a spherical structure, consisting primarily of NH₄ZnPO₄ and Ce(PO₄) crystals (SNCZP), was successfully prepared by a hydrothermal synthesis method. The synergistic effects of NH₄⁺/Ce³⁺ co-precipitation on the morphological evolution, crystalline characteristics, and phase composition were systematically investigated via SEM, EDS, XRD, FTIR spectroscopy and XPS, respectively. Furthermore, potentiodynamic polarization (PDP) and electrochemical impedance spectroscopy (EIS) measurements were employed to evaluate the physical barrier and inhibitive capacity of the as-obtained pigments. Electrochemical evaluations revealed that the Al substrate pretreated with SNCZP extract exhibited a significant cathodic shift in corrosion potential, accompanied by a distinct reduction in corrosion current density. Notably, the SNCZP-doped waterborne epoxy (WEP) coating demonstrated superior long-term corrosion protection performance: it maintained an initial impedance modulus as high as 2.65 × 10¹⁰ Ω cm² during the early immersion stage (∼7 days) and retained exceptional stability at 3.88 × 10⁹ Ω cm² even after 56 days of immersion. This value remained approximately one order of magnitude greater than that of the spherical zinc phosphate (SZP) doped coating throughout the soaking period. Furthermore, the artificial scratch test further confirmed the self-repair capability of the SNCZP-doped epoxy coating, demonstrating the synergistic effect of chemical passivation and physical barrier protection in mitigating localized corrosion at defect sites. Finally, this study presented a comprehensive investigation into the corrosion protection mechanisms of nanofillers within WEP coatings, elucidating their synergistic effects in enhancing coating durability and substrate preservation.