| Organic coatings account for 2/3 of the total investment in metal corrosion protection and have long been the most important means of corrosion protection.However,the passive protective coatings are easy to fail due to the inevitable defects and the permeation of aggressive species.To solve this problem,two kinds of novel coatings with active protection function were developed in this thesis,which could automatically respond to the signal of electrochemical corrosion of aluminum alloys and deliver the corrosion inhibitor to the damaged sites of the coating or corroded sites of the substrate,thus achieving the effect of self-healing to corrosion of the substrate.The key of the two self-healing coatings lies in the doped smart organic microspheres,which have the function of pH sensitivity and can release the inhibitor in directional response to the local pH change caused by corrosion on the surface of the substrate.Obviously,the preparation of the smart microspheres and the research of the pH sensitive controlled release behavior of the corrosion inhibitor are the basis for the construction of the self-healing coatings.Therefore,for the research of each smart coating system,this thesis covers three aspects:the preparation of microspheres,the research of controlled release behavior and the evaluation of corrosion protection performance of coatings.Specifically,it mainly includes the following four parts:1.We first reported a novel one-step approach for the synthesis of inhibitorencapsuling polyaniline hollow microspheres(MBT@PANI)with the pH sensitive response and controlled release function based on the supramolecular in situ interfacial polymerization technique.Then the synthesis conditions and the forming mechanism of the microspheres were analyzed and discussed.It was found that the average diameter of the synthesized MBT@PANI microspheres was 1.7 μm and the encapsulation efficiency and the loading capacity of the corrosion inhibitor MBT was above 99%and 23.5(wt.)%,respectively.Moreover,an accurate and reliable HPLC method for quantitative determination of the corrosion inhibitor MBT has been established,and the pH sensitive controlled release behavior and kinetic mechanism of MBT in 3.5(wt.)%NaCl solution were systematically investigated.The results indicated that the MBT@PANI microspheres exhibited an outstanding feature of longterm sustainable controlled release in 3.5%NaCl solutions with different pH values,and as the pH of the release medium increased,the release rate and the cumulative release amount of MBT gradually increased.With the prolonging of the release time,the release process of the inhibitor MBT had three stages and sequentially obeyed the Elovich,first-order and zero-order kinetic processes.The possible mechanism of pH sensitive controlled release was also discussed.2.The MBT@PANI microspheres were successfully incorporated with waterborne epoxy coating onto AA2024-T3 aluminium alloy substrate for the first time.The electrochemical studies have shown that the impedance modulus of the scratched MBT@PANI coating at 0.01 Hz continuously increased within 30 d of immersion in 3.5%NaCl solution,while the corrosion current density of the cathode and the anode was significantly lower than that of the control group,and the coating exhibited excellent self-healing ability.Compared with the control sample,after 70 d of salt spray test,no coating blistering or delamination was found on the scratch of the MBT@PANI coating,and no obvious corrosion was observed on the metal surface.XPS analysis clearly proved the existence of corrosion inhibitor MBT in the scratched area,which is because the local pH increase caused by the corrosion triggered the release of the corrosion inhibitor encapsulated in the microspheres.For the intact coating doped with 1(wt.)%MBT@PANI microspheres,after immersion of 180 d in 3.5%NaCl solution,the impedance modulus measured at 0.01 Hz was still one order of magnitude higher than that of the pure epoxy coating,and the salt spray test of 90 d also confirmed that the coating had an excellent long-term corrosion protection performance as expected,which could be attributed to the combined protection of polyaniline and the released corrosion inhibitor.3.Eudragit E PO microspheres encapsulated with the corrosion inhibitor 8hydroxyquinoline(8HQ)were prepared by the low-cost and easy-to-operate solvent volatilization method.Furthermore,The effects of molecular weight and the concentration of surfactant PVA,and the shear force on the particle size and morphology of 8HQ@Eu microspheres were investigated.By optimizing the experimental conditions,8HQ@Eu microspheres with an average diameter of 1.3 μm were prepared,and its corrosion inhibitor loading amount could reach 40.2(wt.)%.Moreover,a method of UV spectrophotometric for quantitative analysis of 8HQ was established,and based on this,the controlled release kinetics of 8HQ was studied.It was found that the microspheres had reliable acid-alkaline double pH sensitive function.Also,the effects of the properties of microspheres(particle size and drug loading amount)and the parameters of the dissolution medium(pH value,NaCl concentration and temperature)on the controlled release behavior were further analyzed.4.A self-healing coating was designed by introducing the 8HQ@Eu microspheres into waterborne epoxy resin as the smart filler for corrosion protection of AA2024-T3 aluminum alloy.The electrochemical study results of the scratched sample have shown that the impedance modulus(at 0.01Hz)could rebound rapidly after 12 h of immersion in the 3.5%NaCl solution and maintained continuously at one order of magnitude higher than that of the pure epoxy coating,while the corrosion current of the scratched area was suppressed to a remarkably low level within 24 h.Salt spray tests indicated that the substrate corrosion and the coating delamination near the scratched area were significantly inhibited.XPS analysis directly confirmed that the corrosion inhibitor was delivered to the corroded sites.In a word,8HQ@Eu coating had the expected excellent self-healing performance. |
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