Study On Rust Conversion Coatings Based On Gallic Acid

Steel materials with high strength,good toughness,good construction performance and other advantages,widely used in ships,oil Wells,automobiles and other fields.But there are serious corrosion problems in the use of steel materials.Organic coatings are widely used in anticorrosion because of their low cost,simple treatment method and good protection performance.However,the traditional anticorrosive coatings need to remove rust on the surface of steel before coating.Some large buildings,complex equipment and other structures in the maintenance process,due to the restrictions of construction conditions,rust removal efficiency is low,rust removal is not thorough.In this case,a kind of rust coating which can be directly constructed on a certain corroded surface and has better anti-rust effect comes into being.The most important feature of rust coating is that it can be directly coated on the metal surface that can not be thoroughly cleaned,and the obtained coating has excellent protection performance.Gallic acid can be used in the preparation of rusty coatings because it contains phenolic hydroxyl groups that can be chelated with metal ions.The carboxyl group in gallic acid can be esterified and modified into gallic acid ester.Firstly,GA-PG was synthesized from gallic acid and 1,2-propylene glycol,and coated on the treated steel plate.The rust layer became smooth and compact.The mechanism of rust transfer is that the polyphenol hydroxyl structure in GA-PG reacts with Fe2+ and Fe3+ in rust to form chelates.GA-PG treatment can improve the adhesion of rust coating and improve the anticorrosion property of the coating.The adhesion of GA-PG/varnish coating is 5.72 MPa before soaking and decreases to 2.49 MPa after soaking for 2160 h.Low-frequency impedance modulus,coating resistance and charge transfer resistance increase by an order of magnitude,while coating capacitance is always the lowest.GA-PG was added to the epoxy resin and coated on the rust removing steel plate to explore the influence of the amount of GA-PG on the rust coating system.The results show that the coating has good performance after adding GA-PG.The effects of GA-PG content on the properties of rust coating were studied.The results show that the adhesion,diffusion coefficient and corrosion resistance of coatings with 1%GA-PG content are better than other coatings.The adhesion of 1%GA-PG coating was 6.38 MPa before immersion,and decreased to 3.67 MPa after 2160 h immersion.Diffusion coefficient decreased to 1.07×10-10 cm2·s-1.The low-frequency impedance modulus is improved by two orders of magnitude,the coating resistance by three orders of magnitude,and the charge transfer resistance by two orders of magnitude.GA-TEA was synthesized from gallic acid and triethanolamine and coated on the treated steel plate.Most of the rust was transformed.GA-TEA was added to epoxy resin to explore the influence of the amount of GA-TEA on the coating system with rust.The results show that the coatings with GA-TEA addition have good performance,and the adhesion,diffusion coefficient and corrosion resistance of the coatings with 1%GA-TEA addition are better than those of other coatings.The adhesion of 1%GA-PG coating was 6.55 MPa before immersion,and decreased to 4.21 MPa after 2160 h immersion.Diffusion coefficient decreased to 0.53×10-10 cm2·s-1.Low-frequency impedance modulus,coating resistance and charge transfer resistance are improved by two orders of magnitude.