Synthesis and characterization of hybrid shell microcapsules for anti-corrosion Ni-Co coating

This paper presents the results of the study of microcapsules synthesized using a novel hybrid shell of polyureaformaldehyde/SiO2 (PUF/SiO2) and a core of linseed oil. The synthesis was accomplished by facial polymerization combined with sol-gel of TEOS, and urea-formaldehyde resin to form the hybrid shell under optimal process parameters. The microcapsules were embedded in a metal coating using the electrodeposition method. Microcapsules were characterized by scanning electron microscope (SEM, FE-SEM), energy-dispersive spectroscopy (EDS), particle size analyzer (PSA), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The experimental results indicated that the average size of capsules synthesized umder the optimum processing parameters were in the range of 5 µm to 200 µm with a hybrid shell thickness of less than 1 µm. The internal surface of the shell contained more SiO2 compared to the external PUF/SiO2 layer, as indicated by EDS. While the internal surfaces were smooth, the outer surface of the microcapsules were composed of rough branched-like structures of urea-formaldehyde particles. It was shown by thermal analysis that initial decomposition starts at 225℃ which proved excellent thermal stability. Electrodeposition was carried out with the current density of 25 mA∙cm-2 to embed the synthesized microcapsules into the Ni-Co alloy coating, which was investigated by SEM, and corrosion test (OCP, LP) to characterize the corrosion behavior of these potentially self-healing coatings.