Microencapsulation of quinoline and cerium based inhibitors for smart coating application: Anti-corrosion, morphology and adhesion study

In this study, linseed oil-filled urea-formaldehyde-based microcapsules containing cerium acetate (Ce) and 8-Hydroxyquinoleine (8-HQ) were synthesized in an oil-in-water emulsion via in-situ polymerization method. The Field Emission Scanning Electron Microscopy (FE-SEM) and Optical Microscopy (OM) were used to study the shape and morphology of the prepared microcapsule. The results revealed the regular spherical capsules with 20-120 mu m diameters. Prepared microcapsules were dispersed in the epoxy matrix in single (Ce and 8-HQ) and mixed (50 wt.% Ce + 50 wt.% 8-HQ) forms. Electrochemical Impedance Spectroscopy (EIS) and standard salt spray test were conducted to study anti-corrosion properties of different epoxy-based samples on the mild steel substrate. The results revealed improved anti-corrosion and healing performance of microcapsule embedded coating samples compared with their blank counterparts during 28 days exposure to the salt spray test conditions. The sample containing mixed form microcapsules showed the best performance among all samples. After one-week immersion in 3.5 wt.% NaCl electrolyte, vertical bar Z vertical bar at low-frequency value (vertical bar Z vertical bar(lf)) for neat epoxy, 8-HQ, Ce and mixed forms samples decreased from 2.81 x 10(8), 2.70 x 10(9), 1.02 x 10(9) and 8.62 x 10(9) to 1.22 x 10(4), 2.69 x 10(8), 3.40 x 10(7) and 1.98 x 10(9) (ohm. cm(2)), respectively. Finally, fluorescence microscopic study showed that the 8-HQ compound was released at the damaged area on the coated substrate and detects the corrosion phenomenon at the early stage as a smart corrosion indicator.