Study On Anticorrosion Properties Of Inhibitor Intercalated Hydrotalcite-like Compounds/Oxide Materials For Mg Alloy Protection

Magnesium and its alloys have the advantages of low density and high strength/weight ratio and other good physical and mechanical characteristics,can be used as ideal structural materials in the light-weight engineering applications. However,the applications of magnesium alloy were limited due to their susceptible corrosion.One strategy to achieve corrosion protection is through use of a organic coating system.Due to long service life,simple technics,steady performance and other acceptable performance,organic coatings have been currently applied in corrosion resistance.A primer layer is an organic coating and it supplements corrosion protection by serving as a reservoir for corrosion inhibiting pigments.These pigment on contact with an aqueous electrolyte release inhibitor that provide active corrosion protection to defects in the coating and substrate.Conventionally chromate pigments hold the best anticorrosion efficiency and have been used widely,but they are carcinogenic.Great efforts have been made to obtain non-toxic anticorrosive pigments.Moreover,it is needed to develop the environment-friendly pigment that would provide at least the same or better corrosion inhibiting properties than chromate.In order to enhance corrosion resistance of these Mg-based materials, protective coatings were prepared on AZ31 Mg alloy and Mg-Li alloy surface by coated epoxy primer containing sheet hydyotalcites as anticorrosion pigment with excellent ion-exchange capabilities.In view of the excellent anticorrosion performance of molybdate and vanadates,the intercalation of MoO₄^2- and [V₁₀O₂₈]^6- into the interlayer of hydrotalcites were designed,and a series of inhibitor intercalated hydrotalcite-like compounds including Mg/Al-MoO₄^2-,Zn/Al-MoO₄^2-,Zn/Al-[V₁₀O₂₈]^6- were synthesized.The properties of the release of inhibitor and the ion-exchangeability with chloride ion were observed and analyzed using EDS,ICP and UV-vis.Corrosion resistance of hydrotalcites and anticorrosion performance of hydrotalcites/epoxy coatings were evaluated by polarization curves and EIS;.and the anticorrosion mechanism of these hydrotalcite materials were also presented in this dissertation.The result was demonstrated that these hydrotalcite-like compounds firstly produced released inhibitor by exchanging with aggressive Cl^- and adsorbed Cl^- which can provide appreciable corrosion resistance to Mg alloys during experiment.Nano-ZnO hold many particular performance,such as antibacterial,antiaging, shielded ultraviolet radiation,dispersion steadily and improving compactness of coating,ect,and for this reason it has been widely used in the paint industry as pigment.Based on the synthesized inhibitor intercalated hydrotalcite-like compounds,the preparation methods about in-situ created nano ZnO among Zn,Al hyrotalcite were studied in this paper.the protection performance of coating was also inverstigated.Several contributions should be mentioned in the follows:Experimental section 1.Firstly,the contrastive research of the[Mo₇O₂₄]^6- and MoO₄^2- efficiency of corrosion resistance were investigated using EDS to analyze the content of each element of the surface of Mg alloy.It is found that the efficiency of corrosion resistance of MoO₄^2- are better than that of[Mo₇O₂₄]^6-. Then,MoO₄^2- intercalated Mg/Al hydrotalcite were synthesized via one-step co-precipitation method.The ion-exchangeable and adsorptive kinetics of Mg/Al-MoO₄^2- hydrotalcite were studied.Concerning with the properties of the releasing MoO₄^2- and adsorbing Cl^-,the effective anticorrosion protection of hydrotalcites were evaluated by polarization curves and EIS.The results show that the best corrosion resitance is achieved when Mg/Al- MoO₄^2- powers are added into epoxy with 20%mass ratio;the penetrability of coating decreased as the content of the hydrotalcite increased.Experimental section 2.MoO₄^2- intercalated Zn/Al hydrotalcite were prepared which embodied double inhibitor of MoO₄^2- and Zn²⁺.The ion-exchangeability were studied using ICP,EDS,UV-vis,XRD and N₂ adsorption-desorption isotherm,and the function of corrosion resistance to the combination of the MoO₄^2- and Zn²⁺ as the double mixed inhibitor were reviewed using polarization curves and EIS.The mechanism of corrosion protection of MoO₄^2- and Zn²⁺ was discussed.The results indicate conformably that Zn/Al-MoO₄^2- hold better resistance performance than that Mg/Al-MoO₄^2-,which can improve corrosion resistance of Mg alloy due to embody MoO₄^2- and Zn²⁺ inhibitor.Experimental section 3.The intercalation of[V₁₀O₂₈]^6- into Zn/Al hydrotalcite interlayer were synthesized via one-step co-precipitation method at acidic reaction condition.TEM images show that the sheet Zn/Al-[V₁₀O₂₈]^6- has less particle size compared with Mg/Al-MoO₄^2- and Zn/Al-MoO₄^2- hydrotalcites. The ion-exchange and adsorption properties of Zn/Al-[V₁₀O₂₈]^6- were well characterized by ICP,EDS,UV-vis,XRD and N₂ adsorption-sdesorption isotherm. The excellent corrosion resistance performance of Zn/Al-[V₁₀O₂₈]^6- were revealed by electrochemical test.The mechanism of corrosion protection was proposed to be that the Cl^- ions intercalated the hydrotalcite interlayer and the released vanadate deposited on the alloy surface.Experimental section 4.Based on the synthesized Zn/Al-MoO₄^2-,nano ZnO were prepared by in-situ created among Zn/Al-MoO₄^2-.The preparation conditions were controled with the ratio between Zn²⁺and Al³⁺,reactive temperature and pH values in this paper.This work presents the comparative corrosion protection performance of the coating containing ZnO/Zn/Al-MoO₄^2- with the coatings containing nano ZnO,HT-MoO₄^2- or SrCrO₄ using polarization curves,EIS,salt spray test and uptake.Results indicate that the existence of the nano ZnO make the coating containing ZnO/Zn/Al-MoO₄^2- possess of higher corrosion resistant,barrier and active healing property.Additionally,the coating containing ZnO/Zn/Al-MoO₄^2- have longer anticorrosion protection than that of SrCrO₄.That provided the references for developing the environment-friendly and new type pigments.