Application of microcapsules based on a phosphonate inhibitor and porous Al₂O₃ carriers for the anticorrosive modification of polymer coatings

• V.A. Shchelkov¹, S.A. Sidorova^1,2, V.L. Demin¹, S.A. Tyurina² and S.Yu. Rybakov¹

¹ Frumkin Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, 31-4, Leninsky prospect, 119071 Moscow, Russia
² MIREA – Russian Technological University, 78 Vernadsky Ave., 119454 Moscow, Russia

Abstract: This study continues research into the microencapsulation of a phosphonate inhibitor within porous alumina-based carriers and focuses on developing and evaluating the effectiveness of new functional particle formulations. The work addresses the need to prolong the protection of polymer coatings exposed to corrosive chloride-containing environments while preserving their barrier properties. The proposed approach employs closed-type microcapsules synthesized by dry impregnation followed by the thermal curing of the epoxy shell. 1-Hydroxyethane-1,1-diphosphonic acid (HEDP), an effective chelating agent, was used as the inhibitor. Aluminum oxide (Al₂O₃) served as the carrier in two forms, both standard and activated. Microencapsulation isolates the inhibitor from the corrosive environment until the protective coating degrades; this triggers the controlled release of the inhibitor directly at the site of a developing corrosion defect. Electrochemical impedance spectroscopy (EIS) and accelerated corrosion tests (91 and 42 days in 3% NaCl) demonstrated that incorporating 1 wt.% of a microencapsulated corrosion inhibitor (MCI) based on HEDP and activated Al₂O₃ (hereafter act. Al₂O₃) into an epoxy primer led to a two-order-of-magnitude increase in pore resistance R₁ (from 10.7 to 363.8 kΩ·cm²) and a one-order-of-magnitude decrease in coating capacitance CPEc Q0 compared to the unmodified formulation. The observed protective effect stems from the release of the inhibitor and the subsequent formation of microfilaments composed of a sparingly soluble HEDP–Fe complex. These structures block through-thickness microdefects and inhibit chloride ion diffusion toward the steel substrate. SEM and EDS analyses confirmed that phosphorus was predominantly concentrated in the scribe zones, supporting the proposed trigger mechanism for capsule activation.

Keywords: microencapsulation, corrosion inhibitors, polymer coating, corrosion resistance, protective coating, accelerated tests

Int. J. Corros. Scale Inhib., 2026, 15, no. 4, 319-337
doi: 10.17675/2305-6894-2026-15-4-13

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