Active Corrosion Protecting Painting System Based On Electrodeposited Silica Film Interlayer

Surface coating is one of the most common methods to prevent metal corrosion. The modern coating system consists of a pretreatment layer and the top coat. The former is indispensable in the whole coating system due to its temporary protective preformance and the ability to offer good adhesion to both metal surface and top coat. The traditional chrome or phosphate pretreatment layer are increasingly restricted due to serious environmental problems they caused. Although some new pretreatment technologies are environment-friendly, they have limited practical applications because of the longer process time （e.g. the rare earth salt conversion treatment）, too thin film （such as traditional sol-gel technique） or other factors limiting their practial applications. In contrast, electrodeposition sol-gel film pretreatment technology solves these problems. Compared to the passive coating system, the active one, because of its active materials, can offer corrosion inhibition even when the coating is damaged and the physical barrier properties are lost. Active protection is often achieved by adding corrosion inhibitors to different components （i.e. pretreatment, primer or top coat） in a coating system. At present, inhibitor are mainly encapsulated in the micro/nanocontainers and infiltered into the coating, however, pretreatment layer has been rarely seen to be the container of inhibitor. In this thesis, the protection mechanisms of electrodeposited silica （e-SiO₂） films were investigated. E-SiO₂ interlayer as the nanocontainer of inhibitor was proposed for active corrosion. In addition, the use of different organsilane composite modified e-SiO₂ interlayer as the pretreatment layer was also presented in the paper. The main contents are listed as follows:（1） The protection mechanisms of e-SiO₂ films were investigated. EIS and SVET were used to test temporary protection property of e-SiO₂ films with different depostied time. So that the impact of film thickness on temporary protection property can be concluded accordingly: when the e-SiO₂ film remains intact, its temporary protection property and the film thickness show a positive correlation; while the film is destroyed, its temporary protection property increases first and then declines along with the increase of the film thickness. SVET test results indicate that e-SiO₂ film made under proper deposition conditions has a certain self-healing properties. In addition, e-SiO₂ films with its highly rough and porous surface can be used to encapsulate inhibitors. Humid-heat test shows encapsulation of inhibitors improve temporary protection property of pure e-SiO₂ films.（2） Inhibitior containing e-SiO₂ interlayer for active corrosion protection. A novel painting system with promising active protection property is proposed using e-SiO₂ interlayer as the nanocontainer of inhibitors. PVP and ZnG were selected as the model inhibitors, the form inhibitor work via adsoption mechanism, and the latter protects metals by forming an impact film via precipitation in alkaline environment. SEM images show that morphology of e-SiO₂ film remains almost unchanged after loading inhibitor. EDX spectra indicate the inhibitors are evenly distributed in the interlayer of SiO₂ particles. TG and elemental analysis show the loading capacity for inhibitor of e-SiO₂ interlayer is comparable with those measured in mesoporous silica particle containers. Pull-off test shows the good adhesion of the new coating system. Both the accelerated corrosion tests on the scratched coating and the in-situ electrochemical measurements of intact sample revealed the corrosion resistance of the novel coating system has been improved significantly. The proposed novel active coating system in this paper shows slightly better anticorrosion performance than the recently-reported active protecting system containing nanoparticle containers in the bulk coatings.（3） Electrodeposited SiO₂ film post-treated with the composite organsilane for active corrosion protection. A new type of coating system based on the use of the composite organsilane （GPTMS and BTSE） modified e-SiO₂ film as the pretreatment layer was fabricated. Pull-off test indicates GPTMS acts as silane coupling agent and improves adhesion to top coat; and the accelerated corrosion tests on the scratched coating imply BTSE to provide better protection property, thereby improving the overall corrosion resistance of coating system. EIS, iron dissolution, SST and SVET tests show that GPTMS, BTSE volume ratio of 2:1 complex coating system has better corrosion protection, and SVET results also show that the system exhibits a certain self-healing properties.