Encapsulated Corrosion Inhibitive Pigment for Smart Epoxy Coating Development: An Investigation of Leaching Behavior of Inhibitive Ions

A comparative study between the leaching behavior of inhibitive ions from conventionally pigmented and smart (with encapsulated pigments) epoxy coatings has been conducted. Leaching of calcium phosphate as an inhibitive pigment from epoxy coatings was tested in 3.5 wt % NaCl solution. The results showed that pigment encapsulation contributed to a more uniform and stable coating microstructure based on the Scanning Electron Microscopy–Energy-Dispersive X-ray Spectroscopy (SEM-EDX) analysis and a higher leaching rate of the inhibitive pigment via the Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) analysis, thereby enhancing both the active corrosion protection and the barrier properties of the coating film. This was further verified by the Electrochemical Impedance Spectroscopy (EIS) measurements. After 7 days of immersion in 3.5 wt % NaCl solution, the coating resistance of the smart epoxy coating with mesoporous silica nanoparticle encapsulated calcium phosphate (MSN-CP3%) was 2 × 10⁹ Ω·cm² compared to 1.1 × 10⁶ Ω·cm² and 2.6 × 10⁶ Ω·cm² for the conventional epoxy coatings pigmented with 3 wt % and 5 wt % calcium phosphate (CP3% and CP5%), respectively.