Preparation And Anti-Corrosion Properties Of ZIFs-Based Self-Healing Epoxy Coatings On The Carbon Steel Surface

Carbon steel is widely used in important industrial production fields such as aerospace,shipbuilding,oil pipelines and so on due to its advantages of low price,good mechanical properties,and excellent durability.However,harsh external environments such as high humidity and salt can accelerate the corrosion of carbon steel.In order to mitigate the detrimental impact of corrosion on the economy and environment,it is considered as an effective method to apply intelligent organic coatings on the metal surface.Added with nanocontainers loaded with corrosion inhibitors,the smart organic coating is endowed with both active and passive anti-corrosion performance.In this thesis,zeolitic imidazolate frameworks（ZIFs）were selected as nanocontainers to encapsulate green low-toxicity corrosion inhibitors.A series of pH-responsive ZIFs-based composite materials were prepared and further added into epoxy resin to construct pH-responsive self-healing anti-corrosion organic coatings on the surface of carbon steel.The corrosion protection performance and self-healing mechanism of these composite coatings were investigated.The main content is as follows:ZIF-8-based composite materials（I-BZ and II-BZ）loaded with benzotriazole（BTA）were prepared using one pot method and two-step vacuum impregnation method,respectively.Then,I-PBZ and II-PBZ core-shell composite materials were encapsulated with polydopamine（PDA）to improve the utilization efficiency of BTA corrosion inhibitor.Two pH responsive self-healing protective coatings（I-PBZ-EP and II-PBZ-EP）were constructed on the surface of carbon steel.ZIF-8 as filler was used to construct ZIF-8-EP coating on the carbon steel surface.The effect of the addition amounts of ZIF-8（0.1 wt.%,0.3 wt.%and 0.5 wt.%）on the anti-corrosion properties of the EP coating.The results of electrochemical impedance spectroscopy（EIS）shows that the corrosion protection performance of the EP coating with addition of 0.3 wt.%ZIF-8 is superior to the other two.The release process of BTA was studied using UV-vis spectroscopy.The results show that both I-PBZ and II-PBZ composite materials have pH stimuli-responsive release abilities,and the release amount of BTA in I-PBZ was higher than II-PBZ.The EIS results show that the low-frequency impedance modulus(|Z|_0.01Hz)of the I-PBZ-EP coating remains at 2.16×10¹⁰Ω?cm² immersed in a 3.5wt%Na Cl solution after 35days,suggesting that the I-PBZ-EP coating has excellent corrosion resistance.|Z|_0.01Hz of the scratched I-PBZ-EP and II-PBZ-EP coatings shows multiple trends of first decreasing and then increasing within 13 hours of immersion,indicating that I-PBZ-EP and II-PBZ-EP have self-healing properties.Finally,the pH stimuli-responsive self-healing mechanism is proposed.The two-dimensional/three-dimensional integrated structural composite（PZZ）was prepared by ZIF-8 nanoparticles in-situ grown on the surface of ZIF-L nanosheets（PZ）loaded with proline corrosion inhibitor.The PZZ epoxy coating（PZZ-EP）with active and passive corrosion resistance was constructed on the surface of carbon steel.The passive barrier effect of ZIF-L nanosheets in EP coating is attributed to the ZIF-L sheet-like structure,which provides the coating with"labyrinth effect"and prolongs the penetration path of corrosive media.The results of transmission electron microscopy（TEM）and X-ray diffraction（XRD）indicate that PZZ has multidimensional core-shell structure.The EIS results show that|Z|_0.01Hz of PZZ-EP immersed in a 3.5wt%Na Cl solution still maintains at 3.9×10¹⁰Ω?cm² after 35 days,showing that PZZ-EP coating has long-term corrosion protection abilities for carbon steel and prolongs its service life.The active and passive anti-corrosion mechanism of PZZ-EP is explored.The self-healing coating（MHZ-EP）with pH stimuli-responsive release was constructed on the surface of carbon steel.MHZ composite materials were prepared using ZIF-8 as a nanocontainer loaded with sodium molybdate and histidine corrosion inhibitors.The loading of sodium molybdate and histidine in MHZ was demonstrated by XRD and fourier-transform infrared spectroscopy spectroscopy（FT-IR）.The pH-responsive release behavior of sodium molybdate and histidine in MHZ was confirmed by the UV-vis results.The MHZ-EP coating with artificial scratches（D-MHZ-EP）was immersed in a 3.5wt%Na Cl solution for 12 hours.The morphology and elemental composition of the scratch area are evaluated by scanning electron microscopy/energy dispersive spectroscopy（SEM/EDS）.The results show that there are trace amount of corrosion products at the scratch area of D-MHZ-EP,and special elements such as Mo and N could be detected,indicating that the synergistic effect of inorganic corrosion inhibitor sodium molybdate and organic corrosion inhibitor histidine endows MHZ-EP with self-healing performance.