Self-repairing Anticorrosive Coatings for Rusty Substrates

Metals are prone to corrosion in marine environments. Therefore, it is very important to study the methods to prevent or slow down metal corrosion to increase the service life of metals. Protecting metals by organic coating is the most economical and widely used method. With tung oil as the core and urea-formaldehyde resin as the wall material, the in-situ polymerization method was used to prepare microcapsules suitable for surface coating of rusty metal. The preparation process of microcapsules was studied, and a coating for repairing corroded metal parts in marine environment was prepared by adjusting the preparation formula. The epoxy resin, xylene and ethanol were evenly mixed in a beaker at 50 ℃. Grinding powders of aluminum tripolyphosphate, zinc phosphate and ferric oxide were added into a beaker and used as functional fillers. Then, the penetrant, rust transforming agent, dispersant, leveling agent and defoaming agent were used as additives and added into the beaker. The beaker was sealed and the resulting mixture was stirred at 50 ℃ for 0.5 h. Next, the prepared microcapsules (0%, 5%, 10%, 15%, 20%, 25% and 30% mass fraction) and T31 curing agent were uniformly added into the above mixture. The coating was coated on the rusty tinplate substrate and cured at 25 ℃ for 24 h. The tinplate was soaked in 3.5wt.% NaCl solution for 5 days. The rusty tinplate substrate was polished with 400 mesh sandpaper to make the rust layer smooth, and then coated. A coating with a thickness of about 300 μm was prepared. The surface morphology and wall thickness of microcapsules were observed by scanning electron microscope. The chemical structures of microcapsules, urea-formaldehyde resin and tung oil were determined by Fourier transform infrared spectroscopy, and the materials in the scratch repair area were compared with those in the cured tung oil by infrared spectroscopy. Thermogravimetric analysis (TGA) was used to characterize the UF-tung oil microcapsules, tung oil and separated capsule wall samples. The mass fraction of the microcapsule core was calculated. The self-repairing process of the coating was observed by scanning electron microscope and energy dispersive spectrometer. Scanning Kelvin probe was used to study the change of potential distribution around the scratch area during self-repairing recombination. Electrochemical impedance spectroscopy (EIS) was used to explore the corrosion resistance of the coating. The sample was pit in a salt spray test box for salt spray test. The mean particle diameter of the prepared microcapsules was (47.37±9.41) μm, where the mass fraction of the core (tung oil) was up to 81.57wt.%. The coatings containing 20wt.% microcapsules possessed an excellent self-healing performance and corrosion resistance. The scratched coatings were able to be self-repaired completely within 24 h. Scanning electron observations of the coating and scanning Kelvin probes confirmed that the scratched area was self-healing and the coating could resist corrosion for a long time. Thus, they could be used to significantly extend the service life of coatings. The innovative self-healing technology is expected to find potential applications in anticorrosive coating systems. The coatings can be applied directly on rusty metal surfaces, reducing the cost of coating metal parts in complex application environments. © 2024 Chongqing Wujiu Periodicals Press. All rights reserved.