Study On The Anti-corrosion Performance Of Waterborne Epoxy Coating Modified With Functionalized Boron Nitride Nanosheet

Coating is one of the most effective methods for metal corrosion protection.However,traditional organic solvent-based coatings can release volatile organic compounds(VOCs)during actual service,harming the environment and human health.So,the development of environmentally friendly and green water-based epoxy coatings is a trend in the field of corrosion protection coatings.However,during the curing process of water-based coatings,water evaporation forms inherent defects such as micropores and cracks,which significantly affect the corrosion protection ability of the coatings.Therefore,to address the problem of poor long-term corrosion protection ability of water-based epoxy coatings.This project designed three composite functional fillers with combined"active-passive"dual protection functions based on two-dimensional nanomaterial boron nitride nanosheets(BNNS),which significantly enhanced the long-term corrosion resistance of water-based epoxy coatings.(1)The traditional corrosion inhibitor 2-amino-5-mercapto-1,3,4-thiadiazole(ATT)was used as intercalator to obtain ATT/BNNS by the modification and stripping of boron nitride by liquid phase assisted ultrasound.The results of FTIR,XPS and TEM showed that ATT was successfully grafted on BNNS by Lewis acid-base process,which fully stripped the boron nitride and prevented the BNNS from reaggregation and stacking.Then BNNS,ATT and ATT/BNNS were used as fillers to disperse evenly in the waterborne epoxy coatings,and the corresponding waterborne epoxy composite coatings were obtained by spraying on the copper electrode.The surface morphologies and wetting state of the different coating systems were compared using AFM and contact angle testing.Electrochemical impedance spectra(EIS)and corresponding fitting results,as well as optical surface morphologies after long-term immersion,indicated that the WEP ATT/BNNS coating had the best long-term corrosion protection ability,and the excellent corrosion resistance of the composite coating was due to the combined passive protection of BNNS and active protection of ATT.(2)Functional carbon point corrosion inhibitors(FCDs)based on glucose were designed and prepared,and FCDs was used as intercalator to strip and modify boron nitride.Thus,FCDs/BNNS composites were obtained.SEM,TEM,FTIR,and XRD techniques were used to characterize the microstructure and composition of FCDs/BNNS.A certain ratio of FCDs,BNNS,and FCDs/BNNS functional fillers was added to a water-based epoxy paint,and the corresponding coatings were prepared on copper alloy surfaces by spraying.The corrosion protection performance of the WEP FCDs/BNNS coating was the best among the four coatings,as shown by EIS,Local electrochemical impedance spectra(LEIS),and optical surface morphology results.After immersion in a 3.5 wt%Na Cl solution for 40 days,the fitted total impedance value of the WEP FCDs/BNNS coating(4.97×10~5Ωcm~2)was still one order of magnitude higher than that of the pure WEP coating(3.36×10~4Ωcm~2).The synergistic mechanism of FCDs/BNNS nanocomplex is:On the one hand,BNNS acted as a physical barrier to prolong the diffusion path of corrosive media,filled the inherent defects of coating,and slowed down the corrosion process of metal.On the other hand,FCDs not only improved the dispersion and compatibility of BNNS in the coating as an intercalator,but also acted as a corrosion inhibitor to adsorb on the substrate surface of the damaged area of the coating to inhibit the development of corrosion.(3)ZIF-7 and BNNS complex(NZ/BNNS)loaded with 5-aminotetrazole was synthesized by solvothermal method using zinc gluconate as zinc source,benzimidazole as ligand and BNNS stripped.The structure and composition of ZIF-7,NZ and NZ/BNNS were characterized by FTIR,XRD,TEM,XPS and SEM.BNNS,NZ and NZ/BNNS were added to the water-based epoxy coating and sprayed on Q235 carbon steel electrode to prepare the corresponding WEP composite coating.The results of the experiments on EIS,potentiodynamic polarization(PDP)and scratch test showed that the impedance modulus of WEP NZ/BNNS at the frequency of 0.01Hz was about 1～1.5 orders of magnitude higher than that of WEP coating during the soaking cycle,and the anti-corrosion efficiency reached98%,and almost no corrosion products were observed on the surface of the sample.For WEP NZ/BNNS coating,in addition to the passive protection of BNNS as a physical barrier,NZ,as a smart nanocontainer loaded with corrosion inhibitors,degraded in response to p H stimulation under the local acidic conditions caused by corrosion construction of carbon steel.The 5-ATZ inhibitor coated internally and the Zn G inhibitor anchored on the surface are released and adsorbed on the corroded or exposed carbon steel surface to form a dense protective film,providing active protection for the metal.