| Most of the hot-dip galvanized steel(HDG)has a short service life due to insufficient coating thickness,and broken coating during construction or transportation,which often needs to be recoated with the cold galvanizing coating(CGC)to enhance the anti-corrosion effect.However,the weak adhesion and the poor corrosion resistance of the coating on HDG make it difficult to ensure the long-term and stable service of HDG substrates and prevent large-scale application.Therefore,this dissertation focuses on the enhancement technology of the CGC/HDG substrate interface and the inhibition of self-corrosion of zinc powder inside CGC,designs a series new of CGC and investigates the enhancement mechanism of its corrosion protection performance,which provides a new solution for the service and performance enhancement of CGC on HDG substrate.Firstly,the interfacial interaction between CGC and HDG is enhanced by the pretreatment layer of polydopamine(PDA)and the addition of silane coupling agent,and both of them achieve the simultaneous enhancement of coating adhesion and corrosion resistance through the formation of cross-linked network and barrier layer.Second,a pH-responsive material(PB@ZnO)for CGC primer was designed to achieve the suppression of self-corrosion of zinc powder inside the coating.This material can intelligently release PDA/BTA to inhibit the corrosion of zinc powder when the pH inside the coating changes,prolonging the service life of CGC and enhancing the self-healing ability of CGC itself.Finally,we modulate the functional group structure of PB@ZnO material to investigate its pH response behavior and its effect on the corrosion resistance of CGC,which provides an optimal solution for the enhancement of PB@ZnO in CGC protection performance.This dissertation consists of four main parts as follows:(1)PDA pretreatment layer is constructed on the surface of the HDG substrate by solution polymerization and subsequently coated with CGC for corrosion protection of HDG.The results of water contact angle,Fourier infrared spectroscopy(FTIR)and Xray photoelectron spectroscopy(XPS)confirm the high surface free energy and secondary grafting reaction capability of HDG substrates.Adhesion tests showed that the coating with the pretreatment layer(PDA-1/CGC)exhibited a lower adhesion loss(28.7%)and a better interfacial adhesion profile than the control sample(CGC).The results of electrochemical and salt spray tests show that PDA-1/CGC has excellent corrosion resistance,and the XPS analysis shows that the improvement of corrosion resistance is achieved by the synergistic effect of the PDA layer and PDA-Zn2+chelate product at the interface,which gives PDA-1/CGC good adhesion performance and long-lasting corrosion resistance.(2)Two CGCs with different silane coupling agents were directly used for corrosion protection of HDG,and the mechanism of different silane actions in CGCs was elucidated by XPS analysis and IR characterization.The coatings with silane coupling agents showed good adhesion and lower adhesion loss(21.4%)due to the formation of a cross-linked network inside the coating and the bonding at the coating/substrate interface.Electrochemical tests showed that the coating with chloropropyltriethoxysilane(CPTES/CGC)still had cathodic protection after immersion in 3.5 wt.%NaCl solution for 2500 h.Polarization tests showed that the corrosion current density(1.55 ×10-6 A/cm2)was one order of magnitude lower than that of CGC(8.59×10-5 A/cm2).The observation of corrosion morphology after immersion experiments also showed that the corrosion degree of CPTES/CGC was lower than that of CGC.the cross-linked network and the interfacial effect gave the coating good interfacial properties and corrosion protection.(3)A pH-sensitive controlled release material(PB@ZnO)loaded with PDA and corrosion inhibitor(BTA)on the surface of ZnO nanoparticles was successfully prepared in the water/ethanol system.The pH-sensitive response of PB@ZnO material(BTA loading of 6.07%)was verified by zeta potential and UV spectrophotometry.The release and effective effect of PDA/BTA in PB@ZnO material were verified by electrochemical test on hot-dip galvanized substrate(inhibition efficiency of 64.02%)with zinc powder immersion experiment(no sign of corrosion after 4 h immersion).After adding PB@ZnO into CGC for HDG corrosion protection,electrochemical tests of the complete coating showed excellent corrosion resistance,and the corrosion current density of PB@ZnO/CGC decreased by two orders of magnitude compared to CGC,reaching 4.38×10-7 A/cm2.electrochemical tests of the scratch coating and salt spray tests showed that the PDA/BTA in PB@ZnO.The combination of shielding effect,selfhealing effect and intelligent inhibition of PB@ZnO material in CGC has optimized the corrosion protection performance and self-healing ability of CGC itself.(4)Based on the modulation of PDA functional group content,the PB@ZnO materials(PB@ZnO-1,PB@ZnO-3 and PB@ZnO-5)thus exhibit different pHsensitive behaviors,while the loading rates of PDA and BTA are increased to a maximum of 53.63%and 9.15%,respectively.)exhibited significantly better corrosion protection than CGC,and the electrochemical results showed that the reaction impedance value of PB@ZnO-1/CGC for zinc powder was improved by two orders of magnitude compared with CGC.In addition,PB@ZnO-1 showed its excellent selfhealing ability in the scratched coating,and the suppression of self-corrosion of zinc powder inside the coating and the repair of defects at the scratch were mainly achieved by the PDA/BTA released from the PB@ZnO material.In conclusion,the pH-sensitive behavior of PB@ZnO material was successfully modulated and applied to CGC,which effectively enhanced the self-healing ability and corrosion resistance of the coating. |
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