Preparation And Self-healing Performance Of Ce-MOFs Based Epoxy Coating On The Surface Of Carbon Steel

Organic coatings are one of the most economical,effective and promising methods to improve the corrosion resistance of metals.However,pure organic coatings are prone to forming micropores due to the volatilization of organic solvents during the preparation process,causing metal corrosion and greatly reducing their service life.At present,adding nanocontainers loaded with corrosion inhibitors to organic coatings can endow the coatings with self-healing ability,achieve controlled release of corrosion inhibitors,and extend the protection time for carbon steels.It is significantly important for the carbon steel equipments to improve their durability.In this paper,three stimulus responsive self-healing epoxy coatings were constructed by the shell encapsulated Ce-MOFs nanocontainers loaded with green environmentally friendly corrosion inhibitors on Q235 carbon steel.The main work is as follows:The pH responsive self-healing epoxy coating（CTAP-EP）with core-shell nanocontainers（CTAP）was constructed on the surface of Q235 carbon steel.The coating was composed of tannic acid as environmentally friendly corrosion inhibitor,Ce-MOF as nanocontainers,and polyethyleneimine as shell.The encapsulation of polyethyleneimine shell is based on Schiff base reaction with quinonylated tannic acid corrosion inhibitor.The stimuli-responsive release of tannic acid from CTAP can be triggered by pH,because tannic acid corrosion inhibitor can be rapidly released from CTAP due to unstable Schiff base in relatively strong acidic environments.The low-frequency impedance mode value(|Z|_0.01Hz)of CTAP-EP maintains at 1.15×10¹⁰Ω?cm² after 35 days of immersion,which is significantly higher than pure epoxy coating（1.16×10⁶Ω?cm²）.In addition,|Z|_0.01Hz of the scratched CTAP-EP coating exhibits a process of first decreasing and then increasing four times,indicating that CTAP-EP has excellent self-healing ability.Therefore,CTAP-EP can effectively suppress further corrosion of the metal substrate and extend the service life of the coating.The pH responsive self-healing epoxy coating（CVT-EP）with core-shell nanocontainers（CVT）was constructed on the surface of Q235 carbon steel.This self-healing coating system mainly consists of vanillin as corrosion inhibitor,Ce-MOF-808 as nanocontainers,and triethanolamine as shell.The release of vanillin from CVT is greatly influenced by pH.The release amount of vanillin is highest in alkaline 3.5 wt.%Na Cl solution because the negative charge of triethanolamine shell increase first and then decrease with increase of pH,which reduce electrostatic interraction between triethanolamine shell and Ce-MOF-808nanocontainers,thereby bringing about the release of vanillin.Based on the above release mechanism,the experimental results of carbon steels immersed in extract of CVT nanocontainers show that vanillin can inhibit the corrosion of the substrate.After 63 days of immersion,|Z|_0.01Hz of CVT-EP remains 1.15×10¹⁰Ω?cm²,and no obvious corrosion is observed on the coating surface,suggesting CVT-EP can provide long-term corrosion protection for carbon steels.The self-healing efficiency of the scratched CVT-EP coating undergoes from negative to positive three times,indicating that CTAP-EP has excellent self-healing ability.The self-healing epoxy coating（CGP-EP）with controllable release was prepared on the surface of Q235 carbon steel.This coating uses glucose as corrosion inhibitors,Ce-Ui O-66with large specific surface area as nanocontainers,and hydrophilic polyethylene glycol as shell.This shell is adsorbed on the positively charged Ce-Ui O-66 surface through electrostatic interaction.As the corrosive electrolyte solution gradually penetrates into the coating,the outermost polyethylene glycol shell expands and ruptures after absorbing water,causing the release of glucose corrosion inhibitor from nanocontainers.The experimental results of carbon steels immersed in extract of CGP nanocontainers show that glucose can be adsorbed on the surface of carbon steel substrate to improve the corrosion resistance of the coating.|Z|_0.01Hz of CGP-EP still maintains 1.74×10¹⁰Ω?cm² after 35 days of immersion,and it is much higher than pure epoxy coating（7.91×10⁸Ω?cm²）,which reveals that CGP-EP has excellent corrosion resistance.In addition,the self-healing efficiency of the scratch coating of CGP-EP shows a trend of multiple decreases and then increases,which reflects the self-healing process of CGP.