| The smart anticorrosive coating, different from the traditional anticorrosive coating, could adjust its performance parameters after responding to the changes in the environment, and stimulate the self-healing properties so as to prevent further corrosion. The project was focused on two types of stimuli-responsive smart coatings, which were the light-responsive modified nano-TiO2coatings and the coatings with pH-responsive nanocontainers, to investigate their abilities of rapid response to the surrounding changes and the mechanism of their active corrosion protection performance for the metal substrate.A series of chromium-doped TiO2coatings were prepared by sol-gel method. The Cr-TiO2coating with homogeneous and dense structure was composed of the nanocrystalline refined to10.57nm, which contained anatase and rutile phase. Cr3+entered the lattice of anatase phase, while Cr6+was attached to the surface of TiO2nanoparticles in the form of CrO42-or Cr2O72-.The photoelectrochemical measurements indicated that chromium doping could improve the photogenerated cathodic protection performance of TiO2coating. The open circuit potential (OCP) of1%Cr-TiO2coating was230mV lower than the corrosion potential of316L stainless steel and55mV lower than that of pure TiO2coating. It was clarified that the energy level of Cr3+/Cr4+oxidizing reaction, the anatase/rutile proportion and the grain size had important effects on the photoelectric activity of Cr-TiO2coating. In the dark condition, it was demonstrated that Cr-TiO2coatings could provide active corrosion protection performances as well as excellent physical barrier properties. The SEM-EDX analysis confirmed that chromium ions could be released from the defects of the coating and form into a physical barrier in the defects so as to make Cr-TiO2coatings possess the self-healing properties.The hydrothermal method was used to prepare Cr-TiO2coatings with different doping concentration. Compared to the sol-gel method, the coating derived from the hydrothermal method became much more compact with grain refined to7.17nm.1%Cr-TiO2coating provided the best photogenerated cathodic protection performance under illumination, the OCP of which was200mV lower than the corrosion potential of316L stainless steel, but its protective effect was inferior to that of1%Cr-TiO2coating obtained from the sol-gel method. In the dark condition, Cr-TiO2coatings derived from the hydrothermal method could offer enhanced physical barrier properties compared to the sol-gel coatings and the protection efficiency of5%Cr-TiO2coating attained to99.8%; in the mean time, the low frequency impedance value of5%Cr-TiO2coating with an artificial defect on its surface exhibited no apparent decline and remained stable above1×105Ω cm2in the electrochemical impedance spectra (EIS) tests, being almost one order of magnitude higher than that of the sol-gel coating, which revealed that the chromium ions doped in the coating from hydrothermal method could offer more efficient self-healing properties.The sol-gel method was used to prepare a series of Ce-TiO2coatings by choosing environmentally friendly cerium element as doping ions. XRD and XPS measurements indicated that cerium element was concentrated on the surface of TiO2nanoparticles in the form of Ce3+and Ce4+. It was demonstrated that0.5%Ce-TiO2coating offered the best photoelectric corrosion resistance under illumination, the OCP of which was225mV lower than the corrosion potential of316L stainless steel. Its photoelectric corrosion resistance was superior to pure TiO2coating, but inferior to1%Cr-TiO2coating from sol-gel method. It was clarified that the energy level of Ce3+/Ce4+reduction reaction had an important effect on the photoelectric activity of Ce-TiO2coating. The electrochemical measurements in the dark condition indicated that on the one hand, cerium doping could improve the physical barrier properties of TiO2coating and0.5%Ce-TiO2coating offered the highest anticorrosion efficiency (96.2%); on the other hand, the interface resistance, standing for the stability of the passive film on the stainless steel, decreased from1×105Ω cm2to7×104Ω cm2in the EIS tests of the defective Ce-TiO2coating. Its decreasing amplitude was remarkably less than that of pure TiO2coating, but still greater than Cr-TiO2coating, suggesting that cerium ions could inhibit the corrosion process in the defects but their anticorrosion properties were inferior to chromium ions.Hollow mesoporous silica nanoparticles (HMSs), which were used as nanocontainers for the green corrosion inhibitor, L-Histidine, were fabricated and then uniformly distributed in the self assembled nanophase particles (SNAP) coating on Q235steel. It was indicated that per gram HMSs could be loaded with388mg L-Histidine and HMSs had pH-controlled release behaviors for L-Histidine. Within120min, the release amount of L-Histidine from HMSs in pH=10and pH=2buffer solution was3.3and2.9times higher than that in pH=7buffer solution, respectively. During48h immersion in0.5mol/L NaCl solution, the SNAP coating with pH-responsive nanocontainers exhibited excellent stability superior to the SNAP coating directly doped with corrosion inhibitors and the coating resistance remained above5×106Ω cm2. Moreover, the corrosion process could be inhibited even after the coating had been scratched on its surface. The low frequency impedance value of the coating tended to be stable (2×105Ωcm2), while that of the pure SNAP coating showed decreasing amplitude with one order of magnitude. |
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