Enhanced long-term corrosion resistance and self-healing of epoxy coating with HQ-Zn-PA nanocomposite

Abstract

This study developed a self-healing, anti-corrosive coating based on a novel nanocomposite formulation of 8-hydroxyquinoline-5-sulfonic acid-zinc doped polyaniline (HQZn-PA) incorporated into an epoxy matrix. The chemical composition and surface morphology of the synthesized nanocomposite were thoroughly characterized using Fourier transform infrared spectroscopy, X-ray diffraction, nuclear magnetic resonance, and scanning electron microscopy. Electrochemical impedance spectroscopy and potentiodynamic polarization tests confirmed the outstanding corrosion resistance and self-healing efficiency of the coating. The synthesized HQZn-PA demonstrates enhanced anticorrosive properties through the synergistic effects of its constituents. Polyaniline (PA) contributes anodic protection and forms a barrier layer, while the chelation of zinc by 8-hydroxyquinoline-5-sulfonic acid (HQZn) improves PA compatibility within the polymer matrix and functions as an organic corrosion inhibitor. This dual action strengthens corrosion resistance through both anodic and cathodic protection mechanisms. The HQZn-PA nanocomposite reduced the corrosion rate of epoxy coating by 450× compared and maintained an impedance modulus of 1.03 × 10¹⁰ Ω cm² after 40 days in a saline environment. The nanocomposite also demonstrated a self-healing efficiency of 99.28% in scratched coatings. These results highlight the potential of HQZn-PA as a highly effective corrosion inhibitor and self-healing agent for long-term metal protection in harsh environments.

Keywords: 8-Hydroxyquinoline-5-sulfonic acid; Anti-corrosion; Nanocomposite coating; Polyaniline; Self-healing.

Fig. 1

(a) FTIR spectra of CPA, HQZn, and HQZn-PA (b) XRD patterns of CPA, HQZn, and PA-HQZn, and (c) 1H NMR spectrum of HQZn-PA.

Fig. 2

SEM images of HQZn (a, b), CPA (c, d), HQZn-PA (e, f) and EDS elemental images of HQZn-PA (g–k).

Fig. 3

Bode (left) and Nyquist (right) diagrams illustrating the response of steel plates immersed in blank solution (a, b), solutions containing CPA (c, d) and HQZn-PA extracts (e, f).

Fig. 4

(a) PPCs of steel plates after 48 h of immersion in the blank, CPA and HQZn-PA extracts saline solutions, (b–d) SEM images of bare steel after 48 h submerging in HQZn-PA extract in 3.5 wt% of NaCl solution and EDS elemental images of HQZn-PA (e–i).

Fig. 5

Schematic diagram of the corrosion protection mechanism of HQZn-PA nanocomposites.

Fig. 6

Bode (left) and Nyquist (right) plots of (a, a′) EC, (b, b′) NC1, (c, c′) NC2, (d, d′) NC3 and (e, e′) NC4 submerged in the 3.5 wt% NaCl solution.

Fig. 6

Bode (left) and Nyquist (right) plots of (a, a′) EC, (b, b′) NC1, (c, c′) NC2, (d, d′) NC3 and (e, e′) NC4 submerged in the 3.5 wt% NaCl solution.

Fig. 7

Surface morphology of NC2 (a–c), NC3 (d–f) coatings after immersion in a 3.5% NaCl solution for 21 days.

Fig. 8

Equivalent circuit models of the prepared coatings.

Fig. 9

Bode and Nyquist diagrams of scratched coatings (a, a′) EC, (b, b′) NC2 and (c, c′) NC4.

Fig. 10

SEM images (a–c), and EDS elemental characterizations (d–g) of the scratched region on the steel surface of the NC2.