Corrosion-sensing and self-healing dual-function coating based on 1,10-phenanthroline loaded urea formaldehyde microcapsules for carbon steel protection

In this work, a smart coating with corrosion-sensing and self-healing dual functions was developed on carbon steel by incorporating the urea formaldehyde (UF) microcapsules loaded with 1,10-phenanthroline (Phen) molecules. Phen as both the corrosion-sensing indicator and corrosion inhibitor was encapsulated into the UF microcapsules via the oil-water (O/W) emulsion in-situ polymerization method. When the coating was damaged, the Phen molecules released from UF/Phen microcapsules would react with the Fe2+ ions generated from the active anodic corrosion site of the carbon steel substrate, and displayed a prominent red color chelate compound for corrosion-sensing application. During the neutral salt spray test, the corrosion evolution underneath the damaged coating can be rapidly detected within 15 min. Besides, the corrosion activity near the coating scratch can be effectively inhibited due to the adsorption of released Phen on the exposed substrate surface. After 72 h of immersion in 3.5 wt% NaCl solution, the low frequency impedance modulus of the scratched coating containing 10 wt% UF/Phen microcapsules was almost 7 times that of the scratched blank coating. The smart coating can not only achieve timely corrosion sensing, but also suppress the corrosion activity, which is of great importance for practical corrosion protection applications.