Preparation And Properties Of Epoxy Coating Modified By Metal-phenolic Network

Ships,channel bridges and tunnels served in marine environment are often subjected to severe corrosion,causing huge economic loss.One of the most effective anticorrosion strategies is coating technology.However,organic coating is often porous,and corrosive media such as oxygen,water and chloride ion can easily penetrate into the interior of the coating through these pores.Therefore,in order to improve the corrosion resistance of organic coating in UV and salt spray environment,it is necessary to modify the coatings with different additives or pigment.Among them,nano filler is one of the most effective methods.In addition,the local corrosion of metal beneath coating is difficult to detect.Before Visible to naked eyes,underlying corrosion may have become very severe.Therefore,an early corrosion detection for coating faults would be very valuable for practical applications.In this paper,modified epoxy coating was firstly brushed on the surface of AA7075-T6aluminum alloy and then subjected to two typical aging tests,salt spray(SST)and ultraviolet(UVA).The modification effects of nanoparticles on adhesion,corrosion resistance and durability of the coating were studied.In addition,a kind of"intelligent coating"with self-sensing ability was prepared,aiming to detect corrosion defects underlying coating.The main contents are as follows:(1)Metal polyphenol networks(MPN)were prepared by coordination of tannic acid(TA)with Ce³⁺and Eu³⁺,which were in situ grown on the surface of carbon nanotubes(CNTs)and polymethyl methacrylate(PMMA)microspheres respectively to prepare Ce³⁺-TA-CNTs and Eu-TTA-TA@PMMA nanoparticles.By Fourier transform infrared spectroscopy(FTIR),Raman spectroscopy(Raman),X-ray photoelectron spectroscopy(XPS),ultraviolet-visible spectrophotometer(UV-Vis)and fluorescence spectrophotometer,scanning electron microscope(SEM),transmission electron microscopy(TEM)and X-ray energy dispersive spectrometer(EDS),and the characterization of structure of nanoparticles,the results show that the Ce³⁺in Ce³⁺-TA-CNTs nanoparticles state and phenolic hydroxyl oxygen through the coordination of TA formed metal nanomaterials polyphenols network.TEM and EDS results showed that CNTs were successfully grafted with Ce³⁺and tannic acid chelates.In addition,the results of FTIR,XPS,UV-Vis and fluorescence photometer showed that Eu-TTA-TA was successfully in-situ grown on PMMA microspheres,and obtained Eu-TTA-TA@PMMA nanoparticles exhibited varying fluorescence intensity with different p H.p H=3,the weakest fluorescence intensity,p H=9,the strongest fluorescence intensity.(2)The effects of CNTs and Ce³⁺-TA-CNTs nanoparticles on the corrosion resistance and durability of epoxy resin(EP)coating were studied.Using adhesive force tester,differential scanning calorimetry(DSC)to determine the performance before and after aging.Electrochemical impedance spectroscopy(EIS)change of different cycles was investigated,compared with the unmodified EP coating,adhesive force of EP composite coating with Ce³⁺-TA-CNTs modified at least increased 2.5 MPa,and exceeded 4 MPa after aging.It can be seen that Ce³⁺-TA-CNTs could improve the adhesion of EP coating.Besides,|Z|_0.01Hz of pure EP coating after five aging cycles dropped to below 10⁶?·cm².The|Z|_0.01Hzof composite coating after eight aging cycles was higher than 10⁶?·cm².It's illustrated that the Ce³⁺-TA-CNTs nanoparticles could improve corrosion resistance and durability of EP coating.(3)The response ability of Eu-TTA-TA@PMMA and Ce³⁺-TA-CNTs/Eu-TTA-TA@PMMA nanoparticles to the corrosion resistance and coating defects of EP coating was studied.The results showed that glass transition temperature(T_g)of Eu-TTA-TA@PMMA/EP composite coating decreased to 44.69?,and the adhesion strength increased by 45%and 138%.respectively,compared with pure EP coating after aging.EIS tests showed that|Z|_0.01Hz of Eu-TTA-TA@PMMA/EP composite coating after 5 cycles aging was still higher than 10⁷?·cm².In addition,compared to the Eu-TTA-TA@PMMA/EP,|Z|_0.01Hz of Ce³⁺-TA-CNTs and Eu-TTA-TA@PMMA nanoparticle modified coating,was higher than10⁸?·cm² after five aging cycles.Adhesive force,compared with pure EP,increased by 79%and 178%before and after aging,respectively.Furthermore,with salt spray test increasing,more pores and micro-cracks would occur on Eu-TTA-TA@PMMA/EP coating,corrosive electrolyte could reach aluminum alloy matrix,which cause fluorescence attenuation.Therefore,the signal of coating defects could be characterized by fluorescence intensity.Based on fluorescence response,it would be promising for early visual inspection of coating defects.