Preparation And Performance Study Of Silica-Based Superhydrophobic Surface Composite Coatings

Superhydrophobic surfaces have attracted extensive research due to their unique non-wetting properties and have shown good prospects for application in areas such as self-cleaning,corrosion prevention and resistance reduction.However,the weak surface stability,poor durability,complex preparation process and high cost of superhydrophobic coatings are currently limiting their practical applications.Highly efficient and durable coatings with multi-functional corrosion protection are the hotspot research topics in recent years.Aiming to improve the stability and durability of superhydrophobic coatings,this thesis reports the development of two types of superhydrophobic coatings based on sol-gel technology,and the investigation of corrosion resistance,stability and durability performance of the sample coatings as well as the related protection mechanisms.The main work and findings are as follows.（1）A silicon based/zirconium oxide（SG-M/ZrO₂）composite coating was prepared by the sol-gel method using carbon steel 201 as the substrate.The results show that when the SG-M/ZrO₂ mass mixing ratio is 8:1,the prepared SiO₂-ZrO₂ composite coating has a more uniform surface,good film formation and no defects,and has the best corrosion resistance.The appropriate amount of ZrO₂ can effectively improve the mechanical properties of the coating,the pencil hardness of the coating can reach above 7H,and the cross-hatched adhesion test shows that the bond strength of the coating can reach grade 0.Electrochemical results show that the appropriate amount of ZrO₂ in the SiO₂ matrix is beneficial to enhance the mechanical properties and corrosion resistance of the coating.When the SG-M/ZrO₂ composite coating thickness is25μm,the coating has the best corrosion resistance.（2）In order to further increase the corrosion resistance and improve the stability of the coating,coatings with different contents of Ce³⁺corrosion inhibitor were prepared on the basis of the above coating formulation.A corrosion inhibitor with a content of 0.91 wt%(0.2Ce³⁺-B-2 coating)can effectively retard the corrosion of the metal substrate,which is mainly due to the cathodic protection of Ce³⁺ions by releasing the corrosion inhibitor on the surface of the damaged substrate.This is because Ce³⁺ions have a greater negative potential than Fe³⁺ions.F-SiO₂@SG-M/ZrO₂/Ce³⁺superhydrophobic coatings were prepared by introducing fluorinated silica（F-SiO₂）,resulting in a water contact angle greater than 150°and a rolling angle of less than 10°.The EIS results showed that the superhydrophobic coatings had better corrosion resistance.After 720 hours of salt spray testing,no signs of corrosion or cracks were observed,and the contact angle of the F-SiO₂@SG-M/ZrO₂/Ce³⁺superhydrophobic coating remained above 150°after 30 hours of drop impact testing,10 friction cycles,12 days of simulated seawater exposure and 50 days of outdoor exposure,indicating that the F-SiO₂@SG-M/ZrO₂/Ce³⁺superhydrophobic coating had excellent stability and durability.（3）A two-step process was developed,which consisted a base-coat prepared by a electrochemically assisted deposition（EAD）process and a superhydrophobic top-coat by dip coating process.The base layer（E-MTES）was prepared by electrochemically assisted deposition using methyltriethoxysilane（MTES）as a precursor to the sol-gel solution.The surface was then modified using 1H,1H,2H,2H-perfluorooctyltriethoxysilane（PFOTS）to obtain a superhydrophobic E-MTES/PFOTS coating.The surface topography,thickness and surface roughness of the E-MTES coating can be adjusted for different deposition times and deposition potentials.The E-MTES/PFOTS coating has a maximum water contact angle of 153°and a rolling angle of less than 10°.The layered surface topography of the silica-based coating ensures that the low surface energy PFOTS topcoat is chemically bonded to the base paint and provides superhydrophobic property.The superhydrophobic surface has excellent self-cleaning properties and can effectively remove surface contaminants under the action of water droplets.The superhydrophobic E-MTES/PFOTS coating has high chemical stability in aggressive solutions（acids and bases）;in addition,it demonstrates good wear resistance and can withstand 10 friction cycles of sandpaper abrasion and still maintain a WCA of 150°and a rolling angle of less than10°.The developed two-layer coating system allows for a high strength homogeneous coating on complex substrates,using a simple PFOTS dip coating on the base layer with chemical bond to the base layer.This method provides an environmentally friendly and widely used method for the preparation of sol-gel silica-based superhydrophobic surfaces for enhanced surface protection of metal substrates.