Preparation Of Highly Dispered Montmorillonite/Silica Dispersion And Its Application In Waterborne Epoxy Coatings

Surface coating technology is one of the most effective methods of protecting steel;however,structural steel corrosion is still a common problem up to now.Waterborne epoxy coatings possess low VOC emissions,outstanding chemical resistance and good adhesion to steel substrate and have been gained more and more attention and extensive research in corrosion protection field.However,waterborne epoxy coatings commonly contain a lot of hydrophilic groups which easily form a path for water in coating,then for other corrosive agents,so as to weaken the corrosion protection of coatings and limit its application in the corrosion protection of steel structures.At present,the anti-corrosion properties of waterborne epoxy coatings are mainly improved by adding some layered materials such as montmorillonite and graphene.However,unmodified materials are difficult to be directly incorporated into waterborne epoxy coatings and may reduce their barrier properties.Therefore,it is urgent to develop a material with low-cost,high barrier,easy usage to modify the corrosion resistance of waterborne epoxy coatings for promoting "oil to water" in the industry.In this paper,the aqueous montmorillonite dispersion MC with a solid content of8% was prepared by green one-step surface modification of layered montmorillonite(MMT)with barrier property under ultrasonic action and high-speed dispersion conditions,using the amphiphilic surfactant cetyltrimethylammonium bromide(CTAB)as the modifier,and its stability,dispersibility and microstructure were tested.Thermogravimetric analysis(TGA),infrared spectroscopy(FT-IR)and X-diffractometer(XRD)studies revealed that the modifier CTAB was inserted into the montmorillonite layer;Ultraviolet transmission spectroscopy,Zeta potential analyzer and transmission electron microscopy(TEM)characterization showed that MC had good dispersion,good fluidity,and no precipitation for more than 3 months.The anticorrosive waterborne coatings WEP-MC wasobtained by mixingthe best MC dispersion and waterborne epoxy coatings,and the testings of two parts have been done.Firstly,the water resistance and alkali resistance of WEP-MC were tested.The results show that the modified water-based anti-corrosion coating has good water resistance and alkali resistance owing to dispersed montmorillonite lamella,which can form a physical shielding layer in matrix to block the penetration of corrosive media such as water,oxygen and salt ions.Secondly,the anticorrosiveperformance of the modified WEP-MC was mainly studied by using electrochemical and neutral salt spray.The analysis of electrochemical impedance spectroscopy shows that the corrosion resistance of the modified coating WEP-MC-0.4 mixed with 0.4wt% MC dispersion reaches the best.The fitting results of Tafel curve reveals that the corrosion current density is the smallest.After 300 h of salt spray test,the anti-corrosion of the WEP-MC-0.4 coating is the best,indicating that the WEP-MC-0.4 coating has the best corrosion resistance.Then,a green physical modified water-based nano-silica dispersion NS(10%)-2h with 10% solid content was successfully prepared by regulating the ultrasonic time and solid content of nano-silica with corrosion resistant performance dispersed in water by using ultrasonic technology.The stability,dispersibility and microstructure of nano-silica dispersion NS(10%)-2h was tested and characterized.Results obtained from ultraviolet transmission spectroscopy,zeta potential analyzer and high-resolution scanning electron microscopy(SEM)shows that NS(10%)-2h has a high degree of dispersion,and no sedimentation is observed more than 3 months.Finally,MC and NS(10%)-2h dispersion were used together to construct a new "surface-point" barrier network in waterborne epoxy coatings.The results show that the corrosion resistance of waterborne epoxy coatings mixed with 0.4wt% MC and 0.1wt% NS(10%)-2h is the best.