Study On Corroion Process And Mechanism At The Interface Of Waterborne Arcylic Coating/Steel

In this paper, physical properties, chemical properties and electrochemical parameters change in the process of the corrosion failuresfor waterborne acrylic coatings with different coating/metal interfaces have been analyzed. The mechanism of multiple factors (resin structure, defect type, ion concentration) on the corrosion process of coating/metal interface has been determined. And a new type of high performance coating has been developedStructural characteristics and failure process of different types of water-borne acrylic coatings were analyzed byelectrochemical impedance spectroscopy and chemical analyses. The results showed that the conventional acrylic coating had a good barrier performance, but corrosionoccurred quickly when the corrosive medium penetrated into the coating/metal interface. Ternary copolymer coating was hydrophilic and its shielding performance was weak. But because of the stable COOFe bonding between resin and metal, the corrosion coating/metal interface reaction could be slower down. As a result, ternary copolymer coating showed a better corrosion resistance.Cathodicdisbonding failure process of water-borne acrylic coatings was acceleratedby using artificial defects, and evolution process of wet adhesionof the coating was tested. Results showed that the adhesionofconventional acrylic coating and metal substrate was mainly physical adsorption.Wet adhesion was weak and was reducedwith the corrosive medium diffusion to the coating/metal interface, leading to rapid corrosion at the interface. Ternary copolymerization coating and metal was primarily chemically bonded, showing good wet adhesion;the extent of delamination was lowest amongthree kinds of coatings. Corrosion reaction occurred preferably under the scratch defect, and process of water absorption inintact coating was given priority underpore defect.The influence of ionic concentration and pH to coating delaminationprocesswere studied by using EIS and LEIS. The results showed that delamination of conventional acrylic and ternary copolymer coatingwas accelerated with higher ionic concentration.The delamination rate of conventional acrylic coating increased with the ion concentration. In comparison, the ternary copolymer coating demonstrated a smaller delamination degree at various concentrations. From pH=4to13, the ternary copolymer coating showed a good ability to resist disbonding.Zinc phosphate was used to modify the common water-borne acrylic coating. The results show that zinc phosphate can be dissolved in corrosive medium and react with iron formed a stable and protective zinc phosphate iron, etc, which can inhibit anode corrosion process. Meanwhile, because of chemical activation the zinc phosphate which can produce protective films containing carboxyl and hydroxylthe wet coating adhesioncan be enhanced. This is expected to prevent the corrosive medium from lateral diffusion at coating/metal interface and slower down thedisbonding.Carbon nanotubes was used to modify conventional acrylic coating, results show that because of the nano size effect, it can effectively improve coating’s shielding performance. Dispersedevenlyon the coating/metal interface,carbon nanotubes enhanced the adhesion between coating and metal substrate, thereby inhibiting the corrosion reactions at the interface.A long life anticorrosion coating was developed based on ternary copolymer resincombined with the metal to form chemical bonding, reactive pigmentsand chelating agent. The coating showed higher anti-corrosion performance than similar imported coating, with resistance to salty water for1200h, salty spray for1000h and ultraviolet aging for2000h and having good adhesion performance under the surface treatment of level St1and St3.