| The chemical bonds of the anticorrosive coating are easily destroyed by high-intensity ultraviolet radiation,producing the hydroxy radicals,under the rigorous environment of the South China Sea.Therefore,the ultraviolet shielding performance of anticorrosive coating for using in this area needs to be improved.Compared with the traditional ultraviolet shielding materials,CeO2 is one of the best promising materials for ultraviolet shielding agents due to its narrow band gap,low photocatalytic activity,and cheap price.In this thesis,the CeO2 nano-powder are synthesized by precipitation method,then the ultraviolet shielding performance of the CeO2 nano-powder was improved by using doping Lanthanum.In addition,a novel type of ultraviolet shielding anticorrosive coating is proposed by combining the nano-powder with traditional aluminum-based coating,which could be effectively protected the anticorrosive coating from the serious conditions of the South China Sea.In the present work,the CeO2 nano-materials are synthesized with different temperature,time and surfactants.The result shows that the best preparation parameters are following.The precipitation temperature is 45℃,the precipitation time is 10 minutes,oleic acid is used as a surfactant,and the sintering temperature is 650℃.According to the optimal process,three different kinds of La-CeO2 were produced by doping La,and the ration of La and Ce were 5%,10%,15%,respectively.The ultraviolet shielding mechanism of the samples is studied.The semiconductor species generates the electron and hole pairs under the light conditions in the first step.And the most electrons-hole pairs will be recombined during the migration process,while some pairs could be transported to the species surface.Then the superoxide radical and hydroxy radical are quickly produced in the samples surface due to the electrons and holes have a relatively strong reduction and oxidation prosperities,respectively,indicating it will greatly damage the molecular chain of polymer of anticorrosive coating.And our results show that the anticorrosive performance of the materials could be improved by introducing the La atom,due to it can narrow the band gap of species and accelerate the recombination of electron-hole pairs.Moreover,from the(αhv)2-hv analysis,the band gap value of 5%La-CeO2(2.97 eV)is the lowest,which is 0.23 eV lower than that of pure CeO2(3.2 eV).In addition,defects(such as oxygen vacancies)in nanomaterials prevent recombination of electrons and holes.The oxygen vacancy content in La-doped CeO2 was calculated by XPS.The oxygen vacancy content of 5%La-CeO2(2.93%)is the lowest,which is about 10%lower than that of pure CeO2(3.95%),because Ce4+/Ce3+is very easy to convert in CeO2 crystals.In order to balance the negative charge excess caused by Ce3+ replacing Ce4+,some oxygen negative ions leave their equilibrium position,and migrate to outside of the crystal,and form oxygen vacancies inside the crystal to maintain electrical neutrality.To enhance the ultraviolet shielding performance,La was doped in CeO2.The formed La-Ce bond hinders the conversion between Ce4+/Ce3+,reduces the content of oxygen vacancies and defects in the crystal,and improves the electron-hole recombination rate.The novel ultraviolet shielding coating has successfully been prepared by mixing the nano-powder(5%La-CeO2)into commercial aluminum-based coating.The ultraviolet shielding performance of the novel coating on the steel substrates are investigating by UV aging test,electrochemical test,high temperature high humidity aging test and Neutral Salt Spray corrosion test.The results show that the best anticorrosive effect can be obtained when the nano-powder and the Al-based coating are mixed at a mass ratio of 20%.The coating presents the lowest self-corrosion current density(0.023 μA·cm-2)and the largest nyquist radius.In addition,the specie still can keep perfect conditions,without bubbling and cracking on the surface,after a series tests.Therefore,the composited coating not only have excellent anticorrosive properties by reflection,scattering,and adsorption ultraviolet,but also it can increase the coating’s denseness by filling the La-CeO2 nanoparticles into the pores and bubbles. |
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