RETRACTED: Construction of an excellent eco-friendly anti-corrosion system based on epoxy@Sm2O3-polydopamine biopolymer on the mild steel surface

Abstract

Abstract Metals' surface treatment by chemical conversion coatings (CCs) is one of the most promising methods for improving the organic coatings adhesion strength as well as the corrosion protection properties on the metal substances. Since most of the recently used conventional CCs, i.e., chromate/phosphate-based ones, have undesired environmental problems; nowadays, several non-hazardous chemical treatment solutions based on the rare earth metals (REM), such as Sm-CC, are applied to improve the EC/steel substrate interfacial adhesion level and corrosion resistance of the organic coatings. Despite the eco-friendly nature of the REM-based CCs, they cannot provide high corrosion resistance due to some structural problems. Therefore, finding appropriate and bio-compatible approaches for improving Sm-CC properties is the new topic of research. In the present work, a green/non-toxic surface treatment approach has been used to improve the corrosion resistance of the epoxy coating (EC) on the mild steel (MS) surface. For this objective, a green anti-corrosion composite film based on samarium CC-poly-dopamine (SmPDA) was applied on the MS surface. PDA NPs were obtained by oxidation of dopamine molecules in two different ways, i.e., self-polymerization (PDA1) and oxidant-induced polymerization (PDA2). The deposited SmPDA film morphology and chemical structures were characterized by SEM/EDS and Raman spectroscopy methods. The EC corrosion protection performance evaluation was conducted by electrochemical impedance spectroscopy (EIS) and salt-spray test. Besides, the cathodic delamination (CD) rate and adhesion strength were measured. SEM/EDS analysis and Raman spectroscopy results revealed that nanostructure samarium and graphene-like PDA films were developed on the MS surface via SmPDA chemical modification. Moreover, EIS achievements demonstrated that the Rt values of the EC and scratched EC samples applied on the surface treated MS substrates are 37600 MΩ.cm2 and 90830 Ω.cm2, respectively. These values ​​are about 1375 and 19 fold more than the Rt of those applied on the un-treated MS coupons, respectively. The qualitative salt-spray test results illustrated that via SmPDA treatment, the less disbonding and blistering have occurred on the EC. The EC applied to SmPDA2 treated MS showed better corrosion protection performance than SmPDA1. In addition, by SmPDA2 surface treatment, the CD rate of the EC decreased about 92%, and its adhesion strength increased by about 118%.