Research On PH-responsive Self-healing Anticorrosive Coating Based On Metal Organic Framework Materials

Based on the development of traditional "passive" barrier coatings,a self-healing anti-corrosion system can sense the changes of external corrosion micro-environment and "actively" repair the surface of coatings.It is prepared by adding the environment-responsive micro/nano materials into the existing physical barrier coatings,which releases the inhibitors to delay metal corrosion and prolong the service life of metal materials.In practical industrial applications,environmental responsive micro/nano materials hinder the development of extrinsic self-healing anticorrosive systems due to low corrosion inhibitor loading,easy loss,difficulty in large-scale production and poor compatibility with coatings.Zeolite imidazole framework(ZIF)is an emerging class of organic-inorganic hybrid porous functional material,which belongs to a category of metal organic framework(MOF).Due to well-developed pore structure,the large surface area,superior design flexibility,simple synthesis process and so on,ZIF has become a research focus in the field of nanoporous materials.In this paper,the extrinsic self-healing anti-corrosion system is based on the synthesis of pH-responsive ZIF nanomaterials with different compositions,particle sizes and morphologies.We investigated the self-healing performance of ZIF nanomaterials in acidic environment,and discussed the influence factors and mechanisms of self-healing process.The main research contents are as follows:Firstly,ZIF-7 nanoparticles,such as 60 nm spherical,400 nm spherical,325 nm rhombohedral dodecahedron and 1500 nm rod,were prepared by water(solvent)thermal method,which is by means of adjusting the experimental parameters such as solvent type,concentration of metal ions and corrosion inhibitors and reaction temperature.Scanning electron microscopy,powder X-ray diffraction and thermogravimetric were used to systematically study surface morphology,crystal structure and the content of corrosion inhibitor.The results show that the crystal structure of ZIF-7 nanoparticles have nothing to particle size and morphology,and the theoretical content of inhibitor reaches to 65%.Due to the high corrosion inhibitor content and pH-responsive property,ZIF-7 nanoparticles were chosen as active components to modify the organic coating,which impart the acidic feedback function to the traditional coating,and fully release the corrosion inhibitor in the damaged area to form a stable protective film,thereby preventing the corrosion reaction from spreading and achieving excellent self-healing corrosion protection.Secondly,ZIF-7@BTA nanoparticles with different molar ratios of ligands were prepared by post-synthesis substitution strategy at room temperature.The surface morphology,crystal structure,ligand ratio and pH-responsiveness of ZIF-7@BTA nanoparticles were systematically analyzed by means of 1H nuclear magnetic resonance spectroscopy,high performance liquid chromatography and other characterization methods.The results indicate that ZIF-7@BTA nanoparticles containing about 30 wt%benzotriazole(BTA)can provide 99.4%inhibition efficiency to Q235 carbon steel under acidic conditions.While under neutral conditions,only less than 4 wt%of BTA is leached out,effectively avoiding the premature loss of corrosion inhibitors.In addition,when ZIF-7@BTA nanoparticles are uniformly dispersed in the epoxy coating,the adhesion between the coating and the metal substrate is exactly enhanced,and it is proved by electrochemical impedance spectroscopy and optical microscopy that the novel coating system has a good self-healing corrosion resistance.