Preparation And Study Of Cerium(Ⅲ)- Modified Triazinedithiol Polymeric Nanofilm For Corrosion Protection Of Aluminum Alloy

Due to two highly reactive thiol groups and thermally stable triazine ring, triazinedithiol compounds have been used as a protective nanofilm on the surface of the metal. Besides, technological process of the triazinedithiol nanofilm is simple, innocuous and pollution-free, and the nanofilm has excellent anti-corrosion property. However, the polymeric nanofilms fabricated by traditional techniques have the propensity for containing molecule-sized defects to some extent, which results in the thickness of the nanofilm dropping, and limits its application in more fields. In order to improve the property of the polymeric nanofilm, some methods have been widely investigated during the past few years, such as the change of the substituent on triazinedithiol’s structure, the alliance of electrodeposition and self-assembled method, as well as the fabrication of complex polymeric nanofilm. As a promising environmentally coating, it has not been reported so far to dope inert or active nanoparticles into the triazinedithiol polymeric nanofilm. Therefore, it is very necessary to study the effect on inert or active nanoparticles into the triazinedithiol polymeric nanofilm.In this paper, we applied AA5052 aluminum alloy as substrate and 6-(N,N-dibutyl)amino-1,3,5-triazine-2,4-dithiol monosodium(DBN) as triazinedithiol monomer to prepare the polymeric nanofilm of DBN with the help of electrochemical workstation. Meanwhile, Ce(NO3)3 as inhibitor was adopted to prepare cerium-doped polymeric nanofilm by two-step potential electrodeposition. Firstly, we studied the effect of triazinedithiol electrodeposited nanofilm with different pretreatments(polishing treatment, mixed alkali treatment, hydrazine hydrate treatment, corona treatment) on AA5052 surface, and finalize the optimum pretreatment method. Then, we determined the optimum cerium ion concentration through comparison test, and studied the property and effect of cerium modified triazinedithiol polymeric nanofilm for corrosion protection of Aluminum alloy. The concentration of DBN was 5 mmol/L, and the potential and time were 1.6 V and 30 s for the first step and then polymerized at 6.0 V for 10 s of the second step. The samples were cured for 10 min at 100 ℃. The results were as follows:(1) The best condition of pretreatment before coating was corona treatment, and corona treatment not only did not damage the matrix surface but also enhanced the hydrophobicity and anti-corrosion ability of polymeric nanofilm on the substrate surface.(2) The optimum concentration of cerium ion was 0.5 mM. The cerium modified PDB nanofilm presented the best hydrophobicity, and the corrosion current density was the smallest and the protection efficiency was the highest when the concentration of cerium ion was 0.5 mM.(3) FT-IR analysis results showed that polymeric nanofilms were formed on AA5052 substrate surface by electropolymerization of DBN no matter whether cerium was added or not.(4) The electrochemical measurements of open circuit potential(OCP), potentiodynamic polarization(PDP) and EIS results revealed that the substrate surface covered by cerium-doped polymeric nanofilm had remarkable anti-corrosion property.(5) When the metal corrosion occurred, cerium might come out to produce the precipitation of cerium hydroxides or cerium oxides to protect the substrate in the vicinity of the cathodic sites, where hydroxide ion were formed from the oxygen reduction reaction. Therefore, incorporating cerium into triazinedithiol nanofilm was believed to enhance anti-corrosion performance.