Preparation And Studies Of A Class Of Layered Double Hydroxide Anti-corrosion Coatings With Super-hydrophobic And Self-healing Properties

Layered double hydroxide(LDH)nano-function material has received much attention in recent years because of its adjustable laminates composition,interlayer anionic exchangeability and amphoteric property.LDH has great application potential in many fields due to these characteristics.In this paper,the preparation method and properties of the super-hydrophobic layered double hydroxide coating with corrosion inhibitor were studied,as well as its impact on corrosion resistance of AZ31B Mg substrate.The co-precipitate and hydrothermal method were adopted to prepare corrosion inhibitor interlayered MgAl-LDH coating on the surface of AZ31B magnesium alloy.Two different kinds of corrosion inhibitors,the MoO42-and WO42-anions,was chosen and made MgAl-LDH-MoO42-/WO42-coatings successfully.The prepared coatings realized controllable release of corrosion inhibitor in the solution containing CO32-or Cl-.The self-repairing property and the excellent corrosion protective performance of the LDH coatings with corrosion inhibitor were proved by contrastive experiments of MgAl-LDH-NO3-coating.LDH has a large number of hydroxyl groups on its laminates,which result in its hydrophilic property,increasing the contact area between coatings and the corrosive medium and has an adverse effect on the anti-corrosive properties of the coating.A super-hydrophobic surface was constructed on the surface of LDH coatings to delay its water penetration time,extend its service life,and prevent the release of the corrosion inhibitor in it.As the micro-nanometer multistage structure provided the necessary conditions for super-hydrophobic surface,fluorine silane with low surface energy was grafted onto MgAl-LDH-MoO42-coating to make a super-hydrophobic surface on it.Considering the weak barrier property of nano-coatings,LDH coatings with "sandwich" structure was designed,which improved the overall thickness and the physical barrier performance of the coating,and the existence of middle layer also prevented unnecessary release of corrosion inhibitors.PVA was selected as sealing coating on the surface of MgAl-LDH-WO42-,another layer of LDH was prepared on PVA with urea hydrolysis method,which was then treated to super-hydrophobic surface.The corrosion resistance and super-hydrophobic characteristics of each layer of the above coating were characterized.The morphology,structure and corrosion behavior of the LDH were characterized by X-ray diffraction(XRD),scanning electron microscope(SEM),Fourier infrared spectrometer(FT-IR),and other means.The degree of corrosion on the coating in 3.5wt%NaCl was recorded with optical images.The corrosion resistance of coatings was characterized by electrochemical impedance spectroscopy(EIS)and polarization curves.The release of LDH with corrosion inhibitor in the corrosive medium was monitored by inductively coupled plasma atomic emission spectrometry(ICP-AES).The contact angle(CA)of coatings were measured to estimate their hydrophobic performance.Results show that LDH coatings with corrosion inhibitors improved the corrosion resistance of magnesium alloys obviously,and each super-hydrophobic surface produced in this paper had static water contact Angle above 153°,and superior corrosion resistance was detected than coating before the hydrophobic modification.