A bifunctional epoxy coating doped by cerium (III)-8-hydroxyquinoline: Early self-reporting and stimuli-responsive inhibition on corrosion of Al substrate

Recently, anti-corrosion coatings with auto-inhibition and self-reporting on their premature flaws are becoming more and more attractive. In this work, we engineered a cerium nitrate/8-hydroxyquinoline (Ce-HQ) hybrid pigment to endow epoxy coatings with corrosion self-inhibiting and fluorescent self-reporting performances via molecule design. The Ce-HQ pigments were synthesized by physical mixture and then dispersed into the commercial epoxy coating. Once the epoxy coating gets degraded, the underneath aluminum alloy matrix may corrode to produce Al 3+ ions, which can compete with Ce 3+ ions in the Ce-HQ complex, and then chelate with dissociative 8-HQ to form fluorescent Al-HQ complex, due to the higher bonding strength of Al 3+ with 8-HQ than Ce 3+ ions. Thus, not only the responsive releasing of Ce 3+ ions and 8-HQ can inhibit the underlying Al alloy, but the newly formed Al-HQ complex could indicate the location and severity of coating flaws through fluorescent emission under UV light. Electrochemical impedance evidenced that the composite epoxy coating containing 1 % mass Ce-HQ presents high corrosion resistance even after 504 h of salt spray test, showing 90 % corrosion refraining efficiency. This work may enlighten an approach to developing self-healing and self-diagnosis coating for premature corroded Al alloy beneath coatings via reactive release and fluorescent visualization.