Synthesis And Characteration Of Anti-corrosion Self-healing Coatings Based On Nanocontainers

Metal corrosion causes great economic losses and environmental problems.One of the most common methods for protecting a metal surface from corrosion against a harsh corrosive environment involves the application of an organic polymer coating.The protection mechanism of a polymer coating consists of the polymer serving as a barrier to inhibit corrosive species from contacting the metallic surface.However,if this barrier is partially damaged,the coating itself cannot stop corrosion propagation,and the coating will lose its protective function due to water and oxygen diffusion to the metal/coating interface.Corrosion inhibitors can be incorporated into a coating system to enable a self-healing effect that ensures prolonged protection even in the presence of coating damage.However,the direct addition of these inhibitors into the coating can lead to undesirable effects,such as the uncontrolled release of the corrosion inhibitors,degradation of the coating and loss of inhibition capability.Recently,many researchers have studied the development of self-healing protective coatings using nanocontainers to load corrosion inhibitors.Many templates,including porous and mesoporous metal oxide particles,layered double hydroxides?LDHs?,and halloysite nanotubes,have been utilized for the encapsulation of corrosion inhibitors.The most important factor in the design of inhibitor-loaded carriers is developing containers sensitive to the surrounding environment,such as local pH changes,temperature changes,light and mechanical pressure.Corrosion process is typically characterized by anodic dissolution and cathodic oxygen reduction.With the onset of corrosion,pH decreases in the micro-anodic zones due to the metal dissolution and subsequent hydrolysis reactions,while oxygen reduction reaction leads to the pH increase in the micro-cathodic zones as a result of the hydroxide ions formation.In response to a local environmental change,a change of pH is a more preferable trigger for corrosion protection.Therefore,utilizing pH shift around corrosive microzones as a trigger for corrosion inhibitors release is one of the most promising approach to develop self-healing coatings.In this study,the nanocontainers loaded with corrosion inhibitors and polyaniline-modified TiO₂ particles had been designed and fabricated.The modified particles were dispersed in water-based epoxy coatings for protection of carbon steel.The thesis is divided into five sections,which are summarized as following:1.Urchin-like mesoporous TiO₂ hollow spheres were adopted as carriers for the encapsulation of benzotriazole?BTA?.The inhibitor-loaded TiO₂ containers were modified by polyelectrolyte shells using layer-by-layer?LbL?self-assembly technology.The release behavior of the encapsulated inhibitor was investigated using UV-visible spectroscopy.Corrosion protection performance of the epoxy coating with polyelectrolyte-modi fied TiO₂ containers was studied using electrochemical impedance spectroscopy?EIS?and a scanning Kelvin probe?SKP?.Epoxy coating with the polyelectrolyte-modified TiO₂ containers provided better barrier properties than that of the epoxy,epoxy/BTA,and epoxy/TiO₂ coatings.From the SKP results,the coating containing polyelectrolyte-modified TiO₂ containers exhibited a self-healing capability relative to that of the blank coating.2.The as-prepared mesoporous hollow TiO₂ was used as carrier to load the corrosion inhibitor 2-mercaptobenzimidazole?MBI?.The outer shell of inhibitor-loaded containers was modified by a SiO₂ film,which was obtained from hydrolysis of tetraethyl orthosilicate?TEOS?and?3-aminopropyl?triethoxysilane?APTES?.The structure of the TiO₂ containers was studied using X-ray diffraction?XRD?analysis,field emission scanning electron microscopy?FESEM?,and Fourier transform infrared?FTIR?spectrometry.The release behavior of the corrosion inhibitor was investigated using UV-visible spectroscopy.The release rate of MBI in water medium was pH 2>pH 4>pH 7.EIS results showed that incorporation of modified TiO₂ containers had positive influence on corrosion resistance of the film.After 168 h of immersion,the impedance values of the coating with modified TiO₂ still retained two orders of magnitude relative to that of the blank coating.Polarization measurements showed that carbon steel immersed in NaCl solution in the presence of TiO₂/MBI/SiO₂ particles had the highest inhibition efficiency at pH 2.In comparison with the blank coating,results obtained from SKP measurements confirmed active corrosion protection performance of the modified TiO₂ containers.3.TiO₂/PANI particles were synthesized by in situ polymerization and dispersed into a water-based epoxy coating.The structure and morphology of as-prepared TiO₂/PANI particles were characterized by FTIR,XRD,and SEM.The anticorrosion performance of the coating was studied by electrochemical impedance spectroscopy?EIS?and scanning electrochemical microscopy?SECM?.EIS analysis showed improved corrosion protection properties in the presence of TiO₂/PNAI particles.SECM measurements were performed to monitor the reduction of oxygen process as a function of exposure time in 3.5 wt%NaCl solution.SECM results showed that the epoxy coating with TiO₂/PANI particles had a self-healing performance relative to the blank coating after artificial defect exposure to the corrosive environment.4.Water-based epoxy coating containing CeO₂ nanocontainers was successfully applied on carbon steel for corrosion protection.CeO₂ nanocontainers were loaded with the corrosion inhibitor benzotriazole?BTA?.Polyelectrolyte multilayers were deposited on the loaded nanocontainers by layer-by-layer assembly method.Responsive release of BTA molecules were studied in water media at different pH values using UV-visible spectroscopy.The release rate of BTA in water medium was alkaline>acidic>neutral.The release speed of corrosion inhibitor in alkaline solution is fast at early stage.Approximately 35 wt%of MBI was released within 1 h and 92 wt%of MBI was released within 24 h.The anticorrosive performance of the epoxy coatings doped with modified CeO₂ was tested by immersion of the coated carbon steel in 0.5 M NaCl solution.Electrochemical impedance spectroscopy?EIS?was used to estimate the influence of smart nanocontainers on the passive corrosion resistance.The self-healing performance of the coating with modified CeO₂ nanocontainers was studied by scanning Kelvin probe?SKP?.From results of EIS and SKP,the addition of pH-sensitive nanocontainers into the epoxy resin inhibited the corrosion activities on the metal surface.5.An intelligent coating containing pH-responsive attapulgite?ATP?nanocontainers was successfully prepared.The corrosion protection performance of the water-based coating was studied.These nanocontainers were assembled with polyelectrolytes and inhibitors by using a layer-by-layer?LBL?self-assembly technology.The release behavior of encapsulated inhibitors was investigated through UV-visible spectroscopy.The release speed of BTA in alkaline solution is the fastest among all the conditions.The release curves display a quick release region at pH 10 and approximately 80 wt%of BTA was released within 24 h.The assembled ATP has good dispersion in epoxy coatings.The surface morphology of the coatings is wrinkled,which increases the contact angle of the coatings and reduces the coating hydrophilicity.The corrosion behavior of the coating was tested with electrochemical impedance spectroscopy?EIS?and scanning electrochemical microscopy?SECM?.Corrosion results from EIS showed that the incorporation of the assembled ATP nanoparticles into the epoxy matrix improved the barrier properties of the coating,three orders of magnitude relative to that of the blank coating after 384 h immersion.SECM measurements performed on scratched samples revealed that the addition of the assembled ATP nanoparticles to epoxy coating exhibited a self-healing capability for carbon steel protection.